The Book of Snakes: A Life-Size Guide to Six Hundred Species from Around the World

THE BOOK OF SNAKES

A LIFE-SIZE GUIDE TO SIX HUNDRED SPECIES FROM AROUND THE WORLD

MARK O’SHEA

CONTENTS

Introduction

Evolution & diversity of snakes

What is a snake?

Prey & hunting

Enemies & defense

Reproductive strategies

Snakes & humankind

The snakes

SCOLECOPHIDIA

ALETHINOPHIDIA: AMEROPHIDIA

ALETHINOPHIDIA: AFROPHIDIA: HENOPHIDIA

ALETHINOPHIDIA: AFROPHIDIA: CAENOPHIDIA

Glossary

Resources

Index of common names

Index of scientific names

Index of taxonomic groups

Acknowledgments

INTRODUCTION

Snakes—almost everybody has an opinion about them, and often those opinions are extremely polarized, with people either fearing snakes or being fascinated by them. The sinuous movements of a snake’s body, the oil-on-water effect of its iridescent scales, the hypnotic movements of its elevated head, the unblinking gaze, the continually flickering tongue, and often the serpent’s totally unexpected and unannounced appearance, are all factors that play into its ability to convey both beauty and menace in a single tongue-flick.

It is no surprise that the snake has touched so many societies throughout history and been included in countless cultural and religious stories. By shedding its skin, it may be seen as a symbol of renewal and long life, but at the same time it is the bringer of death. It is likely that since humans first walked upon the Earth, the snake has held them in its thrall, an ever-present danger in the shadows, hidden in leaf litter, reaching out from a leafy bough, or lurking beneath dappled waters.

So, why do so many people shudder at the very word snake? Obviously, one of the reasons people fear snakes is perfectly reasonable and natural—some snakes can, and do, kill humans. Worldwide, up to 125,000 lives are lost through snakebites every year. But, putting this into perspective, figures extrapolated from World Health Organization data suggest that 1.25 million people may have died in road-traffic accidents in 2015, ten times as many as were killed by snakes over a similar 12-month period.

A venomous serpent striking from a leafy bough probably epitomizes the worst nightmare for many people. Yet this Great Lakes Bushviper (Atheris nitschei) is actually a highly specialized and wonderfully adapted predator of mammals, lizards, or frogs that only uses its venom in defense when it feels truly threatened.

A hooding Egyptian Cobra (Naje haje) an iconic image, yet the purpose of the hood is to warn potential attackers that the cobra will defend itself if necessary; it is trying to avoid confrontation, not provoke it.

There are a little over 3,700 living snake species known to science. They exhibit a truly amazing diversity of shape, size, color, pattern, and natural history. In The Book of Snakes, I will introduce the reader to 600 species, almost one in six of all snakes known. For those who are unfamiliar with snakes, I aim to dispel myths and bring enlightenment and understanding about one of the most maligned groups of animals on the planet. For those who are already snake aficionados, I hope to introduce rare or elusive species that may have previously passed beneath their radar.

In selecting which 600 species to feature in The Book of Snakes, I went for diversity, including many of the familiar names, both the popular, inoffensive snakes kept as pets, and the infamous, highly venomous species that claim lives. But I also wanted to illustrate less well-known species, from remote islands, cold mountains, arid deserts, verdant rainforests, and the open oceans—snakes with unique lifestyles or diets, and each with its own interesting story to tell. Some species are so rare that we struggled to find a single photograph to represent them. And that was the one hard-and-fast rule: if no image was available or of sufficient quality to represent the species at life size, then that species did not make the book. However, thanks to the many excellent photographers who have contributed images, we lost fewer than 30 species from the original selection.

I hope that The Book of Snakes will appeal to both armchair naturalists and experienced fieldworkers alike, but particularly that it will inspire budding herpetologists of future generations to respect, study, and protect snakes.

