Snakes of the World: A Guide to Every Family 9780691240671

Table of contents :
CONTENTS
Introduction
The Snake Infraorders and Superfamilies
Scolecophidia: Superfamily Typhlopoidea
Alethinophidia: Clade Amerophidia
Alethinophidia: Clade Afrophidia: Clade Henophidia
Alethinophidia: Clade Afrophidia: Clade Caenophidia
Glossary
Resources
Index
Picture Credits and Acknowledgments

Citation preview

SNAKES

OF THE WORLD

SNAKES

OF THE WORLD

A GUIDE TO E V E R Y FA M I LY Mark O’S he a

PRINCETON UNIVERSITY PRESS PRINCETON AND OXFORD

Published in 2023 by Princeton University Press 41 William Street, Princeton, New Jersey 08540 99 Banbury Road, Oxford OX2 6JX press.princeton.edu Copyright © 2023 by Quarto Publishing plc All rights reserved. No part of this publication may be reproduced or transmitted in any form, or by any means, electronic or mechanical, including photocopying, recording or by any information storage-and-retrieval system, without written permission from the copyright holder. Requests for permission to reproduce material from this work should be sent to [email protected] Library of Congress Control Number 2022942457 ISBN: 978-0-691-24066-4 Ebook ISBN: 978-0-691-24067-1 British Library Cataloging-in-Publication Data is available Printed and bound in Singapore 10 9 8 7 6 5 4 3 2 1 This book was conceived, designed, and produced by The Bright Press, an imprint of the Quarto Group The Old Brewery, 6 Blundell Street, London N7 9BH, United Kingdom www.Quarto.com Publisher James Evans Editorial Director Isheeta Mustafi Managing Editor Jacqui Sayers Art Director James Lawrence Senior Editor Joanna Bentley Project Manager Caroline Earle Design Wayne Blades Illustrations John Woodcock Picture Research Kathleen Steeden Cover Design Emily Nazer Cover photos: Front cover, clockwise from top-left: Shutterstock/Alex Stemmers; Shutterstock/Sarah2; Shutterstock/Eric Isselee; Shutterstock/ PetlinDmitry; Shutterstock/Raja Seni; Shutterstock/Eric Isselee; Mark O’Shea; Shutterstock/Eric Isselee; Shutterstock/Eric Isselee; Shutterstock/blackboard1965; Shutterstock/PetlinDmitry. Spine: Shutterstock/ Pascal Guay. Back cover: Shutterstock/Nynke van Holten.

6

Introduction

CONTENTS 66

68

84

90

128

232 234 236 240

The Snake Infraorders and Superfamilies Scolecophidia: Superfamily Typhlopoidea Alethinophidia: Clade Amerophidia Alethinophidia: Clade Afrophidia: Clade Henophidia Alethinophidia: Clade Afrophidia: Clade Caenophidia Glossary Resources Index Picture Credits and Acknowledgments

| The Reticulated Python (Malayopython reticulatus), from Southeast Asia, holds the record as the longest snake species, with lengths of up to 33 ft (10 m). below

INTRODUCTION | The Naga Buddha statue depicts Lord Buddha seated on the coils of the seven-headed cobra Mucilanda who shelters him while he meditates. It is one of the most powerful symbols in Buddhism. below

6

Introduction

Snakes, along with their close relatives the lizards and worm-lizards, comprise the Squamata, the “scaled reptiles,” the most successful and enduring successors from the Ruling Age of the Reptiles. Snakes may be very small, the smallest being the Barbados Blindsnake (Tetracheilostoma carlae), which exhibits a scientific name almost longer than it is itself (maximum 4 in/100 mm), but others may be simply huge, such as the Reticulated Python (Malayopython reticulatus), which may achieve 33 ft (10 m) in length, or the heavy-bodied and aquatic Green Anaconda (Eunectes murinus), which may weigh 220 pounds (100 kg). The largest snake that ever crawled on Earth is believed to have been Titanoboa (Titanoboa cerrejonensis), which grew to 42 ft (12.8 m) during the Late Pleistocene 60–58 million years ago (mya). Today the Earth is inhabited by over 4,000 snake species, which inhabit every continent except Antarctica, two of the great oceans, and most of the world’s tropical and temperate islands. They inhabit almost every habitat imaginable, from lush rainforest to inhospitable desert, from mountain tops to Arctic tundra, and even our own homes. They live on land,

under the ground, in the trees, and in both freshwater and saline habitats; and a few have taken advantage of a close association with humans to spread around the world. Snakes are ectothermic, commonly referred to as “cold-blooded,” although this is a misleading label since their blood need not be cold. Snake bodies and heads are entirely covered with scales, arranged in such a regular way that they are one of the primary means used to distinguish between species. Snakes lack limbs, although a few basal families retain the vestiges of the hind limbs as a pair of spurs either side of their transversely positioned cloaca (common genital-excretory opening). They lack external ear openings, possess lidless eyes that are covered with a transparent protective “brille,” so they cannot blink, and they shed their skins as they grow, frequently in a single piece. All snakes possess a chemosensory forked tongue, while some possess thermosensory facial pits, used for hunting endothermic prey. Most are completely harmless to humans, even many of the technically venomous species. Many modern snakes are “macrostomatans”­—they have large mouths capable of devouring prey broader than their own heads due to the two halves of the lower jaw being both articulatable and separated at the

chin. Unlike the lizards, there are no herbivorous snakes, they are all carnivores, but the size of their prey ranges from ants to antelopes. Most snakes are oviparous (egg-laying) but viviparity (live-bearing) has evolved numerous times within the Serpentes. Snakes are rarely seen in the numbers that some lizard species may be encountered, but aggregations of snakes do occur, such as when thousands of Red-sided Gartersnakes (Thamnophis sirtalis parietalis) emerge from their hibernation dens in Manitoba, Canada; on the famous snake islands, Ilha Queimada Grande, Brazil, or Shedao Island, China, which are home to large populations of Golden Lanceheads (Bothrops insularis) and Shedao Island Pitvipers (Gloydius shedaoensis), respectively. And, finally, snakes have found their way into the belief systems and customs of almost every human group with which they interact, though not always as portents of evil. This despite the fact that a few species of highly venomous snakes are responsible for up to 138,000 snakebite fatalities a year, and up to 400,000 survivors with permanent disabilities or amputations.

| The Green Anaconda (Eunectes murinus), of South America, is the heaviest snake species in the world, achieving up to 220 pounds (100 kg) in weight. below

7

EVOLUTION AND ORIGINS OF SNAKES The evolutionary origin of the snakes is a long and hotly contested argument. Some authorities propose that snakes evolved from a group of extinct marine reptiles known as mosasaurs, but other evidence suggests that snakes evolved from within the Anguimorpha, a lizard infraorder containing slow worms, alligator lizards, the Gila Monster, and monitor lizards. While the mosasaur argument still has support, the consensus seems to lean toward an anguimorph lizard origin. The earliest ancestral snake is probably Eophis underwoodi from Mid-Jurassic Oxfordshire, England (c.167 mya). It is only known from some fragments of jaw bone.

| A fossil of Pachyophis woodwardi from the Late Cretaceous (94–100 mya) discovered in Herzegovina. The skull is lepidosaurian, the lower jaw dolichosaurian, the teeth snake-like suggesting Pachyophis belongs in the Simoliophidae, the marine rear-legged snakes that belong in the Ophidia (pan-snakes) but not the Serpentes (crown-snakes), it belongs to an ancient extinct group of snakes. below left

THE FOSSIL RECORD

Being elongate and composed mostly of a fragile backbone, snake skeletons do not make good fossils. In death they quickly become disarticulated and scattered, so complete snake fossils are a rare find. The skulls of snakes are also extremely fragile, but one way to distinguish between a fossil snake skull and that of a fossilized lizard is to examine the teeth. Lizards exhibit a diverse array of different teeth for dealing with a range of food types, from

8

Evolution and Origins of Snakes

vegetation, to hard-shelled snails, to carrion, whereas snakes are entirely carnivorous and generally swallow their prey whole, so snakes’ teeth (excluding fangs, if present) are used to maintain a grip on the prey while it is being subdued and swallowed. Therefore, snake teeth are strongly recurved, and homogenous. We also know that the presence of hind limbs does not rule out a fossil being that of a snake because remnant hind limbs are still present in modern boas and pythons. Certainly there were snakes in the Late Cretaceous that possessed hind limbs, for example, Eupodophis descouensi, a marine snake with short hind limbs from Lebanon, and Najash rionegrina from Patagonia, which had longer, more well-developed

| The earliest snakes probably resembled the small-mouthed Asian pipesnakes (Cylindrophis spp.) of today which feed on narrow, cylindrical prey. below

(Cylindrophis spp.), and that they inhabited lushly vegetated, humid habitats. The real surge in serpentine evolution occurred much later, probably as a result of the Cretaceous-Paleogene (K–Pg) Extinction Event, 66 mya, which brought about the extinction of the dinosaurs, and heralded the rise of both snakes and mammals. THE LARGEST SNAKE THAT EVER CRAWLED

| This replica of Titanoboa (Titanoboa cerrejonensis), in the Smithsonian Institution, is shown swallowing a small crocodilian, something that several species of modern snakes have also achieved. Alongside the humans, the true size of this snake can be fully appreciated. below right

Such an explosion in small mammal diversity would likely have provided the ideal opportunity for a similar expansion in snake diversity and, with plenty of prey and ecological niches available, snakes will have diversified greatly. Only 10 million years after the K–Pg Event, a snake became a climax predator. Titanoboa cerrejonensis, from Colombia, is the longest snake known to have ever existed; it achieved a length of 42 ft (12.8 m) and an estimated weight of around 1,135 kg—more than twice the weight of a one-year-old baby elephant. The diversification of snakes continued apace over the following 60 million years so that today we share the planet with at least 4,000 snake species.

hind limbs. However, the much-lauded Brazilian “four-legged snake” Tetrapodophis amplectus, reported in 2016, is now believed to be a dolichosaur, an extinct marine lizard. EARLY SNAKES

The earliest positively identified fossil snakes, comprising a few vertebrae and jaw bones containing homogenous recurved teeth, were discovered in England, Portugal, and Colorado, USA and dated to the Mid-Jurassic or Early Cretaceous (167–140 mya). It is likely that the very earliest snakes were small, terrestrial, nocturnal predators of soft-bodied invertebrates or elongate vertebrates, not dissimilar to modern pipesnakes 9

TAXONOMY OF SNAKES Humans, with their tidy minds, like to be able to categorize things, to put them in boxes with labels on the outside. We have probably always done this: early humans painting on the walls of their caves may have separated animals into those that were good to eat, those that were not good to eat, and those that were likely to eat them. Understanding is power, but the trouble is that nature is not easily pigeon-holed; evolution is a fluid and ongoing process that is taking place even as these words are being written. Not every organism is at the same stage in its evolutionary journey, and even what constitutes a species, the basic building block of taxonomy, depends on the type of organism concerned and the thinking of the researcher. There are more than 26 species concepts. A NOTE ON TAXONOMY AND SCIENTIFIC NAMES

The science of classifying nature is called “taxonomy”; it is the process by which we try to place organisms into named boxes at different hierarchical levels; for example, we call all living organisms with feathers “birds” and place them in the class Aves. We call these boxes clades—groups that contain an ancestor and all its descendants— because today taxonomy seeks to mirror evolution and groups related organisms together. These clades may have official hierarchical ranks, or they may not. Those that do are listed as (largest to smallest): domain, kingdom, phylum, class, order, family, genus, and species, with a series of nested intermediate levels that may include infraorder (below order but above

10

Taxonomy of Snakes

family), superfamily (above family but below infraorder), subfamily (below family but above genus) or subspecies (below species). Examples of snake clades that do not have official ranks are Afrophidia and Amerophidia. As will be seen, they lie somewhere between the infraorder Alethinophidia and its superfamily levels. To help us in our quest to organize and classify organisms we give each one a unique name, and this is where nomenclature, the taxonomic book-keeping tool, comes into play. We allocate every living creature a binomial name made up of a generic first part and a specific second part, for example, Homo sapiens for humans. We then place H. sapiens into the genus Homo with other closely related (but now extinct) species of upright walking apes, such as H. erectus or H. neanderthalensis, and by doing so we are stating that we consider these three species more closely related to each other than they are to the gorillas (genus Gorilla) or the chimpanzees (genus Pan). All three related genera are placed in the subfamily Homininae, as distinct from the orangutans (genus Pongo) in the subfamily Ponginae, but both Homininae and Ponginae are placed in the family Hominidae. There are clues to the ranks of certain clades; for example, the suffixes -oidea indicate a superfamily; -idae, a family; and -inae, a subfamily, respectively, as in Colubroidea, Colubridae, and Colubrinae. All of the names above the level of genus are proper nouns and written with a capital initial letter, for example, “Elapidae is a family of highly venomous snakes” unless they are being used as common nouns, in which case a lowercase initial is used, “elapids are highly venomous.”

PHYLOGENY OF SNAKES

ANOMALEPIDIDAE LEPTOTYPHLOPIDAE (2 subfamilies)

SCOLECOPHIDIA

TYPHLOPOIDEA

GERRHOPILIDAE XENOTYPHLOPIDAE

TYPHLOPIDAE (4 subfamilies)

PYTHONOIDEA

BOOIDEA

UROPELTOIDEA

HENOPHIDIA

AFROPHIDIA

AMEROPHIDIA

ANILIOIDEA

CAENOPHIDIA

illustrating the divergences between the infraorders Scolecophidia and Alethinophidia, also the alethinophidian clades Amerophidia, Afrophidia, Henophidia, and Caenophidia, and the superfamilies (suffix -oidea) Typhlopoidea, Anilioidea, Uropeltoidea, Pythonoidea, Booidea, Acrochordoidea, Xenodermoidea, Pareoidea, Viperoidea, Homalopsoidea, Elapoidea, and Colubroidea. The Serpentes contains 42 families (suffix -idae), 8 of which contain 2–4 subfamilies (which are not listed here but would have the suffix -inae). This is a simplified family tree, the lengths of the arms are not intended to indicate the timelines since divergence between the various infraorders, families, and subfamilies. Extinct taxa and lineages are omitted. The elapoid incertae sedis genera Buhoma and Micrelaps are also omitted. This tree is based on several published phylogenetic trees including Zheng & Weins (2016) Molecular Phylogenetics and Evolution 94:542; Zaher et al. (2019) PLOS One, and Burbrink et al. (2020) Systematic Biology.

SERPENTES

| A family tree of the snakes

ALETHINOPHIDIA

right

ACROCHORDOIDEA XENODERMOIDEA PAREOIDEA VIPEROIDEA HOMALOPSOIDEA

ELAPOIDEA

ANILIIDAE TROPIDOPHIIDAE XENOPHIDIIDAE BOLYERIIDAE ANOMOCHILIDAE CYLINDROPHIIDAE UROPELTIDAE XENOPELTIDAE LOXOCEMIDAE PYTHONIDAE BOIDAE ERYCIDAE CANDOIIDAE CHARINIDAE UNGALIOPHIIDAE CALABARIIDAE SANZINIIDAE ACROCHORDIDAE XENODERMIDAE PAREIDAE (2 subfamilies)

VIPERIDAE (3 subfamilies) HOMALOPSIDAE CYCLOCORIDAE PSEUDASPIDIDAE ELAPIDAE (2 subfamilies) PROSYMNIDAE PSAMMOPHIIDAE LAMPROPHIIDAE PSEUDOXYRHOPHIIDAE ATRACTASPIDIDAE (2 subfamilies) SIBYNOPHIIDAE CALAMARIIDAE GRAYIIDAE COLUBRIDAE (2 subfamilies)

COLUBROIDEA

NATRICIDAE PSEUDOXENODONTIDAE DIPSADIDAE (3 subfamilies)

Only the binomial (genus and species) or trinomial (genus, species, and subspecies) names are italicized, and only the genus has a capital initial, for example, subspecies Thamnophis sirtalis parietalis, even when named for a person or place, such as the species Crotalus ericsmithii or Leptophis mexicanus.

11

DEFINING SNAKES

Readers may come across two names being used scientifically for snakes as a whole, Serpentes and Ophidia, but they are not interchangeable. Three other terms are useful to know in order to understand the differences. “Basal” means the earliest, most primitive, forms, likely to be extinct; “crown” means the most recent and advanced forms, more likely to be extant; and “pan” is all encompassing and includes the basal and crown taxa and all those in between. The Serpentes is the clade containing all modern snakes so it may be considered a crown taxon, while Ophidia is a clade containing not only the Serpentes but also all extinct snakes back to their earliest origins with Eophis, Eupodophis, and Najash, so it is a pan taxon. This volume is primarily concerned with the Serpentes, the suborder of the order Squamata that contains the modern snakes. It has been stated that the snakes arose from within the Anguimorpha, one of six infraorders of lizards, which contains slow worms, the Gila Monster, and monitor lizards. If we were seeking a single sentence definition of a snake 12

Taxonomy of Snakes

| A Northern Alligator Lizard (Elgaria coerulea) demonstrating body elongation and limb reduction, part of the trend toward limblessness in the Anguiomorpha which led to snakes. left

| Often mistaken for a snake, the Scheltopusik (Pseudopus apodus) from southeastern Europe, is a near legless lizard, though it retains scaly flaps as hind limbs. above

| The Eastern Cape Lance Skink (Acontias meleagris) is a member of the lizard family Scincidae in which the trend toward limblessness and body elongation is represented in several unrelated genera. right

| The European Slow Worm (Anguis fragilis) is the ultimate legless lizard; it does not even have vestigial hind limbs so it is more legless than a python or boa, which do. below

we might write: “An elongate, ectothermic, limbless reptile, covered in keratinized scales, which sheds its entire external outer layer at irregular intervals, lacks movable eyelids or external ear openings, but possesses a forked chemosensory tongue and a three-chambered heart, with males possessing paired hemipenes, and females laying eggs or giving birth to live neonates usually once a year, and possessing

articulatable lower jaws, with which it feeds on a range of other animals that are swallowed whole.” Of course, not everything that is limbless, or seemingly limbless, is a snake. The trend toward limblessness, combined with body elongation, the loss of eyelids and external ear openings, is a common theme that has occurred numerous times independently in squamate reptiles. The amphisbaenians, the Slow Worm (Anguis fragilis), the Scheltopusik (Pseudopus apodus), and the lance skinks (Acontias spp.) being just a few examples. There are at least 4,000 extant species of snakes, which are placed in 538 genera, in 42 families, 12 superfamilies, and two infraorders. New snake species are described with some regularity: 43 in 2018, 52 in 2019, 68 in 2020, and 67 currently valid species in 2021. There were fewer than 3,200 species when this author purchased his first book on snakes in the 1960s and in the last half of the twentieth century an average of 12 species, which are still considered valid, were described each year, so it can be seen that the rate of discovery has accelerated in recent years. 13

INTERNAL ANATOMY Despite its superficial resemblance to an earthworm, even the tiny, shiny Brahminy Blindsnake (Indotyphlops braminus) is an advanced vertebrate organism with a miniaturized serpentine skeleton and internal organs. The lack of limbs in a snake might be seen as primitive, looking at it from a biased human viewpoint, but leglessness is actually an advanced characteristic in squamate reptiles, with numerous lineages of lizards demonstrating everything from the typical pentadactyl tetrapod (five-toed, four-legged) lizard to highly derived legless skinks, pygopodid lizards, and slow worms. Snakes are just another highly derived group of legless lizards. | A rattlesnake skeleton (Crotalus spp.) demonstrating the numerous vertebrae and ribs and the highly flexible skull. The rattle is not bone but skin, one link left behind after every skin-sloughing.

SNAKE SKELETONS

The snake skeleton is about as basic as a highly advanced vertebrate skeleton can get. It comprises a skull, composed of highly flexible bones; a pair of articulatable lower jaws that are not fused at the chin (as they are in lizards and mammals); a long vertebral column, which may contain up to 450 individual vertebrae, with a pair of ribs attached to each; and up to 250 additional ribless vertebrae in the tail. There is no sternum (breastbone), no pectoral girdle (shoulders) or forelimbs, and, except for the more basal boas and pythons, no pelvic girdle or hind limbs. In the boas and pythons, and related

below

14

Internal Anatomy

| The small shiny Brahminy Blindsnake (Indotyphlops braminus) aka Flowerpot Snake, is easily mistaken for a worm, but it is a genuine snake. left

TYPICAL SNAKE

henophidian (“old snake”) families, the remnants of the hind limbs are reduced to a pair of spurs or claws located on each side of the cloaca, attached to the vertebral column by muscles, and vestigial pelvic bones. The lack of a sternum to hold the ribs relatively rigid on the ventral side of a snake means that the ribs and the powerful intercostal muscles that connect them can move relative to one another, forward and backward when crawling or constricting prey, or laterally when a snake is presenting an enlarged surface area while basking, when parachuting or gliding (Chrysopelea spp.), or spreading a hood (Naja spp.). The expandable rib cage also enables a snake to swallow a large meal or carry a large number of embryos or eggs. SNAKE SKULLS

A recent herpetological textbook differentiated between lizard and snake skulls, stating that “the skulls of lizards crush prey, whereas the skulls of snakes engulf prey,” (Pough et al., 2016) and that sums up the situation rather well. Snakes have sacrificed bite force for flexibility so that they can swallow their prey intact. The anterior bones of a snake’s skull are only loosely connected, and are capable of considerable

TYPICAL LIZARD

| The lizard skull is often a rigid box with a lower jaw not dissimilar to that of a mammal, fused at the chin, and containing specialized teeth to deal with a wide range of prey. A snake’s skull is more flexible and the lower jaw is not fused at the chin and is capable of considerable movement in all planes. The teeth are homogeneous, simple recurved hooks to maintain contact with the prey and direct it down the throat. above

motion, and the four tooth-bearing bones of the upper jaws, the outer maxillae and the inner pterygoids (part of the roof of the mouth in mammals), can also be moved forward or backward independently. The lower jaws are even more manipulatable because the quadrate bone, to which the mandibles are attached, is only loosely connected to the supratemporal bone of the skull and, combined with the fact that the tooth-bearing dentary bones of the mandible are not fused at the chin, this means the lower jaws are capable of a massive amount of motion in all planes, permitting a snake to work its mouth around prey much wider than its own head. Snakes have sacrificed a powerful bite for the ability to swallow large prey whole. 15

SNAKE DENTITION AND FANGS

The teeth of snakes are fairly homogeneous: simple recurved hooks to prevent prey escaping. They may be lost and replaced with some regularity, and some defensive bites from nonvenomous snakes result in teeth being left in the skin of the recipient. There are, however, some specializations in snake dentition. Kukri snakes (Oligodon spp.) are renowned for their ability to deliver defensive bites to handlers that are deep and continue to bleed for some time. This is due to their posterior-most maxillary teeth being enlarged, sharp, and laterally compressed like blades, for maintaining a grip on struggling smooth-scaled skinks or slicing into reptile eggs. Asian wolfsnakes (Lycodon spp.) possess almost canine-like enlarged anterior maxillary teeth, presumably also for holding their scincid prey.

Many other snakes possess large teeth, such as hognose snakes (Heterodon spp.), which use them to deflate toads that inflate themselves as a defense. These are all variations on the theme of a simple, sharp, recurved tooth and it is easy to see how they may become grooved to act as a conduit for venom to enter and subdue the prey during a chewing bite, beginning the transition into fangs. There are numerous rear-fanged venomous snakes that prey on invertebrates or small vertebrates that will cause nothing worse than a slightly swollen finger if they bite a human, but there are a handful capable of causing much more serious bites, even fatalities (see p.7). When a snake possesses only regular, recurved teeth it is said to be aglyphous (without knives), and when it possesses enlarged posterior-maxillary fangs it is referred to as

FANG TYPES

Aglyphous

| Snakes with solid aglyphous teeth include boas, pythons, and more advanced nonvenomous species like cornsnakes. The rear-fanged snakes are opisthoglyphous, they have a pair of enlarged, grooved fang-like teeth in the rear of the upper jaws. Proteroglyphous elapid snakes possess an enlarged, fixed fang on short maxillae. Solenoglyphous vipers possess long, hinged, hollow fangs on the maxillary bone that fold parallel with the jaw when not in use. Apart from their fangs all other teeth in the three venomous groups are aglyphous.

Opisthoglyphous

right

16

Internal Anatomy

Proteroglyphous

Solenoglyphous

| The fangs of this Variable Bushviper (Atheris squamigera) are long, hinged, and contained in a sleeve of skin called a fang-sheath. right

| The fangs of this Red Spitting Cobra (Naja pallida) are shorter than viper fangs, so they are not hinged but rather fixed in position on short, flexible maxillary bones. below

opisthoglyphous (rear-knived). There are two other conditions, proteroglyphous (front-knived) and solenoglyphous (pipe-knived). The proteroglyphous snakes are the elapids: cobras, mambas, coralsnakes, taipans, and their relatives. They possess relatively large fangs on the anterior end of an extremely short and otherwise toothless, but highly mobile, upper jaw bone (maxilla). Each fang has an almost closed channel down the center to carry venom to the orifice near its tip. The solenoglyphs are the vipers. They possess extremely long hollow-centered (pipe-like) fangs on their toothless maxillae. The fangs are so

long that the viper cannot close its mouth with them erect, so the fangs are hinged and swing backward parallel with the upper jaws when not in use. As with their teeth, it is common for venomous snakes like cobras or vipers to shed fangs during striking or feeding, and these will pass down with the meal and leave the body in the feces. With snakes that defecate infrequently, such as gaboon vipers, it is not unusual to find several fangs in the feces. The burrowing asps or stiletto snakes (Atractaspididae, pp.186–187) possess horizontal fangs with which they can stab their prey without opening their mouths when hunting in burrows. 17

INTERNAL ORGANS

As might be expected, the internal anatomy of a snake is rather similar to that of a lizard, except that everything has to fit into a more elongate body. As with lizards the heart is three-chambered, with a partially divided ventricle. There are two lungs but one, usually the right, runs for a third of the length of the snake’s body, whereas the other is small and vestigial. The kidneys, testes, and ovaries are also arranged asymmetrically. Snakes are famous for their prodigiously large meals so it will be no surprise that the stomach may take up a large proportion of the internal anatomy. However, this is not always the case. When a python is carrying a large number of 18

Internal Anatomy

eggs it will not be feeding and the stomach can shrink down to the size of an orange. After the eggs are laid and the python goes hunting again it can kill and devour a large meal, its stomach expanding rapidly to accommodate the sudden change of circumstances. Such a meal after a long period of fasting would surely kill a mammal, but then such snakes are feast and famine animals. | An Eyelash Palm-pitviper (Bothriechis schlegelii) rests after eating a very large meal. Such a meal could never have been consumed whole were it not for the articulable lower jaws and the lack of a sternum holding the ribs rigidly in place, both serpentine adaptations for prey wider than their own heads and bodies. above

INTERNAL ANATOMY OF A SNAKE

MALE Inverted hemipenes Trachea

Ventral scales Sperm duct

Heart (three-chambered) Left lung (vestigial)

Esophagus

Right lung Liver

Testes

Kidneys

Stomach Small intestine FEMALE

Pancreas Gall bladder

Spleen

Subcaudal scales Cloacal plate Ventral scales

| Snakes have the same internal organs as other vertebrates, but these are arranged asymmetrically, due to their elongated bodies. There are two lungs (the right is usually functional; the left usually vestigial) two elongate kidneys, a liver, a pancreas, a gall bladder, and a three-chambered heart. An esophagus, stomach, and small and large intestines make up the digestive system. The female sexual organs consist of a pair of elongate ovaries, while males have a pair of testes and a paired hemipenis, which is inverted inside the base of the tail until required. above & right

Ovaries

19

SNAKE SKIN AND SCALES Both snakes and lizards belong to the Squamata, the scaled reptiles. Their bodies are covered in protective keratinized scales, similar to the material fingernails are made of. Snakes are, of course, not slimy! Scales serve many purposes, such as protection from desiccation, defensive armor against attack, and rain-harvesting. In snakes, the arrangement and number of the scales on the head and body provide important clues as to the identification of its species. The large regular head scales, with specific names such as “parietals,” “preoculars,” “postoculars,” and “internasals” are often referred to as “scutes,” and some of these are super important. Highly venomous elapids (cobras and their relatives) are in many respects similar in body morphology to many harmless colubrid snakes, but elapids lack a “loreal” scale whereas most colubrids possess one. The scales on a snake’s body are usually imbricate, attached to the skin at their anterior end, but free at the posterior end where they overlap the scale behind; some seasnakes and the xenodermids (strange-scaled snakes) have juxtaposed scales that are fused to the skin all the way around and do not overlap other scales. Body scales are of four different kinds. Dorsals are regularly arranged rows of scales that cover the flanks and dorsum of the body and tail. The number of rows is usually, but not always (neotropical genera Spilotes and Chironius), an

| The large regular scales on the heads of some snakes (colubrids, elapids etc.) are called scutes and they have particular names. The number and order of these scutes provide important clues for snake identification. right

20

Snake Skin and Scales

odd number, which means there is a vertebral row down the center of the back. Dorsals may be smooth or keeled (ridged) in appearance and texture, the latter being the norm in keelbacks (Natricidae) and vipers (Viperidae). They may be arranged in transverse rows that cross the body at a right-angle to the spine, or they may be arranged obliquely, a backward-pointing diagonal to the spine. This last arrangement is common in highly arboreal treesnakes, which may also exhibit an enlarged vertebral row, the scales down the middle of the back being larger than those to either side to provide support when bridging gaps. SCALATION



Rostral Internasal Prefontal Nasal Loreal Preoculars Supraocular Frontal Postoculars Subocular Anterior temporal Temporolabial Posterior temporal Parietal Supralabial Mental Infralabial

| The dorsal and ventral scales of snakes are involved in purposes such as locomotion, climbing, rain harvesting, and may even be sensory. below

Smooth transverse dorsal scales

Smooth oblique dorsal scales

Keeled dorsal scales

Tuberculate dorsal scales

Ventral scales run the length of the underside of the snake’s body. They are usually broad and smooth, and each overlaps the one behind. Ratsnakes (Pantherophis spp.) and bronzebacks (Dendrelaphis spp.) also exhibit a longitudinal keel down either side of the ventrals, which enables them to gain a purchase on tree bark. These scales are essential for movement on land, but in extreme burrowers, such as blindsnakes and threadsnakes (Scolecophidia) or true seasnakes, they are much reduced in size. In the Pelagic Seasnake (Hydrophis platurus), the loss of the ventral scales enables it to flatten its body like a ribbon for swimming but makes it completely helpless if cast up onto a beach during a storm. After the ventrals comes the cloacal plate, a

Ventral scales

single or paired scale that covers the common genital-excretory opening, and then the subcaudals, which are usually a pair of scales on the underside of the tail. The outer epidermis of a squamate’s skin is dead, so for the snake to grow it must be shed, a process known as sloughing or ecdysis. Feeding, pregnancy, or injury can initiate or accellerate sloughing. Because they have limbs, lizards shed their skins piecemeal, but snakes normally shed the entire skin in one go, including the transparent brilles that protect the eyes and the skin from the forked tongue. The pigmented layers are deeper in the dermis so the shed skin bears only the faintest trace of the snake’s pattern. 21

SENSE ORGANS While the majority of lizards might be visually orientated, when it comes to hunting, defense, and courtship snakes are more chemosensory creatures. Most snakes possess eyes— it is a myth that they are poorly sighted—and, although they lack external ears, they are not technically deaf; but it is the forked tongue that is the primary sense organ for all snakes, and the boas, pythons, and pitvipers have also evolved a thermosensory method of prey location. TONGUES AND NASAL AND VOMERONASAL ORGANS

Every snake in the world possesses a forked tongue. If what you are holding is long, legless, and covered in dry scales, but it does not have a forked tongue, it is not a snake; it is a legless lizard. Forked tongues are not unique to snakes, however; they are also found in the monitor lizards (Varanidae), which use them for the same purpose: finding a meal or a mate. A snake’s forked tongue is located in a sheath in the front of the mouth, just anterior to the “glottis,” an extendable,

| A gartersnake (Thamnophis spp.) flicking its tongue, which forms the usual Y-shape. above

| The vinesnakes (Ahaetulla spp.) often keep the tines of their tongues parallel, like a tuning fork, and almost motionless when hunting, possibly so that its presence is not given away by the movements of a flickering, brightly colored forked tongue. left

22

Sense Organs

| When rattlesnakes (Crotalus spp.) flick their tongues they often include a moment where the tongue is briefly held above the head before continuing the tongue-flicking sequence. right

closeable airway in the floor of the mouth that enables snakes to open their mouths underwater without drowning, or take 20 minutes to swallow a large prey item without choking. When a snake protrudes its tongue, it passes through a small opening in the front of the mouth called the “lingual fossa”; it does not need to open its mouth to tongue-flick. Tongue-flick intensity increases when snakes are trailing a prey animal, envenomed prey, or a mate, and also when they feel threatened and need rapid information retrieval. Every time the tongue flicks out it collects scent molecules on its wet surface, and when it returns to the mouth it transfers these to a tubular organ in the roof of the mouth called Jacobson’s organ. Jacobson’s organ is a vomeronasal or olfactory organ located in the mouth of many reptiles (not crocodilians) and mammals, including humans where it is vestigial, but it is most developed in squamate reptiles, especially snakes, where it comprises a pair of tubules lined with sensory tissues. The returning tongue deposits scent molecules on the anterior lingual processes in the floor of the mouth and from here they are transferred to the Jacobson’s organ, contrary to

common belief the tongue does not actually contact the organ. An analysis of the molecules is then carried to the snake’s brain via the olfactory nerve, and the snake alters its behavior accordingly. It seems logical, with a pair of forks, that the collection of more molecules on one or other tine may provide directional information also, but this is yet to be confirmed. The nostrils of snakes are also full of sensory tissues for the collection of scent molecules— these are highly chemosensory creatures. One interesting aspect of tongue-flicking concerns the posture of the tongue. Most snakes form a perfect V-shape with their tongues, but the highly cryptic vinesnakes (Ahaetulla spp.) often keep the fork tines parallel, like a tuning-fork, with occasional withdrawals of the tongue as they approach prey, possibly as part of their behavioral camouflage. Some aquatic snakes, like filesnakes (Acrochordus spp.), form more of a T-shape, which may enable them to collect information over a wider area, whereas rattlesnakes (Crotalus spp.) often curl their tongues upward and over their heads, then downward again, making several slow-motion flickers before withdrawing the tongue into the mouth. 23

VISION AND EYES

The fossorial blindsnakes (Typhlopidae) are not actually blind; most possess rudimentary eyes with photosensitive cells underneath their translucent head scales. It is doubtful that they can see shape or movement, being used to a subterranean existence, but these eyes may warn the snake it has been uncovered, and cause it to quickly burrow to safety. The most obvious difference between the eyes of different snakes is the shape of the pupil, with those of primarily diurnal snakes being round, while those of nocturnal snakes are vertically elliptical, or “cat-eyed.” This is to enable the snake to control how much light reaches the extra-sensitive retina of a nocturnal snake. Of course, snakes never blink; they lack movable eyelids but instead possess a transparent, protective brille over the eye, which is shed with the skin— think contact lenses. Most snakes have their eyes 24

Sense Organs

| The vertically elliptical catlike pupil of a Green Bushviper (Atheris chlorechis) suggests a nocturnal lifestyle. left

| A round pupil, as in this Emerald Ratsnake (Gonyosoma prasinus), usually indicates diurnal activity. above

| The horizontal pupil of Günther’s Vinesnake (Ahaetulla dispar) is believed to provide the vinesnake with greater visual acuity and enable it to locate and stalk alert camouflaged lizards. right

| The eyes of the Namib Viper (Bitis peringueyi) are arranged dorsally so the snake can burrow down in the sand and still watch for prey or predators. far right

positioned on the sides of the head, with an overlap in the vision from each eye in front of the snout. Some sand-burrowing species like the Namib Viper (Bitis peringueyi) or Arabian Sandboa (Eryx jayakari), have their eyes positioned more dorsally so that they can keep the head hidden but still observe for prey or predators. Some freshwater species, for example, adult anacondas (Eunectes spp.), also have more dorsally positioned eyes. A vertebrate eye contains a retina comprising two main types of visual cells: rods for night vision, and cones for visual acuity and color vision. It was once thought that snakes had poor vision and could not see in color, but both suppositions are untrue. Snakes are very alert to movement, though less aware of shapes. A cobra is exceedingly alert to movement, which is how a snake charmer is able to hold its attention with slight body movements or moving the tip of the pipe (the cobras cannot hear the music, of

course). If the charmer stops moving, they are, from the cobra’s point of view, no longer there, so the snake will drop its hood and begin to move away, but will rapidly turn back and hood again should the charmer move the pipe. It is also untrue that snakes cannot see color. It is likely that some diurnal snakes have dichromatic or even trichromatic vision, like humans. The snakes with probably the greatest visual acuity are the Asian vinesnakes (Ahaetulla spp.). These diurnal snakes hunt camouflaged lizards in the vegetation and they rely a great deal on vision. The vinesnake’s retina has a highly sensitive cone-heavy region called the “fovea centralis,” and with its horizontal pupils and grooves down its elongated snout it will see the slightest movement of its lizard prey; like a sniper with a rifle, and with a 45-degree frontal overlap in vision from each eye, it can even judge the distance to its target. 25

HEARING AND EARS

Snakes lack external ear openings and a tympanum (ear drum), and the tiny bones associated with the ears in other terrestrial vertebrates are attached to the columella bone, itself attached to the quadrate bone at the rear of the upper jaw. Although snakes may not hear airborne sound, they can detect the vibrations of approaching footsteps—so walk softly when looking for snakes. HEAT SENSITIVE PITS