The little girl’s expression, her hand reaching out to explore, to make contact, both suggest awe and wonderment directed toward the sinuous serpent, a Burmese Rock Python (Python bivittatus), on the other side of the glass.

EVOLUTION & DIVERSITY OF SNAKES

Snakes are elongate animals with fragile skulls and skeletons, which may become disarticulated and separated post-mortem. It is therefore no surprise that relatively few complete snake fossils are available, most comprising a few vertebrae and skull fragments.

This alligator lizard, a member of the lizard suborder Anguimorpha, out of which the Serpentes are believed to have evolved, exhibits body elongation and limbed reduction on the road toward limblessness.

THE EVOLUTION OF SNAKES

There are two contrasting schools of thought regarding the evolutionary origin of snakes. One theory proposed that they evolved from a now extinct group of large marine reptiles known as mosasaurs, which dominated the Late Cretaceous oceans. The other theory holds that snakes have a terrestrial origin and evolved from within the Anguimorpha, a suborder of lizards that today contains the slow worms, alligator lizards, monitor lizards, and the venomous Gila monster, and beaded lizards. This latter theory is the more widely accepted, but there is still support for an aquatic mosasaur origin.

The earliest snakes may have resembled this modern Boulenger’s Pipesnake (Cylindrophis boulengeri) from Southeast Asia, being small species that preyed on cylindrical prey such as soft-bodied invertebrates or slender vertebrates. The macrostomatan snakes that could feed on broader mammalian prey probably evolved later.

The earliest snakes are now thought to date from the Middle Jurassic or Early Cretaceous period, 167–140 MYA (million years ago), with fossil examples discovered in England, Portugal, and Colorado, USA. These fossil examples comprise a few vertebrae and fragments of jawbones, but they can be readily identified as snakes by their strongly recurved teeth, a common characteristic of modern and ancestral snakes. Their discovery suggests a much earlier origin for snakes than the previously accepted Late Cretaceous, 95 MYA.

Early snakes are thought to have inhabited warm, wet, well-vegetated habitats, where they existed as terrestrial, nocturnal, wide-foraging, non-constricting stealth hunters, preying on soft-bodied invertebrates and vertebrates of lesser width than their own heads. A modern comparison might be the Asian pipesnakes (Cylindrophis). The greatest explosion in snake diversity appears to have occurred following the Cretaceous–Paleogene extinction event, 66 MYA. This led to the extinction of the dinosaurs, mosasaurs, and 75 percent of all life on Earth, but it also resulted in the rise of the mammals, a potential prey source of early snakes.

Some fossil snakes display hind limbs, including Najash rionegrina, from Late Cretaceous Patagonia, which has a well-developed pelvic girdle and what are believed to have been functional hind limbs. Three Middle Cretaceous marine species—Pachyrhachis problematicus and Haasiophis terrasanctus from Palestine, and Eupodophis descouensi from Lebanon—also had hind limbs. These species are grouped in the extinct family Simoliophiidae, but body elongation and loss of limbs does not necessarily separate snakes from lizards (see "Skeleton and Limbs").

As recently as 2016, an Early Cretaceous fossil from Brazil was described as Tetrapodophis amplectus. It had an extremely elongate body and four short pentadactyl limbs, and was reported worldwide as the first four-legged snake. But this discovery proved extremely controversial, and paleontologists now believe that the fossil is a dolichosaur, an extinct marine lizard-like reptile.

Early snakes were elongate animals with vestigial hind limbs, such as this fossil (Eupodophis descouensi) from the Middle Cretaceous. Vestigial hind limbs are still present in extant boas and pythons.