Snakes are ectothermic (cold-blooded) reptiles that often feed on endothermic (warm-blooded) prey, and three groups have independently evolved specialized thermosensory organs for the location of such prey. These organs are generally known as “pits” and they are the basis for the collective noun “pitvipers” for members of the subfamily Crotalinae, which inhabit the Americas and much of Asia. The “loreal pit” is clearly visible on the side of a pitviper’s head, between the eye and the “naris” (nostril) but slightly below a direct line between the two, in the part of the head known as the loreal region. If the pitviper is viewed from the front, the laterally facing nares are not visible, but the loreal pits are very conspicuously forward-facing. The organ comprises a hollow pit with a narrowed opening and a membrane, rich in thermosensory cells, stretched across the rear, behind which there is an air-filled space for insulation. The pit detects any infrared body warmth emanating from potential avian or mammalian prey. The pit lips create shadows on the membrane and using data entering the pits on either side of the head, pitvipers are able to triangulate and determine both direction and distance to target. It has also been determined that water evaporation from the nasal passages of the pitviper lowers the 26

Sense Organs

temperature of its head below that of its body, further enhancing its ability to detect the temperature of the prey; the pitviper’s brain effectively receives an infrared image of its prey’s position. Pitvipers are not the only snakes to use their prey’s warm body temperature as a means of locating a meal. Both boas (Boidae) and pythons (Pythonidae) independently evolved heat-sensitive pits, but in these snakes the pits are “labial,” found in a row along the upper and lower lip-scales, and in the rostral scale on the snout. It is interesting to note that in pythons that feed primarily on ectothermic prey, such as the lizard- and snake-eating Black-headed Python (Aspidites melanocephalus), thermosensory pits are absent. OTHER SENSE ORGANS

Under extreme magnification the curious tuberculate scales of the aquatic filesnakes (Acrochordus spp., p. 21) can be seen to possess tiny hairs, which may be part of a sensory system to detect fish swimming close by in turbid waters. The two tentacles of the Tentacled Snake (Erpeton tentaculatum) are also mechanosensory organs that detect the movements of fish swimming close to the head at night or in turbid water. In clear water these snakes rely more on vision to locate their prey.

| The loreal pits of a Gumprecht’s Green Pitviper (Trimeresurus gumprechti) face directly forward, the nostrils face to the side. above

| Boas and pythons, such as this Rough-scaled Python (Morelia carinata), possess rows of pits along their upper and lower labials (lip-scales). right

| The strange Tentacled Snake (Erpeton tentaculatum) is a freshwater snake with a pair of fleshy tentacles on its snout that detect the movements of fish in the water, rather like the whiskers of sealions. far right

27

LIFE IN EXTREME CONDITIONS Snakes are an extremely successful vertebrate group that have colonized much of the world, including islands far from other land, albeit sometimes through anthropogenic means. But they are still ectothermic, air-breathing, freshwaterdrinking reptiles, and there are parts of the planet where the environmental conditions would appear incompatible with reptilian existence. COLD ENVIRONMENTS

For a reptile that relies on being able to warm its body by basking in the sun in order for its metabolism to function, the colder regions of the planet are probably the most inhospitable, and indeed there are many places where endothermic mammals can exist but reptiles are absent. But there are reptiles living close to the edge in some fairly cold regions and some of those are snakes. The northernmost snake in the world is the Northern Adder (Vipera berus), which occurs over 125 miles (200 km) north of the Arctic Circle in Scandinavia and Siberia. In North America,

28

Life in Extreme Conditions

gartersnakes (Thamnophis spp.) and rattlesnakes (Crotalus spp.) are also found in the higher latitudes, though not as high as the Northern Adder. The southernmost snake in the world is the Patagonian Lancehead (Bothrops ammodytoides) which, as its name suggests, occurs deep into southern Argentina. All these species, and the three snakes inhabiting Australia’s southern island of Tasmania, the Tigersnake (Notechis scutatus), Australian Copperhead (Austrelaps superbus), and White-lipped Snake (Drysdalia coronoides), have a trick up their metaphorical sleeves: they are viviparous (live-bearers) and can exist where the eggs of oviparous species would perish (see Reproduction pp.42–43). Similarly, it is cold at high elevations, but while the Himalayan Pitviper (Gloydius himalayanus), which occurs up to 16,000 ft (4,900 m), is also viviparous, curiously the Xizang Hot-spring Snake (Thermophis baileyi), which occurs at similar elevations in Tibet (Xizang), is thought to be oviparous—possibly the clue to its ability to survive is in its common name.

| The Arabian Sand Viper (Cerastes gasperetti) is active at night, avoiding the heat of the day. above

| An angry Puff Adder (Bitis arietans) draws itself into a strike position and issues a long, loud warning hiss, but that hiss is expensive for the snake because it expels valuable moisture. right

| The Northern Adder (Vipera berus) is the northernmost snake species in the world, occurring 125 miles (200 km) north of the Arctic Circle in Scandinavia. far left

| The Xizang Hot-spring Snake (Thermophis baileyi) occurs high in the Himalayas but is believed to be oviparous. below left

HOT AND ARID ENVIRONMENTS

Snakes would seem the ideal inhabitants of hot, arid deserts, but they can die more quickly from overheating than from the cold, so even snakes have to adapt to such locations. The obvious adaptation is to become nocturnal during the hottest part of the year. Another would be shuffling down into the sand as, for example, do the sand vipers (Cerastes spp.). Avoiding being cooked alive is only half of the problem, conservation of valuable water is another. Desert snakes often have keeled scales, which collect early morning dew or sea mist in coastal sand

dune locations. The snakes can then drink the water off their own bodies. They also want to avoid losing body moisture. Every time a snake hisses it is expelling air, and that air contains moisture, so the loud and forceful hiss of a Puff Adder (Bitis arietans) might be quite costly if continued for long periods. Another form of audible warning, which does not involve breathing out repeatedly, might be required; the rattling of a rattlesnake (Crotalus spp.) or the saw-scaling of a carpet viper (Echis spp.) convey the same message as a loud hiss but do not expend valuable moisture. 29

SALINE ENVIRONMENTS

The snakes that live in the most saline environment are the true seasnakes, such as the Pelagic Seasnake (Hydrophis platurus), which may spend their whole lives out of sight of land. Even far from land they can obtain a drink when rainwater pools on the surface of the salty ocean for a while before mixing. Seasnakes will surface to take advantage of this occasional resource. Their skin is less permeable to water than the skin of terrestrial snakes, so they lose far less water to osmosis through the skin to the ocean. But there is no escaping the fact that seasnakes live on an extremely saline diet, marine fish, and salt will build up in their bodies and could reach potentially lethal levels. The way the Pelagic Seasnake deals with this problem is via a salt-excretory gland under its forked tongue; every time the tongue flicks out it carries crystalline salt out with it. 30

Life in Extreme Conditions

The truly marine seasnakes are viviparous and able to give birth at sea and although species like the Persian Gulf Seasnake (Hydrophis lapemoides) need to give birth in shallow water they do not need to come onto land, as must the more primitive oviparous sea kraits (Laticauda spp.). Another amazing adaptation of marine snakes is their ability to dive to depths of 330 ft (100 m), remain submerged for up to two hours, and then surface again without suffering from “the bends,” which occurs when nitrogen forced into solution in the blood at the high pressures of depth is released and forms potentially fatal air bubbles in the blood. The adaptations seasnakes have evolved to cope with safe, deep diving are several, complex, and beyond the space available here so the reader is referred to “Life in the Sea” (O’Shea 2005, Venomous Snakes of the World, p. 23).

| The Pelagic Seasnake (Hydrophis platurus) is the ultimate marine snake. It has salt excretory glands under its tongue, valvular nostrils to prevent the entry of seawater, drinks rainwater, and gives birth in the ocean far from land. left

| The Olive Seasnake (Aipysurus laevis) can flatten its entire body to match its paddle-shaped tail for effortless swimming. right

| The Chinese Sea Krait (Laticauda semifasciata) is a graceful swimmer but being oviparous it cannot stray too far from land. below

LOCOMOTION Snakes may lack limbs but that does not mean they have not evolved a diverse array of forms of locomotion to deal with different substrates and different lifestyles. Probably the most important factor in snake locomotion is the lack of a sternum (breastbone), which means the ribs, and the intercostal muscles between them, have a great degree of mobility and flexibility. CRAWLING

The most common form of locomotion used by snakes is serpentine or lateral undulation, whereby the body is formed into a series of S-shaped curves as the snake moves forward. This form of locomotion can be used on many surfaces, including in the water, and it may be slow and languid or rapid. The snake makes contact with the substrate with the outer edge of each curve.

However, this form of movement is most suitable for slender or lightweight snakes, those with heavier bodies needing to use one of two other forms of locomotion. Concertina locomotion involves a heavy-bodied snake forcing its anterior body forward, using its posterior body as an anchor point, then drawing its posterior body forward, drawn by the anchored forebody, and then repeating the motion which, from above, resembled a concertina. Rectilinear locomotion, or caterpillar crawl, is used by heavy-bodied snakes like the Puff Adder (Bitis arietans) or large pythons. The entire body is held in a virtually straight line and wobbling forward progression is achieved by waves of contractions passing down the body as the ribs and intercostal muscles move forward and draw the ribs and muscles behind.

LOCOMOTION

Serpentine

Concertina

Sidewinding

Rectilinear (caterpillar crawl)

32

Locomotion

One of the most famous forms of serpentine locomotion is “sidewinding.” This is a method for moving across loose desert sand, where it is hard to gain any sort of purchase, that is employed by a number of vipers, for example, the Sidewinder Rattlesnake (Crotalus cerastes) of southwestern USA, the horned sand vipers (Cerastes spp.) of North Africa and Arabia, the Namib Viper (Bitis peringueyi) of southwest Africa, and MacMahon’s Viper (Eristicophis macmahoni) in southwestern Asia. The viper sidewinds in a series of motions that involve lifting the anterior part of the body and placing it down again a short distance away, drawing the posterior body through that point, and then repeating the process as it moves rapidly and diagonally across the sand, leaving a series of J-shaped tracks. CLIMBING

Most terrestrial snakes are excellent climbers, but there are a few extra arboreal adaptations worth mentioning. The ratsnakes and treesnakes in the Colubridae possess a ridge or keel down either side of their broad ventral scales, making them more arch-shaped rather than round in cross-section. | The Common Blunt-headed Treesnake (Imantodes cenchoa) is the ultimate tree snake. It has a long, slender, and lightweight body covered in oblique scales and with an enlarged vertebral scale row to provide rigidity when spanning gaps in the canopy. Its tail is prehensile to provide an anchorage point for security while its head is broader than the body. The catlike nocturnal eyes enable it to locate its lizard prey which is then subdued with venom from its rear fangs and swallowed. above right

| Most snakes crawl or swim using serpentine locomotion, but heavier bodied species either use concertina locomotion or rectilinear locomotion. Sidewinding is the method used by desert vipers to travel across loose sand.

When climbing a trunk they force these ridges outward, becoming almost bell-shaped as the ridges find purchases in any bark imperfections and, in this way, they can easily scale a tree or palm trunk in seconds. Many of the truly arboreal treesnakes have their dorsal scales arranged in oblique rows and, combined with an enlarged vertebral scale row for support, they are able to reach across out and bridge substantial gaps in the canopy. The most arboreal of snakes also possess a prehensile tail, which serves as an anchorage point when bridging gaps.

left

33

BURROWING

SWIMMING

There are many specialized fossorial snakes and frequently observed characteristics are pointed heads, small eyes, and short tails. One specialized fossorial family is the Uropeltidae, known as shieldtails or earthsnakes, which have an interesting method of making their burrows. The uropeltid will draw its body forward, forming the vertebrae into a series of S-shaped curves and widening the body so that it grips the burrow wall. They then force themselves forward, driving their pointed head and anterior body through the substrate until the extent of the now straightened vertebrae is reached. Then they draw the rear of the body forward and begin the process again, alternately widening and extending the burrow. Many uropeltids possess a tail that looks as if it has been cut through with a knife and a scar has formed. This is the “shieldtail,” and it often bears small hooks or rough scales, which collect soil and effectively plug the burrow behind the burrowing snake.

Many snakes swim, and most freshwater species use the same form of locomotion used on land:

34

Locomotion

serpentine or lateral undulation. Marine species like the true seasnakes and sea kraits possess laterally compressed paddle-shaped tails to aid them in swimming long distances, but the true seasnakes demonstrate a series of other adaptions that perfectly adapt them for marine life, but at the same time make them helpless on land. Sea kraits have broad ventral scales and they can move on land as well as any terrestrial snake; the true seasnakes demonstrate a reduction in these scales to the point where they are indistinguishable from the other body scales, and this enables the seasnake to laterally compress its body like a ribbon, further enhancing the swimming abilities achieved with the paddle-shaped tail. However, lacking the enlarged ventral scales, a seasnake cast up onto a beach by a storm is unable to crawl back to the ocean. The tuberculate-scaled freshwater

| A Cottonmouth (Agkistrodon piscivorus leucostoma) languidly swimming in the swamp. left

| A Paradise Flying Snake (Chrysopelea paradisi) launches itself from a tree and by spreading its body to trap the air with its convex undersides, it slows and controls its descent to the ground or another tree, but this is gliding or parachuting, not flying. above

and marine filesnakes (Acrochordus spp.) are also able to laterally compress their bodies in the same fashion for effortless swimming. GLIDING

Although there are five species of Southeast Asian snakes in the genus Chrysopelea, referred to as “flying snakes,” they do not actually fly, they glide. Due to the lack of a sternum, these snakes are able to expand their ribs outward to make their bodies wider than deep, so that when they leap from a tree to escape a predator they are able to slow their descent to the ground by trapping air in the concavity created along their undersides. They are able to control the rate and direction of their descent as a parachutist does with their canopy.

| The Bombay Shieldtail (Uropeltis macrolepis) has a tail that looks as if it has been cut through with a knife and formed a scar, but it is supposed to be like this. left

35

REPRODUCTION For the individual organism, reproduction is how it passes on its genes to future generations, and while we humans can understand the concept behind this instinct, to the rest of the animal kingdom it is just an irresistible biological drive that often overrides other concerns, like finding food or even personal safety. Mating animals, including snakes, are not only putting their lives at risk, they are also making a considerable biological investment, especially in the case of the females. And at the species level, reproduction is the means by which species adapt and evolve in response to changing environmental factors, via the process known as “survival of the fittest.” SEXUAL DIMORPHISM AND SEXUAL DICHROMATISM

When the sexes are different shapes or possess sex-specific adornments, this is termed “sexual dimorphism,” and while it is common in lizards it is much less so in the snakes. Obvious examples in snakes include the Malagasy vinesnakes (Langaha spp.), the males possessing spear-like projections on their snouts, while females exhibit something akin to a small serrated blade. Another example is the

36

Reproduction

Turtle-headed Seasnake (Emydocephalus annulatus), the male of which bears a small downwardprojecting spike on the front of its snout, while the females lack any such projection, the purpose of which will be explained (see Courtship p.37). There are also generalized dimorphisms, of course: males of many species possess broader heads and longer tails than females, to accommodate the hemipenes, while females may have relatively longer bodies, allowing more space for eggs or neonates. A few species exhibit considerable differences in overall size; for example, female Green Anacondas (Eunectes murinus) and Reticulated Pythons (Malayopython reticulatus) achieve much greater lengths and weights than male conspecifics of the same age, while the reverse is true of King Cobras (Ophiophagus hannah). When males and females are different colors this is “sexual dichromatism” and there are examples of this among the snakes. One of the most obvious is the Northern Adder (Vipera berus), males usually being pale gray with black markings, and females brown with dark brown to black markings. But, generally, sexual differences in snakes are quite subtle and an expert eye is required to determine the sex of an individual.

| The male Turtle-headed Seasnake (Emydocephalus annulatus) has a spine on his snout that he uses for courting the female. above

| Up to ten male Green Anacondas (Eunectes murinus) form a mating ball with a single receptive and much larger female. right

| The Malagasy Vinesnake (Langaha madagascariensis) exhibits sexual dimorphism, the female above and male below. far left

| Northern Adders (Vipera berus) demonstrate sexual dichromatism, the male on the left. below left

COURTSHIP

When female snakes are ready to mate they will leave a pheromonal trail, which is followed by males using their chemosensitive forked tongues. When the male encounters a receptive female he may find he is not alone, other males also having followed the same trail. As many as a dozen male Green Anacondas may form a mating ball around a much larger female in Venezuela’s Llanos wetlands, but such behavior is not limited to the large species. Paradise Flying Snakes (Chrysopelea paradisi) and Keel-bellied Whipsnakes (Dryophiops rufescens) may form continually moving “skeins” around the body of a female as they pursue her through the vegetation, and a writhing carpet of recently emerged male Red-sided Gartersnakes (Thamnophis sirtalis parietalis), awaiting the

emergence of females in the Manitoba snake pits, is a familiar serpentine image. When it comes to the actual courtship of the female, a male snake will hug her body tightly with his own and continually writhe along her back, trying to induce her to lift her tail and open her cloaca. Boas and pythons retain the remnants of the hind limbs as a pair of claw-like spurs on either side of the cloaca, and males will use these to stroke the female during courtship. Females do not reciprocate and consequentially their spurs are much smaller, or even absent. The male Turtle-headed Seasnake uses the pointed spike on his snout for the same purpose, stroking the female on the back of the neck as they swim together. 37

MALE RIVALRY

Not all males are content to share a female with other males, and some species engage in “male combat,” although the term is misleading because it suggests violence when it is usually more of an arm-wrestling exercise. Two male Northern Adders, Western Diamondback Rattlesnakes (Crotalus atrox), Black Mambas (Dendroaspis polylepis), or King Cobras (Ophiophagus hannah) may coil about one another, climbing up each other’s body as they attempt to wrestle the other to the ground without biting, in a spectacular exhibition of non-aggressive competition. However, when Reticulated Pythons engage in male combat they may use their cloacal spurs as weapons and injuries inflicted may be deep and bloody. So engrossed are the snakes in their struggle that they will often completely ignore human spectators, 38

Reproduction

just as those observers who, thrilled at getting so close to a pair of highly dangerous snakes, seem to forget that somewhere in the undergrowth lurks the object of all this activity, an adult female.

| Two male Black Mambas (Dendroaspis polylepis) wrestle for the right to mate with a nearby female. above

| A pair of mating Northern Adders (Vipera berus), the male has wrapped his tail under the female to align their cloacas while at the same time continuing to court her by wriggling along her back. right

MATING

Male snakes possess paired sexual organs known as hemipenes. When not in use, the hemipenes are retracted within the base of the male’s tail, only being extended when he mates with a female. The hemipenes are covered in an elaborate array of spines, frills, and other adornments, which are so species specific that they can be used to distinguish between males of different species. The possession of two hemipenes means a male can insert a single hemipenis into the female regardless of which side of her body he is lying beside. Snakes may copulate for long periods of time and the presence of the hemipenal adornments means it is not always easy for a male to disengage. A female adder, startled by a movement, may seek shelter and move away, dragging her male suitor backward behind her.

The male’s sperm may fertilize the female’s ova immediately, or fertilization may be delayed, some female snakes storing sperm over the winter hibernation, and there are records of sperm being stored for up to six years. Most snakes reproduce annually, but in the colder climates of Canada, Scandinavia, Patagonia, or Tasmania, when active seasons are shorter and females take longer to recover their optimum body condition, they may only reproduce every two years. Timber Rattlesnakes (Crotalus horridus) in the northern USA reproduce only every 3–4 years. A few subtropical species, living in areas with year-round prey abundance, can produce two litters per year.

39

OVIPARITY

One of the great evolutionary steps that gave reptiles their advantage over amphibians was the evolution of the amniotic egg with its protective shell and amniotic membrane. It allowed reptiles to lay their eggs on land, and negated the general amphibian requirement to return to the water to reproduce. Reproduction via external eggs containing under-developed embryos is known as “oviparity,” and the majority of living reptiles are oviparous, for example, all turtles and crocodilians; birds, which are technically avian reptiles; the tuatara; and most snakes and lizards.

40

Reproduction

Even basal mammals were oviparous, as evidenced today by the monotremes. Of the 42 snake families, 23 are fully oviparous (see Table p.43), with another four oviparous subfamilies in families that demonstrate mixed reproductive strategies. The shapes and textures of eggs vary greatly within the lizards, but all oviparous snakes lay leathery-shelled eggs, ranging in shape from ovoid to elongate. Many snakes simply lay their eggs in a hidden place where the humidity and temperature are optimal, but eggs laid in this way are subject to the vagaries of the weather and may perish.

| The baby Burmese Python (Python bivittatus) cuts a slit in the eggshell with a special egg-tooth on its front upper lip, but it may not emerge fully for some time as it absorbs the remains of the egg sac. left

| A female Diamond Python (Morelia spilota spilota) coils around her eggs, not just to protect them but also to incubate them using “shivering thermogenesis.” opposite

The female Western Grass Snake (Natrix helvetica) often lays her eggs in the same suitable location year after year, and several females may use the same site, possibly a warm compost heap in a garden; but even though grass snakes are common in England and Wales, they do not venture very far north into Scotland, the conditions being unconducive to an oviparous species. Females of some oviparous snake species are more attentive to their eggs. Pythons will coil around the clutch throughout its incubation, not just to protect the eggs from potential predators, but also to enhance incubation. A female python, a cold-blooded reptile that spends her life at the ambient temperature, can raise her body temperature during incubation by a process known as “shivering thermogenesis,” as waves of rhythmic muscular contractions pass around her body coils, resembling twitching; this muscular

activity raising her body temperature by as much as 13–23 °F (7–13 °C) above the ambient temperature. Defying the definition of being “cold-blooded,” she is effectively providing an electric blanket for her eggs. Pythons are not the only good mothers in the serpentine world. The female King Cobra uses her body coils to draw together large piles of dead vegetation into a nest. She then lays her eggs in the center and settles down to guard her nest against any threat, even elephants. When the time comes to hatch, two to three months later, the hatchling snake will escape from its egg by making a series of slits in the parchment-like shell using an egg-tooth on the front of its upper lip. The hatchling may exit the shell immediately, or it may rest awhile to absorb the remainder of the yolk sac before venturing out into the world. 41

VIVIPARITY

Females of viviparous species do not lay eggs, but instead they retain the embryos within their oviducts as they develop, where they receive nutrition from the female across fetal membranes or a placenta, the female only giving birth when her offspring are fully developed and capable of survival. Among the extant reptiles, only the Squamata (snakes and lizards) exhibit “viviparity” (live-birth), but it has evolved independently at least a hundred times within the order. Of the 42 snake families, 11 are entirely viviparous (see Table opposite). Viviparity is a risky and potentially costly strategy. A female full of offspring may not have the body space available for prey so she may not feed, and if she is killed her entire reproductive investment, and that of her mate, is lost. But viviparity also has advantages. As already mentioned, the oviparous Western Grass Snake does not occur further north than southern Scotland, but the viviparous Northern Adder occurs right up to the Highlands and also on some of the islands off the west coast of Scotland and north of the Arctic Circle in Scandinavia. The female is effectively a mobile incubator. If the weather is inclement she does not venture out, and when she does she can bask and move around as the best basking sites change with the position of the sun. Viviparity is, therefore, the best strategy for snakes living in cold environments. The Northern Adder, the northernmost snake in the world, the Patagonian Lancehead (Bothrops ammodytoides), the southernmost snake in the world, and all three species present on Tasmania, are all viviparous, as are many montane species. It is also an advantage for aquatic snakes to be viviparous. With the exception of a few specialized freshwater turtles, reptile eggs that become

42

Reproduction

inundated by water will drown. The sea kraits (Laticauda spp.) are marine snakes with flattened paddle-shaped tails, but they are oviparous and must come onto land to lay their eggs, and this requirement means they cannot venture far out into the ocean compared with the true seasnakes (Hydrophis spp. and its allies), which are viviparous and not tied to coastlines or islands. The most widely distributed naturally occurring snake in the world, the Pelagic Seasnake (Hydrophis platurus) may live its entire life out of sight of land, simply birthing its neonates directly into the ocean. Neonates are born contained within a membranous sac from which they quickly escape and become independent. Although the offspring of some species, including many vipers, remain with the female parent for a short time, and may achieve some protection that way, they are independent and must find prey and ultimately survive on their own.

REPRODUCTIVE STRATEGIES OF SNAKES

SUPERFAMILIES FAMILY

SUBFAMILY

SUPERFAMILIES FAMILY



Anomalepididae

Xenodermoidea

Xenodermidae



Leptotyphlopidae Epictinae

Pareoidea

Pareidae

SUBFAMILY

Pareinae

Leptotyphlopinae Xylophiinae Typhlopoidea

Gerrhopilidae Typhlopidae

Homalopsoidea

Afrotyphlopinae Viperoidea

Homalopsidae Viperidae

Azemiophinae

Asiatyphlopinae Crotalinae

Madatyphlopinae Viperinae

Typhlopinae Colubroidea Colubridae Chrysopeleinae

Xenotyphlopidae Colubrinae Anilioidea Aniliidae Calamariidae Tropidophiidae Grayiidae Uropeltoidea Anomochilidae Dipsadidae Carphophiinae Cylindrophiidae Dipsadinae Uropeltidae Xenodontinae incertae sedis Bolyeriidae Natricidae incertae sedis Xenophidiidae Sibynophiidae Pythonoidea Loxocemidae Pseudoxenodontidae

Pythonidae

Elapoidea

Atractaspididae

Aparallactinae

Xenopeltidae Atractaspidinae Booidea Boidae Cyclocoridae Calabariidae Lamprophiidae Candoiidae Psammophiidae Charinidae Prosymnidae Ungaliophiidae Pseudaspididae Erycidae Pseudoxyrhophiidae Sanziniidae Elapidae Elapinae Acrochordoidea Acrochordidae Hydrophiinae

All genera and species oviparous (lay eggs)

All genera and species viviparous (bear live young) Both oviparous and viviparous genera and species

| A neonate Copperhead (Agkistrodon contortrix) is born in a membraneous sac that ruptures soon after it escapes and takes its first breath. left

43

COLOR CHANGE

Some snakes have young that are differently patterned than the adults. Juvenile emerald treeboas (Corallus batesii and C. caninus) and green tree pythons (Morelia azurea and M. vidiris) have neonates and hatchlings respectively that are orange or yellow but which become green between 18 and 24 months. This is known as an ontogenetic color change. PARTHENOGENESIS

Parthenogenesis is the scientific term for virgin birth. It occurs when a female lays fertile eggs, or gives birth to neonates, without ever having mated with a male. There are two kinds of parthenogenesis. Facultative parthenogenesis is when a female of a usually sexual species produces 44

Reproduction

| Some snakes have young that are differently patterned than the adults. Juvenile Southern Green Tree Pythons (Morelia viridis) have hatchlings that are orange or yellow, but which become green between 18 and 24 months. This is known as an ontogenetic color change. left & above

| A dicephalic Cornsnake (Pantherophis guttatus), most such snakes die young but some survive to adulthood. right

offspring or eggs without contact with a mate; it might be seen as a sort of last resort in order to reproduce, and it has been recorded in boas and anacondas, pythons, filesnakes, gartersnakes, and rattlesnakes. The offspring from parthenogenetic events in boas and pythons are all female, whereas those in the filesnakes and other more advanced species are all males. The other form of parthenogenesis is obligate parthenogenesis; these species always reproduce parthenogenetically and exist as an all-female species. There are numerous obligate parthenogenetic species among the lizards across at least seven families, but there is only one obligate parthenogenetic snake species known, the Brahminy Blindsnake, or “flowerpot snake” (Indotyphlops braminus). Being able to produce

offspring without the need to find a mate makes this tiny snake a super-colonizer, and has enabled it to establish beachheads worldwide, traveling in the root-balls of horticultural or crop plants. DICEPHALISM

A snake should only possess a single head, but on occasion infant snakes are born or hatch which are dicephalic: they possess two heads at the same end of the same body. Usually these snakes do not survive long, due to other more fatal abnormalities, but sometimes they do survive and can grow to adulthood in captivity, though they are less likely to survive in nature.

45

DIET While there are lizards that occasionally, or habitually, eat vegetation, the snakes are completely carnivorous and hunt and devour a diverse range of prey species, from ants to antelope. Many snakes are euryphagous (generalist feeders), taking prey from a range of different taxonomic groups and of varying sizes, whereas others are stenophagous (specialized feeders) with very specific diets. Snakes are highly adapted predators that use their sense organs to good effect when hunting and killing prey. While some lizards, such as monitor lizards (Varanidae), are noted scavengers, whether snakes will eat carrion is a much-discussed topic. For instance, a rattlesnake seen eating a road-killed rodent could simply be following up on a prey animal it had envenomed earlier, and which had become disorientated, run

onto the road, and been hit by a vehicle. A recent video of a whipsnake (Demansia spp.) eating grapes more likely showed a snake tracking a rodent and mistakenly eating the fruit the rodent had left its scent on, perhaps by urinating on it. HOW SNAKES KILL PREY

Many snakes feed on prey that really does not fight back in any significant way. Eggs; invertebrates, like termite larvae, earthworms, and slugs, or even vertebrates such as frogs, can be consumed without the need to dispatch them first because they are unlikely to cause any damage during the swallowing process. The slime of slugs, snails, and earthworms is seemingly neutralized by oral secretions produced by specialized molluskophagous or vermivorous snakes. It seems brutal but a Western Grass Snake

| Southern African Python (Python natalensis) waits while the constriction process kills its prey, after which it will swallow the prey head first. right

| The Eastern Hognose Snake (Heterodon platirhinos) feeds on toads. When toads feel threatened they will inflate their bodies, but the enlarged rear teeth of the hognose snake will deflate the toad and oral secretions may reduce its struggles. left

46

Diet

(Natrix helvetica) has no problem swallowing a frog alive. Some toads inflate themselves as a defense and species like the hognose snakes (Heterodon spp.) quickly deflate them again using enlarged teeth positioned in the rear of the mouth. But not all prey is easy or safe to swallow alive, and snakes have evolved two systems to help them deal with more hazardous meals. The first is constriction, whereby the snake wraps its coils around the prey animal and tightens its grip until the prey is dead. Although bones may be broken in the process, crushing the prey to death is not the purpose of constriction—nor does the snake kill its prey by suffocation, preventing its lungs from obtaining air, as previously believed. Death through constriction is extremely rapid because the constricting coils are so powerful that they literally stop the flow of blood around the prey’s

body, preventing oxygen from reaching the brain and other organs, leading to unconsciousness in seconds, and death through cardiac arrest soon afterward. A version of constriction without the coiling is also used by snakes that hunt underground, such as the Eastern Indigo Snake (Drymarchon couperi). Entering a rodent burrow, it will react instantly to any prey contact so that it could easily be swallowing one rat while simultaneously pinioning and killing several others against the burrow walls, floor, and ceiling. The other method of killing prey is, of course, venom, but the delivery mechanism varies greatly from rear-fanged snakes to the front-fanged elapids and vipers (see Snake Dentition and Fangs, pp.16–17), and when does a mildly toxic oral secretion become a venom? There are venoms that cause paralysis, specifically of the 47

respiratory or neuromuscular system (pre- and post-synaptic neurotoxins, myotoxins); venoms that affect the blood and its circulation (pro- and anticoagulants, haemorrhagins, haemolycins, and platelet inhibitors); and venoms that attack tissues (cytotoxins), muscles (myotoxins again), or specifically the heart (carditoxins, sarafotoxins) or kidneys (nephrotoxins). Any particular snake venom may contain a cocktail of several of these toxin types and be finely tuned by the predator-prey arms race to deal with specific prey. A widely distributed snake species, which feeds on different prey in different countries or habitats, may exhibit significantly

different prey-specific venom compositions across its range. Venom composition may also change ontogenetically within a single individual as it matures from a juvenile feeding on lizards to a more mammalian diet as an adult. In contrast to most lizards, snakes swallow large prey whole so, for those species that prey on animals broader than their own head, the evolution of articulatable lower jaws that are not fused at the chin and spare skin in the mental groove down the center of the snake’s throat are essential evolutionary adaptations. Most advanced snakes feed on relatively large prey and they are known as “macrostomatans” (big mouths).

VENOM DELIVERY

Compressor glandulae muscle

Adductor superficialis muscle

Venom duct

Duvernoy’s gland

Venom gland

Duvernoy’s gland duct

| The venom delivery systems of front-fanged vipers and elapids are more efficient than those of rear-fanged snakes because they possess a compressor glandulae muscle to send venom to the fangs, and venom glands can store a reservoir of venom while rear-fanged Duvernoy’s glands do not. above & right

48

Diet

Adductor superficialis muscle

| Dunn’s Groundsnake (Atractus dunni) is one of legions of snakes worldwide that feed almost exclusively on earthworms and which often possess oral glands that neutralize the worm’s slimy secretions. left

INVERTEBRATE PREDATORS

A large number of snake species feed on invertebrates as juveniles, but graduate to vertebrate prey as they reach maturity. What we are concerned with here are those snakes that continue to prey on invertebrates, either totally or primarily, throughout their lives. The five families of fossorial scolecophidian blindsnakes and threadsnakes eat termite and ant eggs and larvae, entering the nests of sometimes aggressive ant species with impunity as they have smeared their close-fitting and sting-proof scales with a secretion that deters attack. These small snakes just seem to absorb eggs or larvae into their tiny mouths. Next are the “goo-eaters,” snakes that specialize in feeding on slugs and snails, the genera Sibon, Dipsas, and Tropidodipsas in the Americas, Duberria in Africa, and Pareas, Aplopeltura, and Asthenodipsas in Asia. Some of these specialist feeders possess oral glands that produce a secretion, which not only neutralizes the slimy mucus of the mollusk but also immobilizes it and facilitates its extraction from the shell, when the snake inserts one half of its lower jaw, snags the snail with its teeth, and pulls. Earthworms are common prey for many snakes that demonstrate generally catholic diets, but they

are the sole or primary prey of the shieldtails and earthsnakes (Uropeltidae), the spine-jawed snakes (Xenophidiidae), and snakes from several other families, including the Indian worm-eating snakes (Trachischium spp.), Sri Lankan roughsides (Aspidura spp.), North American wormsnakes (Carphophis spp.), and the Papuan stout-tailed snakes (Calamophis spp.). Even front-fanged venomous snakes, such as the elapids the Fiji Snake (Ogmodon vitianus) and the Papuan worm-eating snakes (Toxicocalamus), and the Uzungwe Worm-eating Viper (Atheris barbouri) feed on earthworms, while Hemprich’s Coralsnake (Micrurus hemprichii) shows a preference for velvet worms (Onychophora). There are also snakes that specialize in eating much less innocuous invertebrate prey, such as the Queen Snake (Regina septemvittata), which eats crayfish; the White-bellied Mangrove Snake (Fordonia leucobalia), which eats freshly sloughed crabs and mud lobsters; the Central American Black-ringed Centipede Snake (Scolecophis atrocinctus); and African centipede-eaters (Aparallactus spp.) and some populations of saw-scaled or carpet vipers (Echis spp.), which possess venom specifically to deal with the highly venomous scorpions they hunt. 49

| Natural pest control­—a Northern Watersnake (Nerodia sipedon) swallowing a male Round Goby (Neogobius melanostomus), which is a black color in the breeding season. This goby is an aggressive invasive in Lake Michigan. left

| A juvenile Copperhead (Agkistrodon contortrix) attracts its prey within strike range by waving its yellow tail, a behavior known as caudal luring. right

VERTEBRATE PREDATORS

Fish, ranging from gobies to catfish and eels, are the primary prey for the seasnakes and sea kraits (marine Hydrophiinae), the aquatic mudsnakes (Homalopsidae), the curious Tentacled Snake (Erpeton tentaculatum), the filesnakes (Acrochordidae), some of the watersnakes (Natricidae), African watersnakes (Grayiidae), the Annulated Water Cobra (Naja annulata) in Central Africa, the Aquatic Coralsnake (Micrurus surinamensis) in the Amazon, and the Eastern Cottonmouth (Agkistrodon piscivorus) in the USA. On Rennell Island in the Solomon Islands, the two sea kraits present partition the available resources: the endemic Lake Te-Neggano Sea Krait (Laticauda crockeri) preys on the native Dusky Sleeper, a goby (Eleotris fusca), whereas the Colubrine Sea Krait (L. colubrina), which enters the lake from the ocean, feeds on the native Pacific shortfinned eel 50

Diet

(Anguilla obscura), while neither eats the introduced Mozambique Tilapia (Oreochromis mossambicus). There are even seasnakes that specialize on fish eggs: the turtle-headed seasnakes (Emydocephalus spp.) scrape goby eggs off the coral, while the Graceful Seasnake (Hydrophis graclis) inserts its small head into the seabed burrows of gobies and vacuums up the eggs. Frogs and other anurans are favored prey of snakes at all stages of their development. The cat-eyed snakes (Leptodeira spp.) seek out and eat the eggs of treefrogs that have been laid on leaves over ponds, many aquatic snakes will gorge on tadpoles while they are available, and a wide range of snakes will take adult frogs and toads, the Yamakagashi or Tiger Keelback (Rhabdophis tigrinus) even sequestering the bufotoxins from its toad prey into its own skin and eggs to make itself and its unborn offspring both venomous and

poisonous. Salamanders and newts are preyed upon by snakes, such as the euryphagous Ringneck Snake (Diadophis punctatus), and the more stenophagous Red-bellied Mudsnake (Farancia abacura), which specializes on aquatic salamanders known as sirens (Sirenidae) and amphiumas (Amphiumidae). The limbless amphibians known as caecilians (Gymnophiona) fall prey to the South American Pipesnake (Anilius scytale) and the Red-tailed Coralsnake (Micrurus mipartitus). Some snakes, such as the Death Adders (Acanthophis spp.) and the cantils (Agkistrodon bilineatus and A. taylori) attract their prey by using a caudal lure, a yellow or white tail tip that waves about slowly to tempt frogs within range. Along with frogs, it would be expected that small lizards form a large part of the diet of numerous tropical and temperate snakes. Certainly, they form the bulk of the diets of many

desert-dwelling snakes such as sand vipers (Cerastes spp.) or the Namib Sidewinder (Bitis peringueyi), because lizards are more abundant than any other vertebrates in such environments, but a great many terrestrial and arboreal rainforest and temperate snakes are also saurophagous. The Central American Road Guarder (Coniophanes lineatus) eats venomous snakes, but it is also sometimes known by the name Lizard-Killer because it also hunts lizards. Worm-lizards (Amphisbaenia) feature strongly in the diets of fossorial and semi-fossorial snakes such as the Painted Coralsnake (Micrurus corallinus), while the Desert Coralsnake (M. tschudii) and the southern African quill-snakes (Xenocalamus spp.) feed exclusively on amphisbaenians.

51

Nothing fits inside a snake quite so well as another snake (except perhaps for earthworms, eels, amphisbaenians, and caecilians), and there are a great many snakes that occasionally or frequently devour other ophidians, a dietary behavior known as ophiophagy—it is not cannibalism unless they eat their own species, but many species, especially elapids, do that too. Notable snake-eaters include the American kingsnakes (Lampropeltis spp.), King Cobra (Ophiophagus hannah)—the clue is in the generic name—Asian kraits (Bungarus spp.), the African filesnakes (Gonionotophis, Limaformosa, and Mehelya spp.), and the Australian bandy-bandys (Vermicella spp.) The Black-headed Python (Aspidites melanocephalus) and its relative, the Woma (A. ramsayi), are desert pythons that feed on both lizards and snakes, including monitor lizards and elapids, as well as occasional mammals, and the lack of heat-sensitive pits in their labial scales hints at a primarily ectothermic diet. 52

Diet

Crocodiles might seem an unusual prey group for snakes, but there are a number of species that have managed to predate crocodilians. The Green and Yellow Anacondas (Eunectes murinus and E. notaeus) frequently prey on caimans, while Australian Olive and Water Pythons (Liasis olivaceus and L. fuscus) are known to take small crocodiles. The most famous cases involve the Burmese Python (Python bivittatus), which was accidentally introduced to Florida where they have been known to kill and eat alligators. And not to be left out, there is a case of a Puff Adder (Bitis arietans) eating a tortoise. A number of snakes specialize in eating birds. The Boomslang (Dispholidus typus) hunts chameleons but it is also an expert at entering the pendulous nests of weaver birds (Ploceidae) in order to eat their chicks. The tropical American Puffing Snake (Phrynonax poecilonotus) is another arboreal raider of bird’s nests and will endure mobbing by the parent birds in order to steal from

| Misquito Coast Coralsnake (Micrurus mosquitensis) preying on a Red Coffeesnake (Ninia sebae). opposite

| A Boomslang (Dispholidus typus) eating a helmetshrike (Prionops sp.) chick. left

| A Southern African Python (Python natalensis) may spend hours swallowing an antelope but it will not choke because it can extend its glottis (airway) out of the front of its mouth as a muscular breathing tube. below

their nests. On Chappell Island, off Tasmania, the Tigersnake (Notechis scutatus) enters the subterranean burrows of mutton birds to gorge on their chicks over a 6–8 week period, before fasting until the next breeding season, ten months away. Then there is the Brown Treesnake (Boiga irregularis) on Guam (see Feral and Invasive species, p.63). And, finally, mammals. It could well have been the explosion in early small mammal diversity 65 mya that triggered the radiation of the snakes, and today there are a huge number of ratsnakes, housesnakes, rattlesnakes, and other serpents for which a warm, furry endotherm is the ideal meal. Mice and rats breed in large numbers and snakes are the most natural predators of their legions. Bats too have their predators, in the heat-sensitive Amazonian Treeboa (Corallus hortulanus) positioned in ambush on a night-blooming Parkia plant, awaiting a nectar-feeding bat, or the pastel-colored Cave Racer (Elaphe taeniura ridleyi) hunting around bat roosts in the Batu Caves of peninsular Malaysia.

The African rock pythons (Python sebae and P. natalensis) and the Reticulated Python (Malayopython reticulatus) are giant snakes quite capable of killing and swallowing large prey, including antelope, pigs, even an adult female sun bear in the case of the latter species, and it is also these three species that have, on rare occasions, accomplished the unthinkable: they have ambushed, killed, and swallowed human beings whole. 53

DEFENSE As will be seen, snakes have many enemies, and they have evolved some ingenious ways of avoiding being eaten, some of which involve real threats, but others that are more smoke and mirrors and trickery. While some snakes announce their presence, others are truly adept at hiding in plain sight. PREDATORS AND ENEMIES OF SNAKES

Snakes may fall prey to venomous invertebrates like centipedes, spiders, scorpions, or hosts of smaller insects like army ants or yellow crazy ants, but their primary predators are among the vertebrates. Large voracious amphibians such as the Cane Toad (Rhinella marina) or African Bullfrog (Pyxicephalus adspersus) will eat snakes. The Tiger Shark (Galeocerdo cuvier) is one of the few fish that can eat highly venomous seasnakes with impunity. Snapping Turtles (Chelydra serpentina), monitor lizards (Varanus spp.), and tegus (Tupinambis spp.) can all make short work of small to medium-sized snakes, and, of course, crocodilians will also opportunistically eat snakes caught swimming. As discussed earlier, snakes may also be eaten by other snakes. Many birds will eat snakes, from the Common Buzzard (Buteo buteo) to fish eagles (Haliaeetus spp.), the Serpent Eagle (Spilornis cheela), the Secretary Bird (Sagittarius serpentarius), and the kookaburras (Dacelo spp.). Among the mammals are the obvious culprits, mongooses and meerkats (Herpestidae), but also some surprises such as the European Hedgehog (Erinaceus europaeus); however, the biggest snake killer has to be the upright ape known as Homo sapiens. The reaction of many humans upon sighting a snake is to reach for the nearest heavy 54

Defense

implement to kill it, regardless of whether the snake is dangerous or represents any kind of threat. Sometimes snakes are persecuted in huge numbers, such as in the “rattlesnake roundups” that are still permitted in some US states today. But humans also kill snakes accidentally. A stretch of warm, wet black-top might seem a great place to bask to a snake on the prowl, but increased road

| An American Bullfrog (Lithobates catesbeiana) attempting to swallow a live Florida Banded Watersnake (Nerodia fasciata pictiventris) tail-first, in Florida’s most polluted lake, Lake Apopka. above

| The East African Gaboon Viper (Bitis gabonica) has a geometric pattern of pastel colors and a head like a dead leaf that helps it blend in on the forest or woodland floor. right

building and traffic has led to rapid and clearly discernible declines in snake populations along those roads. Although snakes have no defenses against automobiles, they do have a wide range of defenses that they can use against other flesh and blood enemies. CAMOUFLAGE AND CRYPSIS

Camouflage is the art of concealing oneself from potential enemies, by adopting the color, shape, or behavior of other objects in the environment and thereby blending into the background. Crypsis is a somewhat broader term that includes mimicry, pretending to be a different and more dangerous animal, and altering one’s activity cycle to avoid predation. Many snakes are sit-and-wait ambushers, remaining motionless for hours, or days, for prey to come within strike range. For them, camouflage is useful both for avoiding giving

their presence away to their prey, and for evading detection by an enemy. A giant East African Gaboon Viper (Bitis gabonica) lies invisible in the forest leaf litter, its Persian carpet body pattern of pastel geometric designs and its large leaf-shaped head, complete with dark midvein, breaking up its outline so effectively that it is difficult to see even when you know it is there, somewhere, its only movements being its slow respiration, and the occasional flicker of its vertically elliptical pupils; the only movement, that is, until it strikes! This huge viper, 5 ft (1.5 m) long, weighing 44 lb (20 kg), fatter than a human arm, hiding 2-inch-long (5 cm) fangs inside a head almost as large as a human hand, is lying there in plain sight, yet it is virtually invisible. This is camouflage in its most effective and visceral form.

55

APOSEMATISM AND MIMICRY

While the Gaboon Viper is effectively saying “move along, nothing to see here,” the American coralsnakes (Micrurus spp.) are gaudily sending out a different message, one of “look at me, I’m patterned with warning colors so you’d better give me a wide berth”; at least, that is one interpretation of the vivid red, yellow, and black bands of these highly venomous snakes. Another possibility could be that when the semi-fossorial coralsnake is uncovered in the leaf litter, or exposed by the rolling of a log, its rapid movements and the swirling of its contrastingly colored coils may serve to confuse the uncoverer just long enough for the coralsnake to make its escape. That said, these three colors are used as warning colors by a wide variety of venomous or poisonous animals, and the bite from a coralsnake is an extremely serious accident so, perhaps, it is a bit of both: warn and confuse. Color-change is a useful defense and, while snakes are not chameleons, they can sometimes exhibit flashes of colors not normally on display, such as the black of the inside of the gaping mouth of a usually gun-metal or brown Black Mamba (Dendroaspis polylepis), the sudden flash of brilliant white in the mouth of the aptly named Cottonmouth (Agkistrodon piscivorus), or the inflation of the throat, exposing interstitial skin of a contrasting color to the scales in the Boomslang (Dispholidus typus). These are all aposematic warnings best heeded. If possessing a particular color pattern is a good way to avoid unwanted attention from potential predators, then copying those patterns should also bring an element of protection to a harmless species. This is where mimicry comes in, and a classic example would be the harmless Scarlet Kingsnake (Lampropeltis elapsoides) of southeastern USA, which mimics the pattern 56

Defense

of the venomous Eastern Coralsnake (M. fulvius) from the same geographical location. The order of the bands is important here and the famous rhyme “Red to yellow, kill a fellow; Red to black, venom lack” easily distinguishes between the two. But in Latin America there are coralsnakes with “red to black” coloration, and also mildly venomous species such as the False Coralsnake (Erythrolamprus aesculapii) to further confuse the situation. It is now believed mimicry is not as straightforward as it would initially seem to be.

| A gaping Black Mamba (Dendroaspis polylepis) shows off the contrastingly dark interior of its deadly mouth as a threat. left

| A venomous Eastern Coralsnake (Micrurus fulvius), bottom, with the warning colors arranged as “red to yellow, kill a fellow.” The harmless mimic, the Scarlet Kingsnake (Lampropeltis elapsoides), right, displaying “red to black, venom lack.”

bottom & right

57

VISUAL WARNING DISPLAYS

It has already been mentioned that a Boomslang may inflate its throat as a warning to potential enemies, and it is not alone: this is also practiced by African twigsnakes (Thelotornis spp.), neotropical puffing snakes (Phrynonax spp.), and the Tiger Ratsnake (Spilotes pullatus). But there is one very famous visual defensive display: the hooding of the cobra (Naja spp.). It is only possible for the cobra to adopt its instantly recognizable posture because of something we established in the discussion about the snake’s skeleton: snakes have no sternum (breastbone) so the ends of the ribs distal to the backbone are free and capable of being spread into the hood shape by the intercostal muscles between them. This is emphasized by the cobra rising from the ground to further intimidate its enemy and, if necessary, making short mock rushes forward, or hissing its annoyance.

58

Defense

Hooding is not confined the cobras: it has also evolved in the King Cobra (Ophiophagus hannah) and the Asian mock cobras (Pseudoxenodon and Plagiopholis spp.), the African coralsnake (Aspidelaps lubricus), Australian blacksnakes (Pseudechis spp.), and the South American False Water Cobra (Hydrodynastes gigas), so clearly the sight of a snake raising up to a third of its body off the ground and spreading a hood is internationally viewed as a threat posture. Such an effective warning is the cobra’s hood that it is believe that Slow Lorises (Nycticebus spp.) mimic them by raising their arms over their head to make the shape of the hood, their own large eyes recreating the markings of the cobra. AUDIBLE WARNING DISPLAYS

Obviously, the most basic audible warning a snake can issue is a long drawn-out hiss, especially the loud, long, intimidating hisses of the Russell’s

vipers (Daboia russelii and D. siamensis) or the the Puff Adder (Bitis arietans), or even that of Bull Snake (Pituophis catenifer). Common cobras in Asia seem to have two different hisses: a short “I’m irritated” tst-tst-tst, and the more threatening, more drawn out “Now I’m serious” hiss. Large King Cobras are said to utter a deep growl as a warning. But hissing is a costly business. Every time a snake hisses it expels a breath of air, and with that air, moisture. That does not matter in a humid rainforest, but in a particularly arid habitat like desert it might be better to find an alternative and less water-costly means of making a sound. The Copperhead (Agkistrodon contortrix) of eastern North America will warn off intruders by vibrating its tail on dead leaves in its woodland home. In the absence of dead leaves, the rattle of a rattlesnake (Crotalus spp.) is a marvelous adaptation and the reason they are often called

“buzztails.” A neonate rattlesnake bears a tiny button on the end of its tiny tail, and although it may rattle its tail, at this point it makes no sound. But every time the snake sheds its skin it adds a link to the proximal end of its rattle until, over time, it grows a multi-linked rattle that will produce an audible and instantly recognizable sound when shaken rapidly by specialized muscles in its tail. To debunk a myth, you cannot age a rattlesnake by the number of links because they are added at irregular intervals as it grows, and long rattles are fragile and prone to breaking.

| The Indian Cobra (Naja naja) is one of the most instantly recognizable snakes because of its spectacle-marked hood. far left

| The first stage in the threat of a twigsnake (Thelotornis spp.) is to inflate its neck, the next is to flatten its head like a lance. There is no antivenom for its bite should these postures be ignored. left

| This Tiger Rattlesnake (Crotalus tigris) has a nine-link rattle with which it will produce that familiar warning sound. Composed of dry skin, with a link added every time the snake sloughs, there is nothing inside the rattle (inset), each link fits loosely into the two previous links so that any movement of the tail will cause them to rattle together. right

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Rattlesnakes are endemic to the Americas so there are none in Asia or Africa, but there are snakes there that issue a similar warning sound, the carpet or saw-scale vipers (Echis spp.). These small but highly venomous snakes exhibit an unusual arrangement of the dorsal scale rows along their flanks: they are arranged more obliquely than the scales on the dorsum of the back, and each of the scale keels is finely serrated. When the saw-scale viper feels threatened it will form its body into a series of concentric curves, while maintaining its head to the front. It will then begin to move backward, away from the threat; but, as its coils move against one another the serrated scales make a rasping, sawing sound, aptly warning that to approach within the range of the little viper’s jabbing strike would be a foolish move, even for a large predator. Perhaps the strangest sound-making is that of the Sonoran Coralsnake (Micruroides euryxanthus), which engages in cloacal-popping, expelling air from its cloaca; though how effective a warning it is must be open to question. 60

Defense

| Saw-scale and Carpet Vipers (Echis spp.) have specially arranged serrated rows of scales on their flanks so that when they rub their concentric body coils together they make a sawing sound. left

| The Sonoran or Arizona Coralsnake (Micruroides euryxanthus) has warning colors, but it also raises its tail and makes a popping sound with its cloaca. above

| A Mozambique Spitting Cobra (Naja mossambica) sending a cloud of venom toward a perceived enemy. right

| This Iberian Grass Snake (Natrix astreptophora) is playing dead, a behavior known as thanatosis. far right

OTHER TACTICS

There are many fast-moving diurnal snakes that earn the names “whipsnake” (Masticophis in North America, Demansia in Australia) or “racer” (Coluber in North America, Platyceps in Eurasia), and all these species, and more, put their speed to good use when fleeing a potential predator. Other snakes adopt the exact opposite tactic: they stay where they are and play dead, a behavior known as thanatosis, rolling on their backs with their tongues lolling out, presumably only a successful technique if the threat is not a scavenger that eats carrion. The Ringhals Spitting Cobra (Hemachatus haemachatus), American hognose snakes (Heterodon spp.), and the grass snakes (Natrix spp.) are all well known for this behavior. Among a disparate array of defenses, perhaps one exemplifies the notion that attack is the best form of defense. The spitting cobras (Naja spp.) possess specially adapted fangs that enable them to send twin jets of venom into the face of their perceived aggressor. While the venom of non-spitting cobras is primarily neurotoxic in

composition, that of the spitters is more cytotoxic, breaking down the tissues. When it lands in the eyes of an animal it will start to digest the corneas, causing pain and blindness, and providing the cobra with sufficient time to escape. Many spitting cobras do not even bother with Plan A, raising a hood, going straight to Plan B, spitting when they are only slightly raised off the ground. The venom can be washed from the eyes fairly easily by prolonged bathing with water, but the victim needs to be human to know that. Once they have immobilized their enemy they will effect a rapid escape rather than coming in close for the coup de grâce. Interestingly, spitting cobras do not seem to spit when hunting.

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CONSERVATION Many people do not like snakes. That is an unfortunate global reality. But whether their feelings are based on the fear of snakebite, a rational and very real danger for millions of people in the tropics, or on a more irrational revulsion, born out of one of the many myths about snakes, that they are slimy to the touch, for instance, there is no getting away from the fact that snakes have a public relations problem. But whether snakes are actively persecuted, or are threatened by the same factors that impact other wildlife, such as habitat loss, road building, climate change, or pollution, they are still in need of protection, of conservation. Three billion people, half the world’s population, rely on the rice crop to survive. But rice crops also attract legions of rodents which are responsible for losses of 5–10 percent of the rice, with increases in some areas to 20 percent, 30 percent, even 50 percent. These same rodents pass on diseases such as Weil’s disease through their

urine, and Lyme disease from the bites of ticks living on the rodents. Snakes are the number one most effective rodent exterminator and they should be encouraged, not discouraged or killed, when encountered living in rice-paddies or plantations of other crops. RATTLESNAKE ROUNDUPS

In some tropical countries, snakes are also harvested in unsustainable numbers for their skins, meat, and their gall bladders, this last for an unproven tonic for a failing libido. But they are also severely threatened by western practices. Rattlesnake roundups were started in some US states to remove snakes that were considered a threat to cattle, but over time they have turned into multimillion-dollar entertainment, with thousands of rattlesnakes being collected annually, even shipped in from out of state to keep up with demand. At one time the snakes were slaughtered during or after the events,

| Rattlesnakes at the world’s largest roundup at Sweetwater, Texas. This is not the best way to educate this young lad to appreciate nature. above

| The Brown Treesnake (Boiga irregularis) is at equilibrium within its native range but on Guam it has caused an ecological catastrophe. left

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Conservation

but today some (but not all) organizers claim they release snakes back into the wild, and that the roundups are intended to be educational. But rattlesnakes are now thought to grow up knowing their own neighborhoods, and just dumping them into the wild somewhere else, often stressed and in poor condition, does not bode well for their orientation and survival. And with the burgeoning problem of Snake Fungal Disease (SFD) in native US snake populations, the holding together and subsequent release of thousands of stressed snakes back into nature is akin to a super-spreader event, introducing the fungal pathogen to wild populations where it may not have formerly been present. FERAL AND INVASIVE SPECIES

When this subject was covered in Lizards of the World, the emphasis was on the damaging effect that introduced mammals, such as cats, rats, goats, and pigs had on the native lizard faunas, especially those on remote islands. Island snake faunas are also threatened by domestic or invasive animals. For instance, the remotest terrestrial elapid snake in the world, Ogmodon vitianus, locally known as gata ni balabala (snake

of the mountain ferns), but referred to more widely as the Fiji Snake, is a snake on the brink. This tiny (< 12½ in/320 mm), semi-fossorial snake is only found on the southern side of Viti Levu, Fiji’s main island, 1,200 miles (2,000 km) from its next nearest terrestrial elapid relative, in the Solomon Islands. Close to the evolutionary origins of Australasian elapids, but considered harmless, Ogmodon is threated by the activities of semi-feral village pigs, which root in the soil and will quickly devour any snake uncovered. This unique snake is now listed as Endangered by the International Union for Conservation of Nature (IUCN). If that circumstance seems remote, then consider a recent survey of southern Belgian populations of the Northern Adder (Vipera berus) that demonstrated that they are under severe threat from wild boar populations, which are growing rapidly in the absence of predators and the prohibition of hunting. A similar situation may also be occurring with the adder population in the Forest of Dean in the UK, where introduced wild boar have become established and are also protected. But it is impossible to discuss invasive wildlife and not mention that snakes can be the culprits too. The most famous example was the accidental relocation of the Brown Treesnake (Boiga irregularis) from New Guinea to the Pacific island of Guam with returning US military equipment, after World War II. This voracious and highly arboreal predator found itself on an island inhabited by birds that had never encountered snakes before, some of them flightless species, and the treesnake promptly ate seven species to extinction, with three more, including the endemic Guam Rail (Hypotaenidia owstoni) being placed into protective custody as the snake populations rose to over a million and scientists struggled to find a way to fight the invasion. On a smaller scale, 63

the Island Wolfsnake (Lycodon capucinus) and Common Wolfsnake (L. aulicus), both lizard predators, have become established on Pacific and Indian Ocean islands and may have been part of the reason for lizard extinctions and extirpations in countries like Mauritius. On a much larger scale, the release of many juvenile Burmese Pythons (Python bivittatus) into southern Florida, whether by a hurricane or by humans, has caused an environmental catastrophe as the pythons grew to over 16 ft (5 m) and began to breed and colonize the sawgrass habitat, not dissimilar to their native Asian riverine grasslands. No longer is the American Alligator (Alligator mississippiensis) the unassailable climax predator, because pythons have been found with the remains of alligators in their stomachs. Under greater threat are endangered waterbirds and rare mammals like the already endangered Key Largo Woodrat (Neotoma floridana smalli). SNAKE EXTINCTIONS AND CONSERVATION PROJECTS

Round Island is a tiny (0.65 square miles/1.69 square kilometers) uninhabited islet 14 miles (22.5 km) north of Mauritius, itself an isolated Indian Ocean country. Round Island is home to a number of endemic animals and plants that may once have also inhabited Mauritius. In 1957, recognizing the importance of Round Island, the Mauritian authorities launched a conservation program to protect its fauna and flora, beginning with the eradication of invasive goats and rabbits. 64

Conservation

| The Antiguan Racer (Alsophis antiguae) is an example of how a conservation program involving captive breeding can save a species from extinction. above

| Up to 3,000 Burmese Pythons (Python bivittatus) are captured annually in southern Florida. right

In 1976, the Jersey Wildlife Preservation Trust (JWPT) got involved and set up successful captive breeding programs for the endangered reptile fauna, comprising two skinks, three geckos, and a snake, the Round Island Keel-scaled Boa (Casarea dussumieri). But the rescue came too late for the Round Island Burrowing Boa (Bolyeria multocarinata), which has not been seen since 1975 and is listed as Extinct by the International Union for the Conservation of Nature (IUCN). Another rescue project is underway on Christmas Island, an Australian External Territory just south of western Java, which has been used for phosphate mining, currently houses an immigration center for asylum seekers, and was also utilized as a quarantine center for returning Australians in the early days of the Covid-19 crisis. The main threat to the island’s fauna was caused by the accidental introduction of the invasive Asian Yellow Crazy Ant (Anoplolepis gracilipes), which will kill small vertebrates. Of the four endemic lizards, one is Extinct, two are Extinct in the Wild, and one is Endangered, as is

the Christmas Island Blindsnake (Ramphotyphlops exocoeti), according to the IUCN. The Caribbean has witnessed a number of snake extinctions including the Barbados Racer (Erythrolamprus perfuscus) and the St. Lucia Cribo (Clelia errubunda), but one resounding success is the JWPT captive breeding and reintroduction program for the Antiguan Racer (Alsophis antiguae). And other snake species have proven themselves to be “Lazarus species.” Cropani’s Boa (Corallus cropanii) was thought to have gone extinct in the Atlantic coastal forests of Brazil in 1954, but a specimen was found alive and well in 2017 and is now being radiotracked. Similarly the Autlán Long-tailed Rattlesnake (Crotalus lannomi) was thought possibly extinct in Mexico as only the type-specimen, collected in 1966, was known, but in 2008 a living specimen was found. Extinction is a negative and it is often hard to prove a negative. The famous quote states: “Absence of evidence is not evidence of absence,” so it is hoped that more Lazarus species will be found. Sadly it is too late for the Round Island Burrowing Boa. 65

THE SNAKE INFRAORDERS AND SUPERFAMILIES

| The majestic King Cobra (Ophiophagus hannah) is the “King of Snakes,” though strictly it is not actually a cobra. below

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While there are six lizard infraorders, there are only two for snakes. The Scolecophidia (wormsnakes) contains the five families of blindsnakes and threadsnakes, three of which are placed in a single superfamily, Typhlopoidea. The second infraorder is the Alethinophidia (true snakes) which is itself divided into two clades, the Amerophidia and the Afrophidia, effectively the “not out of America” and “out of Africa” groups depending on their origins. The Amerophidia contains two families that did not spread further than Central and South America, and the Caribbean, while the Afrophidia contains all other known snakes. The basal Afrophidia are the Henophidia (old snakes), containing three superfamilies with 15 families, although two of these families are incertae sedis (of unknown placement) and not allocated to a superfamily. The remainder of the Afrophidia is included in the Caenophidia (advanced snakes) and comprises seven superfamilies and 20 families, containing the bulk of the world’s snake species. These higher taxonomic categories are always in a state of flux with what constitutes a family or subfamily a continual source of debate and change. Eight of the caenophidian families have been elevated from subfamily status since 2018.

SCOLECOPHIDIA ANOMALEPIDIDAE

LEPTOTYPHLOPIDAE

TYPHLOPOIDEA TYPHLOPIDAE GERRHOPILIDAE XENOTYPHLOPIDAE

ALETHINOPHIDIA AMEROPHIDIA

ANILIOIDEA ANILIIDAE TROPIDOPHIIDAE

AFROPHIDIA HENOPHIDIA

CAENOPHIDIA

UROPELTOIDEA ANOMOCHILIDAE CYLINDROPHIIDAE UROPELTIDAE

ACROCHORDOIDEA ACROCHORDIDAE

incertae sedis BOLYERIIDAE incertae sedis XENOPHIDIIDAE PYTHONOIDEA XENOPELTIDAE LOXOCEMIDAE PYTHONIDAE BOOIDEA CALABARIIDAE SANZINIIDAE CHARINIDAE UNGALIOPHIIDAE BOIDAE ERYCIDAE CANDOIIDAE

COLUBROIDEA COLUBRIDAE CALAMARIIDAE GRAYIIDAE SIBYNOPHIIDAE PSEUDOXENODONTIDAE NATRICIDAE DIPSADIDAE ELAPOIDEA LAMPROPHIIDAE PSAMMOPHIIDAE PROSYMNIDAE CYCLOCORIDAE PSEUDASPIDIDAE PSEUDOXYRHOPHIIDAE ATRACTASPIDIDAE ELAPIDAE PAREOIDEA PAREIDAE XENODERMOIDEA XENODERMIDAE HOMALOPSOIDEA HOMALOPSIDAE VIPEROIDEA VIPERIDAE

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SCOLECOPHIDIA: SUPERFAMILY TYPHLOPOIDEA The etymology of Scolecophidia is scolec = worm, -ophidia = snake, so named because these small snakes are long, slender, and subterranean. Most are called blindsnakes although they do possess eyes, albeit reduced to photosensitive cells, under translucent head scales, that warn the snake when exposed to the light. There are five families. The Anomalepididae (early blindsnakes) is Latin American; the Leptotyphlopidae (threadsnakes) inhabit the Americas, Africa, and Western Asia; the Typhlopidae (cosmopolitan blindsnakes) are distributed worldwide; the Gerrhopilidae (glandular blindsnakes) occur from India to the western Pacific; and the Xenotyphlopidae is endemic to Madagascar. The divergence between the Typhlopidae and Leptotyphlopidae occurred in Gondwanaland in the Early Cretaceous (139 mya). The families Typhlopidae, Gerrhopilidae, and Xenotyphlopidae are closely related in the superfamily Typhlopoidea, which excludes Leptotyphlopidae and Anomalepididae. The five families contain 40 genera and 463 species, almost 11.7 percent of all living snakes. With a few exceptions, these snakes are little studied due to their secretive nature and small size. One species, Indotyphlops braminus, is encountered around the world; because it is an obligate parthenogen, only females exist, and they reproduce without a male. At least 25 lizard species across seven families utilize this strategy, but only one snake, and its ability to reproduce parthenogenetically has enabled it to colonize much of the world and become the most widely distributed, non-naturally occurring, snake species in the world.

| The Southern Blindsnake (Anilios australis) from southwestern Australia, is one of 47 Anilios found in Australia. left

ANOMALEPIDIDAE

EARLY BLINDSNAKES | The Whitenosed Early Blindsnake (Liotyphlops albirostris) is named for its white snout, but many anomalepids have white heads. opposite

| The Trinidad Early Blindsnake (Typhlophis squamosus) is also found on mainland South America. below

he early blindsnakes or dawn blindsnakes, are included in the endemic neotropical family Anomalepididae, and comprise four genera and 21 species. Believed to be the most basal of all living snakes, anomalepids possess teeth on both the maxillary (upper jaw) and dentary (lower jaw, one to three teeth), unlike typhlopids, gerrhopilids, and xenotyphlopids (teeth only on maxillary bones) and leptotyphlopids (teeth only on dentary bones). They possess specially adapted skulls for burrowing but lack any vestiges of hind limbs. They also lack a left lung, but possess a tracheal lung, and a functioning left oviduct. The two centers of anomalepidid radiation are northwest Colombia and southwest Brazil, both of which contain nine species, many of them endemic. The genus Anomalepis, the Pacific coastal early blindsnakes, occurs from Colombia to Ecuador and Peru, with the Central American Early Blindsnake (A. mexicanus) occurring farther north to Honduras, but not Mexico.

distribution

size

reproduction

South America, southern Central America, and Trinidad

TTL 5¾ in (146 mm) Ecuadorian Dawn Blindsnake (Anomalepis flavapices) to 15¾ in (395 mm) Bogota Dawn Blindsnake (Liotyphlops anops)

Oviparous with clutches of 2–24 eggs

genera

Anomalepis, Helminthophis, Liotyphlops, and Typhlophis habitats

Lowland rainforest

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T

activity

Fossorial

SCOLECOPHIDIA—Superfamily Typhlopoidea

diet

Ant and termite eggs and larvae, earthworms, caecilians, amphisbaenians

Genus Helminthophis contains three species of Caribbean early blindsnakes from Colombia, Venezuela, Panama, and Costa Rica, including the Yellow-tailed Early Blindsnake (H. flavoterminatus). The monotypic Trinidad Early Blindsnake (Typhlophis squamosus) also occurs on the South American mainland, from Guyana to northern Brazil. The largest genus is Liotyphlops, with 13 species of Atlantic early blindsnakes centered on Colombia and Brazil but also occurring north to Costa Rica and south to northern Argentina, the southernmost species being Ternetz’s Early Blindsnake (L. ternetzii).

The Caiçara Early Blindsnake (L. caissara) is endemic to two small islands, Ilha Anchieta and Ilha de São Sebastião, off the Atlantic coast of São Paulo, Brazil. Anomalepidids are relatively understudied although five species of Liotyphlops have been described since 2000. Small and slender, they are found in ants’ nests, termite mounds, and rotten logs or palm trunks, where they prey on ant and/or termite eggs and larvae. They are oviparous producing up to 15 small leathery-shelled eggs.

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LEPTOTYPHLOPIDAE—EPICTINAE

SHORT-TAILED THREADSNAKES

T

he leptotyphlopids are the threadsnakes, generally smaller and more slender than the typhlopids. The world’s smallest snake, the Barbados Threadsnake (Tetracheilostoma carlae), belongs here. Only known from three specimens, it achieves a total length of only 4 in (100 mm). Leptotyphlopids possess four to five teeth on their dentary bones. Although they have a large functional right lung, they lack a tracheal lung. Two subfamilies are recognized: the short-tailed Epictinae and the long-tailed Leptotyphlopinae.

The Epictinae comprises ten genera and 88 species across tropical America and Africa. The largest genus is Epictia (44 species), found from Mexico and the Caribbean to Argentina. The brightly colored Three-colored Threadsnake (E. tricolor) occurs up to 10,700 ft (3,250 m) in Peru. Genus Mitophis (four species) is endemic to the Caribbean island of Hispaniola, while Tetracheilostoma (three species) inhabits the Lesser Antilles. Other South American genera include Siagonodon (three species), Trilepida (14 species), and the

EPICTINAE

habitats

distribution

Rainforest, also woodland, savanna, agricultural habitats, and desert

Southwestern USA, Mexico, Central America, South America, Hispaniola, Bahamas, Lesser Antilles, Dutch Antilles, and West and Central Africa genera

Epictia, Habrophallos, Mitophis, Rena, Rhinoleptus, Rhinoguinea, Siagonodon, Tetracheilostoma, Tricheilostoma, and Trilepida

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SCOLECOPHIDIA—Superfamily Typhlopoidea

size

TTL 3¾ in (93 mm) Barbados Threadsnake (Tetracheilostoma carlae) to 18 in (460 mm) Koniagui Threadsnake (Rhinoleptus koniagui)

monotypic Collared Threadsnake (Habrophallos collaris). The northernmost genus is Rena (11 species), with four species in southwestern USA, including the Texas Threadsnake (R. dulcis), | The Southwestern Threadsnake (Rena humilis) is one of several threadsnakes that inhabit aggressive ant nests in southwestern USA. above

| The Collared Threadsnake (Habrophallos collaris) is a monotypic species from the Guianan region. left

activity

Fossorial reproduction

Oviparous with clutches of 1–15 eggs diet

Ant and termite eggs and larvae, other soft-bodied invertebrates

which occurs in small aggregations, and Western Threadsnake (R. humilis). Genus Rena also occurs as far south as Argentina. The West African epictines include two monotypic species, the 15¾ in (398 mm) Mali Threadsnake (Rhinoguinea magna) and the largest leptotyphlopid, the 18 in (460 mm) Koniagui Threadsnake (Rhinoleptus koniagui). A third African genus, Tricheilostoma (six species) occurs from Guinea to Sudan. Their distribution on both sides of the Atlantic is believed due to an ancestral divergence 74 mya, when Africa and South America were just separating. Most epictine species are rainforest inhabitants, but Rena inhabits arid grassland and desert in Mexico and USA, where they are often found in the nests of aggressive ants. Covering their tight-fitting scales with a cloacal solution, they deter any attack and can devour ant larvae at a rate of one per minute.

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LEPTOTYPHLOPIDAE—LEPTOTYPHLOPINAE

LONG-TAILED THREADSNAKES

T

he long-tailed threadsnakes of the Leptotyphlopinae are primarily African but also occur on the Arabian Peninsula and in Western Asia. Their ancestors are believed to have diverged from the ancestors of the Epictinae some 74 mya when a sea divided southern and eastern Africa from western Africa. The difference in tail length between the two subfamilies is not absolute: tails of leptotyphlopines are 4.1–18.9 percent of total

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length, whereas those of the epictines are 2.1–11.5 percent of total length. The Leptotyphlopinae contains four genera and 53 species. The nominate genus, Leptotyphlops (21 species), is distributed from the Horn of Africa to the Cape of Good Hope and on inshore Indian Ocean islands, for example the Pemba Island Threadsnake (L. pembae). The largest genus Myriopholis (24 species) is also the most widely distributed, recorded from

LEPTOTYPHLOPINAE

habitats

activity

distribution

Africa, Arabian Peninsula, Western Asia, and Socotra

Desert and semidesert, also savanna, woodland, rainforest, and agricultural habitats

Fossorial

genera

size

Epacrophis, Leptotyphlops, Myriopholis, and Namibiana

TTL 4 in (100 mm) Socotran Threadsnake (Myriopholis wilsoni) to 12¾ in (322 mm) Western Threadsnake (Namibiana occidentalis)

SCOLECOPHIDIA—Superfamily Typhlopoidea

reproduction

Oviparous with clutches of 1–7 eggs diet

Ant and termite eggs and larvae, other soft-bodied invertebrates

| The Hook-nosed Threadsnake (Myriopholis macrorhyncha) occurs across North Africa and western Asia and is probably a species complex. Like many desert-dwelling species it is pink in color. above

| The Damara Threadsnake (Namibiana labialis) inhabits northern Namibia and southern Angola. left

40 of the 49 mainland African countries, the Arabian Peninsula, and western and southern Asia. The most widely distributed species is the Hook-nosed Threadsnake (M. macrorhyncha), found from Algeria to India, but almost certainly a complex of morphologically identical species. Many species exhibit localized ranges; the Yemeni island of Socotra, for example, at 1,390 sq mile (3,600 sq km), almost the same size as Long Island,

New York, has three endemic Myriopholis, including the smallest leptotyphlopine, Wilson’s Threadsnake (M. wilsoni), at 4 in (100 mm) in length. The other genera in the Leptotyphlopinae are much smaller and more localized in their distribution. Genus Epacrophis (three species) inhabits Somalia and Kenya, while Namibiana (five species) is found in Namibia, Angola, and South Africa. The largest leptotyphlopine is the 12¾ in (322 mm) Western Threadsnake (N. occidentalis) from Namaqualand. Long-tailed threadsnakes are primarily species of arid open habitats, such as savanna grassland or semidesert. Desert species such as Nurse’s Threadsnake (M. nursii), from the Arabian Peninsula, are not dark, but pale brown or pink to blend in with the sandy substrate.

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TYPHLOPIDAE—ASIATYPHLOPINAE

ASIAN BLINDSNAKES

T

he Typhlopidae (cosmopolitan blindsnakes) is the largest and most widely distributed scolecophidian family, with 18 genera and 277 species. Typhlopids possess teeth on their maxillary bones only, and a tracheal lung. In general, they are larger and stouter than leptotyphlopids and although there are some small typhlopids there are also some giants.

In 2014 the cumbersome Typhlopidae was divided into four geographical subfamilies, based on molecular data. The largest of these is the Asiatyphlopinae, with nine genera and 132 species, distributed from southeastern Europe to eastern Asia, Australia, and the Pacific region. This subfamily contains the Brahminy Blindsnake, or “flowerpot snake” (Indotyphlops braminus), the

ASIATYPHLOPINAE

habitats

distribution

Rainforest, woodland, grassland, desert, semidesert, and agricultural gardens

Southeastern Europe; South, Southeast, and Western Asia; Melanesia; western Pacific; and Australia; also Socotra and Mauritania genera

Acutotyphlops, Anilios, Argyrophis, Cyclotyphlops, Grypotyphlops, Indotyphlops, Malayotyphlops, Ramphotyphlops, Sundatyphlops, and Xerotyphlops

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SCOLECOPHIDIA—Superfamily Typhlopoidea

size

TTL 1¼ in (31 mm) Malcolm’s Blindsnake (Indotyphlops malcolmi) or Violet Blindsnake (I. violaceus) to 29½ in (750 mm) Woodland Blindsnake (Anilios proximus) or Black Blindsnake (A. nigresens)

| The Eurasian Blindsnake (Xerotyphlops vermicularis) is Europe’s only scolecophidian. It occurs in Greece and the southern Balkans, and through Turkey to Iran and Afghanistan. right

| The monotypic Lesser Sunda Blindsnake (Sundatyphlops polygrammicus) contains five subspecies: S. p. polygrammicus on Timor, S. p. brongersmai on Sumba, S. p. elberti on Lombok, S. p. florensis on Flores, and S. p. undecimlineatus on Sumbawa and Komodo. This is the Timor subspecies. left

only parthenogenetic snake that has managed to colonize much of the tropical and subtropical world, carried in the root-balls of horticultural or agricultural plants. Genus Indotyphlops (23 species) is South Asian but also occurs east to Hong Kong and south to Komodo, Flores, and Timor, overlapping with the Indo-Chinese Argyrophis (13 species); Ramphotyphlops (22 species) is found through Indonesia and New Guinea, eastwards to Fiji; and Malayotyphlops (12 species), despite its name, is a Philippine and Indonesian genus.

activity

Fossorial, semi-arboreal reproduction

Oviparous with clutches of 1–14 eggs (one parthenogenetic species) diet

Ant and termite eggs and larvae, soft-bodied invertebrates, earthworms

There are no leptotyphlopids in Australasia, but it is here that typhlopids demonstrate their greatest diversity with Anilios (48 species) adapted to habitats from arid Australian deserts to New Guinea rainforests. Genus Xerotyphlops (six species) includes the Eurasian Blindsnake (X. vermicularis) of southeastern Europe. There are also some interesting monotypic genera, such as the Indian Beaked Blindsnake (Grypotyphlops acutus), a large and widespread South Asian species; the Lesser Sunda Blindsnake (Sundatyphlops polygrammicus), with five island subspecies; and the strange and rarely seen Sulawesi Blindsnake (Cyclotyphlops deharvengi), which exhibits a large round scale on top of its head. Most blindsnakes feed on ant and termite eggs and larvae, but the sharp-nosed blindsnakes, genus Acutotyphlops (five species), of the Solomon Islands, Bougainville, the Bismarck Archipelago, and the Philippines are large snakes (13–17¾ in/330– 450 mm) that feed on earthworms.

77

TYPHLOPIDAE—AFROTYPHLOPINAE AND MADATYPHLOPINAE

AFRICAN AND MADAGASCAN BLINDSNAKES

T

he Afrotyphlopinae contains 71 species in three genera, while the Madatyphlopinae contains a single genus (Madatyphlops). The Afrotyphlopinae is distributed throughout subSaharan Africa, from the Horn of Africa to the Cape of Good Hope. Genus Afrotyphlops (28 species) comprises stout and relatively large blindsnakes with rounded or pointed snouts and eyes that are visible as round dark spots under translucent scales. Found throughout Africa,

it includes the largest blindsnakes, for example, Schlegel’s Giant Blindsnake (A. schlegeli), at 35½ in (900 mm) and the Zambezi Giant Blindsnake (A. mucruso) at 37½ in (950 mm), but also small species, such as the Kenyan Dwarf Blindsnake (A. nanus) at 5 in (125 mm). Some species are found in the Gulf of Guinea, namely the Blotched Blindsnake (A. congestus) and Spotted Blindsnake (A. punctatus) on Bioko Island and the endemic Principe Island Blindsnake (A. elegans). The largest species live deep underground

| Delalande’s Beaked Blindsnake (Rhinotyphlops lalandei) is a widespread arid habitat species from southern Africa. right

| The Zambesi Giant Blindsnake (Afrotyphlops mucruso) is the largest blindsnake, achieving almost 3 ft 3 in (1 m) in length and a girth as stout as a cigar. It is only seen above the surface after heavy rain. left

AFROTYPHLOPINAE

habitats

activity

distribution

Rainforest, woodland, savanna and semidesert

Fossorial

size

Oviparous with clutches of 2–60 eggs

Sub-Saharan Africa, also southern Turkey, Israel, Jordan, and Lebanon (red area) genera

Afrotyphlops, Letheobia, and Rhinotyphlops

78

TTL 5 in (125 mm) Kenyan Dwarf Blindsnake (Afrotyphlops nanus) to 37½ in (950 mm) Zambezi Giant Blindsnake (A. mucruso)

SCOLECOPHIDIA—Superfamily Typhlopoidea

reproduction

diet

Ant and termite eggs and larvae, soft-bodied invertebrates

and store fat reserves to enable them to survive long periods without food. These blindsnakes may be dark or bicolored, with dark above and light below. Genus Letheobia (36 species) contains slender blindsnakes, which may be pale pink in color, although some species are dark. The eye spots of Letheobia species are smaller and less visible, and may even be invisible. Most Letheobia species are sub-Saharan African, but Bischoff’s Blindsnake (L. episcopus) inhabits Turkey, while the Israeli Blindsnake (L. simoni) is found in the Levant region.

MADATYPHLOPINAE distribution

Madagascar (blue area) genus

Madatyphlops habitats

Rainforest, dry forest, thorn scrub, and coastal sand dunes size

TTL 7 in (176 mm) Domergue’s Malagasy Blindsnake (Madatyphlops domerguei) to 23¾ in (600 mm)

Island species are found on Zanzibar and Pemba in the Indian Ocean and São Tomé Island in the Gulf of Guinea. The third genus, Rhinotyphlops, contains seven East and Southern African species with hooked beaks for burrowing. One of the most distinctive is Delalande’s Beaked Blindsnake (R. lalandei), which is dark pink with a shovel-shaped snout. The subfamily Madatyphlopinae comprises a single genus, Madatyphlops, with 13 species on Madagascar, one on the Comores islands, and one on the French Indian Ocean island of Mayotte.

Decorse’s Malagasy Blindsnake (M. decorsei) activity

Fossorial, semi-arboreal reproduction

Oviparous, clutch sizes unknown diet

Presumed ant and termite eggs and larvae

79

TYPHLOPIDAE—TYPHLOPINAE

AMERICAN BLINDSNAKES

T

he Typhlopinae is represented by four genera and 59 species. The genus Typhlops, which at one time contained all typhlopid blindsnakes, has been redefined to include just 20 species from the Greater Antilles: Hispaniola (13 species), Cuba (four species), and one species each from Jamaica, Puerto Rico, and the Bahamas. | The Earthworm Blindsnake (Typhlops lumbricalis) is a widespread Bahamian species that may represent a species complex. below

TYPHLOPINAE

habitats

activity

distribution

Rainforest, grassland, desert, semidesert, and islands

Fossorial, semi-arboreal

size

Oviparous with clutches of 1–10 eggs

Southern Mexico, Central and South America, West Indies, Greater and Lesser Antilles, and Bahamas genera

Amerotyphlops, Antillotyphlops, Cubatyphlops, and Typhlops

80

Genus Cubatyphlops (12 species) is centered on Cuba, but two species each occur on the Cayman Islands and in the Bahamas. The genus Antillotyphlops (12 species) inhabits the eastern Greater Antilles and the northern Lesser Antilles. Many of the Caribbean blindsnakes in these three genera are pale in color, indicating that they inhabit sandier soils than species found in the dark soils of mainland rainforests. Eight Cubatyphlops and four Typhlops taxa have been described in recent years, suggesting there are a great many species awaiting recognition.

TTL 4 in (100 mm) Yonenga Blindsnake (Amerotyphlops yonengae) to 20½ in (522 mm) Reticulate Blindsnake (A. reticulatus)

SCOLECOPHIDIA—Superfamily Typhlopoidea

reproduction

diet

Ant and termite eggs and larvae, soft-bodied invertebrates

The fourth genus, Amerotyphlops (15 species), is primarily found on the Latin American mainland, from southern Mexico to northern Argentina, with six species recorded for Brazil, four of them endemic. Not all Amerotyphlops are mainland species, the most widely distributed South American species, the South American Striped Blindsnake (A. brongersmai) being also found on Trinidad together with the endemic Trinidad Blindsnake (A. trinitatus), which also inhabits Tobago. There is also an endemic species in the southern Lesser Antilles, the Grenada Bank Blindsnake (A. tasymicris). One of the most distinctive members of genus Amerotyphlops is the relatively stout Reticulated Blindsnake (A. reticulatus). It is dark brown or black dorsally and immaculate white ventrally, with a stark line of demarcation midway up the flank, like a ship’s Plimsoll line, and a white snout and tail tip. This is a common species across northern South America and immediately distinguishable by girth, pattern, and size (up to 15¾ in/400 mm) from the slender leptotyphlopids with which it occurs in sympatry.

| The Reticulate Blindsnake (Amerotyphlops reticulatus) is a widespread and large Amazonian species with a distinctive two-tone body and white head and tail. top

| The Yucatan Blindsnake (Amerotyphlops microstomus) is a small endemic Yucatan species that is preyed upon by coralsnakes (Micrurus spp.). above

81

GERRHOPILIDAE

GLANDULAR BLINDSNAKES

T | The Sri Lankan Blindsnake (Gerrhopilus ceylonicus) is one of two gerrhopilid blindsnakes known from that diverse island nation. below

distribution

habitats

activity

India, Sri Lanka, Thailand, Philippines, Java, Moluccas, Papua New Guinea, and possibly Mauritius

Rainforest, woodland, and islands

Fossorial, semi-arboreal

size

Oviparous, clutch sizes unknown

genera

Cathetorhinus and Gerrhopilus

82

he family Gerrhopilidae was erected from within the Typhlopidae in 2010 because the molecular clock demonstrated that it diverged from the Typhlopidae during the Early Cretaceous (110 mya), having evolved on an eastern Gondwanan landmass, comprising India and Madagascar, known as Indigascar. Gerrhopilids exhibit small glands of unknown purpose on their head scales. The genus Gerrhopilus (22 species) is recorded from India, Sri Lanka, the Andaman Islands, Thailand, the Philippines, Indonesia, and Papua New Guinea. The latter country has nine species, the most distinctive being the pale violet Normanby Island Beaked Blindsnake (G. persephone), whose holotype was found climbing a rainforest tree trunk, possibly following the trail of arboreal termites. One monotypic gerrhopilid genus presents an enigma. Cathetorhinus melanocephalus was described in 1844 from its small (7 in/183 mm) holotype. Its origin is unknown, with Timor, Australia, Mauritius, and Tenerife all proposed, but Mauritius the most likely location.

TTL 5 in (130 mm) Jan’s Wormsnake (Gerrhopilus mirus) to 13 in (328 mm) Lowland Beaked Blindsnake (G. depressiceps)

SCOLECOPHIDIA—Superfamily Typhlopoidea

reproduction

diet

Presumed soft-bodied invertebrates such as termites

XENOTYPHLOPIDAE

MALAGASY BLINDSNAKES

L

ike the Gerrhopilidae, the Xenotyphlopidae was erected in 2010 for a single Malagasy endemic blindsnake that had diverged from the main typhlopid lineage in the Late Cretaceous (90 mya), probably on the Indigascar landmass. Grandidier’s Blindsnake (Xenotyphlops grandidieri) is found in the extreme north of Madagascar, under large stones in dry coastal forest and arid, scrubby sand dunes. It is an extremely distinctive blindsnake, pale pinkish-gray with a blunt head covered by a large, flat rostral scale. The eyes are absent; this truly is a blind snake. The limited range of this species makes it vulnerable, especially as the area is being deforested

for the charcoal industry and is also mined. The IUCN lists Grandidier’s Blindsnake as Critically Endangered. Some authors recognize a second species, Mocquard’s Blindsnake (X. mocquardi). Nothing is known of the natural history of this blindsnake but it can be presumed to be similar to that of the typhlopoids.

| Grandidier’s Blindsnake (Xenotyphlops grandidieri) is confined to northern Madagascar, where it is deemed Critically Endangered by the IUCN. There are no eyes on the head of this snake, it truly is a blind snake. below

distribution

activity

Northern Madagascar

Fossorial

genera

reproduction

Xenotyphlops habitats

Presumed oviparous, clutch size unknown

Sandy forest and coastal scrub

diet

size

TTL 5 in (130 mm) Grandidier’s Malagasy Blindsnake (Xenotyphlops grandidieri)

Presumed soft-bodied invertebrates

83

ALETHINOPHIDIA: CLADE AMEROPHIDIA The etymology of Alethinophidia is alethin = real or true, -ophidia = snakes. All extant snakes, except the aforementioned scolecophidians, are placed in the Alethinophidia. While there are small alethinophidians with tiny mouths, which feed on soft-bodied invertebrates, the greater majority are referred to as macrostomatans (big mouths) because they have evolved adaptations of the skull, jaws, and connective tissue that enable them to swallow animals wider than their own heads. The great divergence in the Alethinophidia occurred in the Mid-Cretaceous (116–97 mya) during the breakup of West Gondwana into modern-day Africa and South America. The two alethinophidian clades arising at this time were the Afrophidia and the Amerophidia. The Amerophidia evolved in the portion of West Gondwana that became South America, but they never spread out from there; modern amerophidians are still confined to tropical America. The Amerophidia is represented by a single superfamily, the Anilioidea, which contains just two families, three genera, and 36 species. There is a small-mouthed fossorial species, which resembles the afrophidian pipesnakes (Cylindrophis spp.), and relatively large-mouthed macrostomatan constrictors, which can be considered convergent with some of the smaller afrophidian boas and pythons, but amerophidians never evolved venom delivery systems like more advanced afrophidians. The two amerophidian families are very different in their physical appearance, behavior, and ecology, but they are linked together by the fact that their ancestral histories cannot be traced back to Africa.

| The Northern Eyelash Boa (Trachyboa boulengeri) is a small secretive amerophidian from Panama, Colombia, and Ecuador. left

ANILIIDAE

SOUTH AMERICAN PIPESNAKE | The South American Pipesnake (Anilius scytale) is a secretive species that lives in rainforest leaf litter and feeds on other elongate vertebrates. below

T

he family Aniliidae comprises a single species, the South American Pipesnake (Anilius scytale), which resembles the South Asian pipesnakes (Cylindrophis) more than other amerophidians. It has a cylindrical body, a rounded head, small eyes, a smooth-scaled body, and a short tail. It can achieve 3 ft 3 in (1 m) in length, and it is distinctively patterned red above, cream below, with black rings encircling the body. It is a semi-fossorial species, which burrows in rainforest leaf litter and is nocturnal to crepuscular in its activity. It is a PanAmazonian lowland species that also inhabits gardens and plantations. Prey comprises small snakes, amphisbaenians, caecilians, and elongate lizards and fish. In defense it rolls into a ball and raises its stumpy tail as a pseudohead, either to invite attacks to that less vulnerable part of its body, or to intimidate its enemy. The South American Pipesnake is viviparous, females producing litters of up to 15 neonates.

distribution

size

reproduction

Amazonian South America and Trinidad

Viviparous, litters of 5–15 neonates

genera

TTL 3 ft 3 in (1 m) South American Pipesnake (Anilius scytale)

Anilius

activity

Small snakes, amphisbaenians, caecilians, eels

habitats

Semi-fossorial

Rainforest and cultivated habitats

86

ALETHINOPHIDIA—Clade Amerophidia

diet

TROPIDOPHIIDAE

WOODSNAKES, TROPES, DWARF BOAS, AND EYELASH BOAS

T | The Northern Eyelash Boa (Trachyboa boulengeri) is so called because it possesses small fleshy supraciliary projections over its eyes. below

ropidophiidae comprises two genera and 35 species. The smaller of the genera is Trachyboa, the rough-scaled eyelash boas, so-called because of fleshy protuberances over the eyes. The Northern Eyelash Boa (Trachyboa boulengeri) occurs from Panama to Ecuador, and the Southern Eyelash Boa (T. gularis) inhabits the Pacific coast of Ecuador. Eyelash boas are viviparous with litters of one to six neonates. When threatened they freeze and, being small and well camouflaged, this makes them invisible in the leaf litter. Their prey preferences in nature are unknown, but in captivity they accept fish and small mice. Tropidophis is the larger genus in the Tropidophiidae, with 33 species, five occurring on the South America mainland. Although these snakes are often called dwarf boas they are amerophidians and, therefore, not true boas. Three species inhabit the Brazilian Atlantic coastal forests.

distribution

habitats

activity

Greater Antilles, Bahamas, Pacific coastal and Andean Panama, Colombia, Ecuador, and Peru, and Atlantic coastal Brazil

Xerophilic or mesophilic, rainforest, dry forest, coastal scrub, and islands

Nocturnal, terrestrial to low arboreal, often under debris or stones

size

reproduction

TTL 13 in (321 mm) Taczanowsky’s Dwarf Boa (Tropidophis taczanowskyi) to 3 ft 6 in (1.06 m) Black-tailed Woodsnake (T. melanurus)

Viviparous, litters of 2–8 neonates

genera

Trachyboa and Tropidophis

diet

Small lizards and frogs

87

| The Southeastern Brazilian Dwarf Boa (Tropidophis paucisquamis) is one of only five mainland South American Tropidophis. It is found far from the main distribution of the genus which is centered on the Greater Antilles. right

| The Black-tailed Woodsnake (Tropidophis melanurus) is the largest member of its genus but only one of 17 species of woodsnakes found on the island of Cuba. left

The Brazilian Dwarf Boa (Tropidophis paucisquamis) and Bahia Dwarf Boa (T. grapiuna) are found in forests, whereas the Minais Gerais Dwarf Boa (T. preciosus) is found in rocky meadows between forest blocks. All three Atlantic forest species are found in cool habitats at elevations of 1,600– 4,100 ft (500–1,250  m), while Taczanoweksy’s Dwarf Boa (T. taczanowskyi) inhabits the Peruvian Andes. The precise type locality of Battersby’s Dwarf Boa (T. battersbyi) is unknown. Body scales range from smooth in T. battersbyi to strongly keeled in T. taczanowskyi and T. grapiuna. The South American species are nocturnal, viviparous, and prey on frogs and lizards. The remaining 28 Tropidophis species are Caribbean, where they are referred to as woodsnakes. Cuba has 17 species; Jamaica, three; the Cayman Islands, two; and the Bahamas, two. One species is recorded from each of Hispaniola, Turks and Caicos, and Navassa, although the Navassa Woodsnake (T. bucculentus) is believed to be extinct. The IUCN lists four species of Tropidophis

as Critically Endangered, four as Endangered, two as Vulnerable, and two as Near Threatened. The most widely distributed and largest Cuban species is the Cuban Black-tailed Woodsnake (T. melanurus), which is found in most habitats. It can capture, constrict, and swallow small vertebrates ranging from frogs and lizards to rodents and birds. When threatened it rolls into a defensive ball while secreting a noxious white fluid from its cloacal glands, or it will autohaemorrhage from its mouth and eyes, presumably suggesting to a predator that it is long dead and bad to eat. One of the most vulnerable species is the declining Portland Ridge Woodsnake (T. stullae), which is endemic to Portland Point, southern Jamaica and listed as Critically Endangered. All woodsnakes are viviparous, T. melanurus producing up to 36 neonates. They are terrestrial and semi-arboreal predators of small vertebrates, but, being small constrictors, they are completely harmless to humans.

89

ALETHINOPHIDIA: CLADE AFROPHIDIA: CLADE HENOPHIDIA All remaining alethinophidian snakes belong in the Afrophidia, the “Out of Africa” clade, whose ancestors evolved in that part of West Gondwana that became Africa. The Afrophidia comprises two clades, the Henophidia (heno = old, ophidia = snakes) and the Caenophidia. The Henophidia contains three superfamilies, and two families which are incertae sedis. The most basal of the three is the small-mouthed Uropeltoidea, an entirely Asian clade containing three families: the Anomochilidae (dwarf pipesnakes), Cylindrophiidae (Asian pipesnakes), and Uropeltidae (shieldtails and earthsnakes). The other two superfamilies contain the largest snakes in the world, impressive macrostomatan (big-mouthed) snakes capable of swallowing large vertebrates whole. Pythonoidea is an Eastern Hemisphere superfamily containing the African-Asian-Australasian Pythonidae (pythons) and Southeast Asian Xenopeltidae (sunbeam snakes), but also the monotypic American Loxocemidae (Mexican Burrowing Python). The Booidea contains most of the snakes once called “boas” (excluding Tropidophiidae). It comprises seven families: the Boidae (“true boas”), Charinidae (North American dwarf boas), and Ungaliophiidae (Central American dwarf boas); the Erycidae (sand and ground boas) from Africa, Asia, and southeastern Europe; the monotypic West African Calabariidae (Calabar Ground Boa), the Sanziniidae (Malagasy boas), and Candoiidae (Pacific boas). The Booidae is absent from python-rich Australia. Two incertae sedis families are the Bolyeriidae (Round Island boas) from Mauritius and Xenophidiidae (spine-jawed snakes) from Southeast Asia. | The juvenile Amazonian Emerald Treeboa (Corallus batesii) will go through an ontogenetic color change to green between 18 and 24 months of age. left

ANOMOCHILIDAE

DWARF PIPESNAKES

A

lso known as the lesser pipesnakes, the Anomochilidae contains a single genus, Anomochilus (three species) from Southeast Asia. Rarely encountered and poorly studied, they rarely achieve 15¾ in (400 mm) in length, but may represent an important transitional group. Leonard’s Dwarf Pipesnake (A. leonardi) is known from West Malaysia and Sabah (Malaysian Borneo); Weber’s Dwarf Pipesnake (A. weberi) is found in Sumatra and Kalimantan (Indonesian Borneo); and the Mount Kinabalu Dwarf Pipesnake (A. monticola) inhabits Mount Kinabalu, Sabah. A total of 12 specimens are known. Dwarf pipesnakes inhabit the leaf litter of lowland and montane rainforest from an elevation of 65 ft (20 m) to over 5,000 ft (1,500 m) and are often associated with rainforest creeks. They are cylindrical snakes with rounded heads and short tails. Dorsally, they are fairly unicolor but white or yellow blotches are often present on the underside and snout, and an orange or red ring may encircle the short tail. Although the three Anomochilus are generally

| Leonard’s Dwarf Pipesnake (Anomochilus leonardi) is known from the Malaysian Borneo state of Sabah and also the Malaysian Peninsula. There is much still to be learned about these poorly studied snakes and probably more species to be discovered. opposite

| The Mount Kinabalu Dwarf Pipesnake (Anomochilus monticola) is the largest known member of the genus, from Sabah state, Malaysian Borneo. below

distribution

size

Malaysia, Peninsular and Sabah (Borneo); Indonesia, Sumatra and Kalimantan (Borneo) genus

TTL 9 in (230 mm) Sumatran Dwarf Pipesnake (Anomochilus weberi) to 20½ in (521 mm) Mount Kinabalu Dwarf Pipesnake (A. monticola)

Anomochilus

activity

habitats

Lowland and highland rainforest, often near streams

92

ALETHINOPHIDIA—Clade Afrophidia: Clade Henophidia

Nocturnal, semi-fossorial in wet leaf litter

thought to be fossorial in habit, they lack any reinforcement to their snouts for burrowing, as seen in the scolecophidians, Asian pipesnakes (Cylindrophiidae), and shieldtails and earthsnakes (Uropeltidae). Nothing is known about the dietary preferences of these small snakes, but the small gape of the mouth, the shortness of the quadrate bone that

reproduction

Oviparous, clutches of up to 4 eggs diet

Presumed elongate soft-bodied invertebrates, possibly slender vertebrates (small snakes, legless lizards)

in other snakes makes lower jaw articulation possible, and the lack of a mental groove down the throat, suggests they feed on earthworms or slender elongate vertebrates. The arrangement of the anomochilid dentition is unlike that of any other snake in that their pterygoid and palatine bones are toothless and they possess just four obliquely orientated teeth on the maxillary bone. They demonstrate elements of both typhlopid and cylindrophid dentition and may represent a transitional clade between the Scolecophidia and the Alethinophidia. The dwarf pipesnakes appear to differ from other members of the Uropeltoidea by being oviparous, the basal reproductive strategy for squamate reptiles.

93

CYLINDROPHIIDAE

ASIAN PIPESNAKES

T

| The Common Pipesnake (Cylindrophis ruffus) is found in Malaysia, Singapore, and the Greater Sunda Islands (Borneo, Sumatra, and Java).

he Cylindrophiidae contains a single genus, Cylindrophis, and 15 species of semi-fossorial, cylindrical snakes, with smooth scalation, and vestigial hind limbs as small claws either side of the cloaca. Pipesnakes are found in pristine and human-altered habitats, often close to water, and they prey on elongate vertebrates, such as lizards, snakes, or eels. They are viviparous, producing

opposite

| Blanford’s Pipesnake (Cylindrophis lineatus) is one of the more spectacularly patterned members of the genus. It is one of three species found in Sarawak state, Malaysian Borneo. below

distribution

size

Southern China, Hainan, Myanmar, Thailand, Laos, Vietnam, Cambodia, Malaysia, Indonesia, Timor-Leste, also Sri Lanka

TTL 12 in (300 mm) Damar Pipesnake (Cylindrophis aruensis) to 3 ft 3 in (1 m) Common Pipesnake (C. ruffus)

genus

Nocturnal, semi-fossorial in wet leaf litter

Cylindrophis habitats

Lowland rainforest

activity

reproduction

Viviparous, litters of up to 15 neonates diet

Caecilians, amphisbaenians, snakes, eels

94

ALETHINOPHIDIA—Clade Afrophidia: Clade Henophidia

litters of 1–15 neonates. Their defense involves hiding the head within the coils and raising the brightly patterned tail as a pseudohead. Cylindrophis is primarily Southeast Asian, with one species entering southern China, while the endemic Sri Lankan Pipesnake (C. maculatus) is the sister taxon to the rest of the genus. The most widely distributed species was the Common Pipesnake (C. ruffus), when it served as a catch-all species into which all specimens that could not be immediately identified were placed. Molecular taxonomy and a resurgence of interest in the genus have resulted in C. ruffus being confined to Malaysia, Singapore, Borneo, Sumatra, and Java. Its former mainland populations are now treated as separate species: the Burmese Pipesnake (C. burmanus) and Slowinski’s Pipesnake (C. slowinskii) in Myanmar, and the Indo-Chinese Pipesnake (C. jodiae) in the rest of Southeast Asia and southern China.

Apart from C. ruffus, Borneo is also home to the endemic Striped Pipesnake (C. lineatus) and rare Engkari Pipesnake (C. engkariensis), while Java is home to a second species, the Suboculate Pipesnake (C. subocularis), which has a subocular scale under each eye. Endemic island or island-group species inhabit Sulawesi; Jampea Island, south of Sulawesi; Boano Island, west of Seram; the Lesser Sunda Islands; Timor and Wetar; and the Tanimbar Islands. Some species, like the Common Pipesnake, are frequently encountered, especially after rain, but other species are extremely poorly documented, four species being known from only one to four specimens. Four of the 15 pipesnake species have been described since 2015. Doubtless, further new species await discovery. The Boano Island Pipesnake (C. osheai) was described in 2018, and named after this author.

95

UROPELTIDAE

SHIELDTAILS AND EARTHSNAKES

T

| Trevelyan’s Shieldtail (Rhinophis homolepis) is a Sri Lanka shieldtail with a narrow pointed head and a bulbous tail.

he Uropeltidae is an endemic South Asian family containing 61 species in seven genera. The genera Melanophidium, Plecturus, Pseudoplecturus, Teretrurus, and Uropeltis are endemic to southern India, while Platyplecturus and Rhinophis are represented in both India and Sri Lanka. India has 42 endemic uropeltids and Sri Lanka has 18, with one species, the Madura Shieldtail (Platyplecturus madurensis), occurring in both countries, but represented by different subspecies.

opposite

| The Mahableshwar Shieldtail (Uropeltis macrolepis) is a relatively large Indian member of the Uropeltidae, which exhibits the strange tail that earns the shieldtails their name. below

distribution

Sri Lanka and southern India genera

Melanophidium, Platyplecturus, Plecturus, Pseudoplecturus, Rhinophis, Teretrurus, and Uropeltis

activity

habitats

reproduction

Rainforest and agricultural habitats, i.e., plantations, gardens, dairy fields

Viviparous, litters of 2–6 neonates

size

Earthworms and soft-bodied invertebrates

TTL 7 in (180 mm) Travancore

96

Shieldtail (Rhinophis travancoricus) to 29 in (740 mm) Large-scaled Shieldtail (Uropeltis macrorhyncha)

ALETHINOPHIDIA—Clade Afrophidia: Clade Henophidia

Nocturnal, fossorial or semi-fossorial under stones, cowpats, or horse manure

diet

They are curious snakes, possessing cylindrical bodies covered in shiny, close-fitting scales, their heads are often pointed, and they have tiny eyes; but it is the tails of some uropeltids that make them distinctive. Some species have tails that taper gradually, with a pair of terminal nubbins, for example, the Nilgiri Earthsnake (Plecturus perrotetii), but many uropeltids have tails that terminate suddenly, either as a rounded scar-like stump, such as Trevelyan’s Shieldtail (Rhinophis homolepis), or in an oblique line that looks as if it has been cut through with a knife, as in the Large-scaled Shieldtail (Uropeltis macrolepis). As burrowing snakes, it is possible that the truncated tail collects soil to serve as a protective “back-door” in the burrows they make. Another adaptation of the uropeltids is the way in which they burrow. The shieldtail draws its

backbone forward in a series of S-bends, like an accordion, to provide the anchorage against the tunnel walls that enables the snake to drive its pointed head forward through the soil. It then draws its backbone and body forward again, to widen the tunnel and provide an anchorage for the next push forward. Shieldtails and earthsnakes occur in lowland and montane habitats up to 6,500 ft (2,000 m), in habitats ranging from pristine rainforest to agricultural fields, and can be very common where they occur. They appear to feed almost exclusively on earthworms and may congregate under fresh cowpats or horse manure. All uropeltids are viviparous, producing small litters of neonates.

97

BOLYERIIDAE

ROUND ISLAND BOAS

R

ound Island is a tiny (0.6 sq miles/1.59 sq km) uninhabited island 14 miles (22.5 km) north of Mauritius, in the Indian Ocean. Since 1957 it has been the subject of an intensive conservation program to recover and protect its flora and fauna. There were two endemic boa species— technically known as “split-jaw snakes” because of the primitive division of the maxillary bones into hinged anterior and posterior halves. They also lack the cloacal spurs of true boas. The recovery program came too late for the Round Island Burrowing Boa

(Bolyeria multocarinata), which has not been seen since 1975 and is listed as Extinct by the IUCN. The future of the Round Island Keel-scaled Boa (Casarea dussumieri) is brighter. From only 250 adult snakes, a captive breeding program by the Mauritius Government and Jersey Wildlife Conservation Trust has increased numbers to over one thousand adults. It is a small species that feeds on lizards and lays up to 11 eggs. The hatchlings are bright orange, becoming gray as they mature. This change is known as an ontogenetic color change.

| Saved in the nick of time, the Round Island Boa (Casarea dussumieri) was saved by an intensive captive breeding program and stringent conservation efforts on its native island. left

| The Malaysian Spine-jawed Snake (Xenodon schaeferi) is a rare leaf litter-dwelling species from the Malaysian Peninsula that probably feeds on soft-bodied invertebrates. right

Round Island, Mauritius

Island Keel-scaled Boa (Casarea dussumieri)

genera

activity

Bolyeria (extinct) and Casarea

Nocturnal, fossorial or semi-fossorial

habitats

reproduction

Dry island forest

Oviparous, clutches of 3–11 eggs

size

diet

TTL 3 ft 3 in (1 m) Round Island Burrowing Boa (Bolyeria multocarinata) to 5 ft (1.5 m) Round

Lizards

distribution

98

ALETHINOPHIDIA—Clade Afrophidia: Clade Henophidia

XENOPHIDIIDAE

SPINE-JAWED SNAKES

T

he curious family Xenophidiidae is Southeast Asian. The sole genus, Xenophidion, contains the Malaysian Spine-jawed Snake (X. schaeferi) and the Borneo Spine-jawed Snake (X. acanthognathus). The common name originates from a unique palatine projection on the maxilla. They do not appear to be closely related to any other Southeast Asian snakes and exhibit granular head scalation and a pair of enlarged prefrontal scales. The Borneo Spine-jawed Snake is known from Sabah and Sarawak in Malaysian Borneo.

The Malaysian Spine-jawed Snake was first recorded from near Kuala Lumpur, but its type locality is now destroyed. It has also been recorded from elsewhere on the Malaysian Peninsula and a possible third species has been found on Sumatra. Little is known about the natural history of these secretive snakes. They inhabit rainforest, usually near small watercourses, and appear to be terrestrial and nocturnal in habit. It is thought they feed on earthworms, insects, and possibly lizards, and they likely lay eggs.

distribution

Malaysia, Malay Peninsula, Sabah and Sarawak (Borneo), Indonesia, Sumatra genus

Xenophidion

schaeferi) to 13¼ in (337 mm) Borneo Spine-jawed Snake (X. acanthognathus) activity

Nocturnal, terrestrial or semi-fossorial reproduction

Lowland rainforest

Presumed oviparous, clutch size unknown

size

diet

TTL 10¼ in (263 mm) Malaysian Spine-jawed Snake (Xenophidion

Earthworms, soft-bodied invertebrates, small lizards

habitats

99

XENOPELTIDAE

SUNBEAM SNAKES

T

he Pythonoidea, the second superfamily of the Henophidia, contains three families, the first of these being the Xenopeltidae. The Sunbeam Snake (Xenopeltis unicolor) is common and widely distributed from Myanmar to Java and the Philippines, and achieves over 3 ft 3 in (1 m) in length. The Hainan Sunbeam Snake (X. hainanensis) is endemic to China’s Hainan island. The common name originates from the smooth, highly iridescent scales, which also provide the alternative name, “iridescent earthsnake.” The changing rainbow effect of the snake’s body may

confuse potential predators. Iridescent scales are not rare in nocturnal snakes, for example, the Rainbow Boa (Epicrates cenchria) and Amethystine Python (Simalia amethistina). Sunbeam snakes inhabit lowland rainforest, freshwater swamps, and agricultural habitats like rice-paddies. They are terrestrial or semi-fossorial, and hunt small vertebrates, such as frogs, snakes, and small mammals. Oviparous, they may produce relatively large clutches of eggs. Juvenile sunbeam snakes often exhibit a white collar, which disappears at maturity.

| The Sunbeam Snake (Xenopeltis unicolor) has an iridescent “oil on water” sheen to its scales that is clearly visible in this photograph. right

distribution

size

reproduction

Southern China, Southeast Asia, and Indonesia, also Palawan

TTL 24¾ in (628 mm) Hainan Sunbeam Snake (Xenopeltis hainanensis) to 4 ft 4 in (1.33 m) Sunbeam Snake (X. unicolor)

Oviparous, clutches of 3–17 eggs

genus

Xenopeltis habitats

Lowland rainforest, swamps, and rice-paddies

100

activity

Nocturnal, terrestrial, semi-aquatic or semi-fossorial in leaf litter

ALETHINOPHIDIA—Clade Afrophidia: Clade Henophidia

diet

Small mammals, birds, lizards, frogs, snakes

LOXOCEMIDAE

MEXICAN BURROWING PYTHON

T | The Mexican Burrowing Python (Loxocemus bicolor) is the only Western Hemisphere member of the superfamily Pythonoidea. below

he Pythonoidea is primarily an Eastern Hemisphere superfamily, so it is curious to find a “python” in the Western Hemisphere. Family Loxocemidae contains the monotypic genus Loxocemus, which is more closely related to the pythons and sunbeam snakes (Xenopeltis) than to other Neotropical snakes. The Mexican Burrowing Python (Loxocemus bicolor) occurs from central Mexico to Costa Rica, along the Pacific slope, with scattered records on the Caribbean slope. It has smooth, highly iridescent scales and a sharply pointed snout, an indication of its burrowing habits. The “bicolor” part of its name reflects its two-color state: dark, iridescent dorsum and immaculate white venter. Nocturnal and inhabiting lowland and low montane forests, it hunts terrestrial frogs, snakes, lizards, and small mammals, killing them by constriction, but it also raids the nests of iguanas and turtles. Mexican Burrowing Pythons are oviparous, producing four to 12 eggs. During the breeding season males engage in combat for the right to mate with available females.

distribution

activity

Western Mexico to Costa Rica genus

Nocturnal, terrestrial or semi-fossorial in leaf litter

Loxocemus

reproduction

habitats

Lowland and low montane deciduous forest, thorn forest size

TTL 5 ft (1.53 m) Mexican Burrowing Python (Loxocemus bicolor)

Oviparous, clutches of 4–12 eggs diet

Small mammals, lizards, frogs, reptile eggs

101

PYTHONIDAE

AFRICAN PYTHONS

T

he Pythonidae contains 11 genera and 38 species, of which four in genus Python inhabit sub-Saharan Africa. The most familiar is the Royal Python (P. regius), also known as the Ball Python due to its defensive tactic of rolling into a ball with its head in the center. Africa’s smallest python species (