THE DIVERSITY OF MODERN SNAKES

The snakes (suborder Serpentes), along with the lizards (suborder Lacertilia) and the worm-lizards (suborder Amphisbaenia), comprise the order Squamata, the scaled reptiles. The sister clade (group) of the Squamata is the Rhynchocephalia, the beaked reptiles, a once diverse and widely distributed group of lizard-like reptiles that is now confined to New Zealand, where it is represented by a sole extant species, the Tuatara (Sphenodon punctatus). The Squamata and Rhynchocephalia together form the superorder Lepidosauria, the sister clade of the Archosauria, which contains crocodilians, birds, and extinct dinosaurs and pterosaurs.

Modern snakes are divided into two infraorders, the Scolecophidia (worm snakes) and the Alethinophidia (true snakes). The Scolecophidia comprises five families of small fossorial (burrowing) snakes. Although appearing primitive among living snakes, these are actually highly derived, having specialized considerably for their subterranean existence.

The Alethinophidia is divided into the Amerophidia, a small group that has not spread beyond Latin America, and the Afrophidia, which contains the majority of the true snakes. The Afrophidia are the Out of Africa clade, because the continent appears to be the group’s evolutionary cradle, from where it radiated worldwide. The Afrophidia is further divided into the Henophidia (old snakes), which contains the boas, pythons, pipesnakes, shieldtails, and several smaller families of small-mouthed snakes, and the Caenophidia (recent snakes).

The Caenophidia is divided into two superfamilies. The Acrochordoidea today contains just three species of aquatic filesnakes (Acrochordus), but once included the now extinct Nigerophiidae and Palaeophiidae. The sister clade to the Acrochordoidea is the huge Colubroidea, with its vast and diverse array of ratsnakes, watersnakes, treesnakes, cobras, seasnakes, and vipers. This superfamily comprises 11 families and more than 3,000 species—almost 82 percent of all living snakes.

A NOTE ON CLASSIFICATION AND SCIENTIFIC NAMES

Living organisms are classified using a hierarchical system. For snakes this would be: Kingdom: Animalia; Phylum: Chordata; Class: Reptilia; Order: Squamata; Suborder: Serpentes. Within the Serpentes, snakes are grouped into Superfamilies (ending–oidea), Families (ending–idae) and Subfamilies (ending–inae). Within the families and subfamilies are the Genera that contain the Species. A species name is a binomial, it comprises two words, and it is written in italics with only the generic part receiving a large case initial letter, i.e. Natrix helvetica. Names are not necessarily Latin, but if the name comes from another language it is latinized, i.e. the Sanskrit word Naia, for the cobra genus, is latinized to Naja. A trinomial name indicates a subspecies. The name may be accompanied by the name of the describer, and the date of publication. If the name and date are contained in parentheses, this indicates that the name has changed since it was described, usually because it has been moved to another genus, i.e. the Indian Cobra, Naja naja (Linnaeus, 1758) was originally described by Linnaeus as Coluber naja.

A family tree of snakes illustrating the divergence between the burrowing Scolecophidia (worm snakes) and the Alethinophidia (true snakes); the restricted Amerophidia and the much more successful Afrophidia; and the relatively primitive Henophidia (old snakes) and the more advanced Caenophidia (recent snakes). The Caenophidia is divided into the Acrochordoidea, and the diverse and widely distributed Colubroidea, which contains over 3,000 of the more than 3,700 living snake species. Thirty-three snake families are presented, 8 of which contain between 2 and 7 subfamilies, indicated by the vertical brown bars. Representatives from every family and subfamily are included in this book. This is a simplified family tree, the lengths of the arms are not intended to indicate the timelines since divergence between the various families or clades. Due to the constraints of space in the Acrochordoidea, entirely extinct snake families, such as the Nigerophiidae and Palaeophiidae, are omitted.

WHAT IS A SNAKE?

All amphibians, reptiles, birds, and mammals are pentadactyl tetrapods—vertebrates with four limbs, each with five digits. Snakes, as reptiles, are also pentadactyl tetrapods because their lizard ancestors were fully limbed.

The skull of a Green Anaconda (Eunectes murinus) exhibiting the highly flexible bones of the skull, the three bones of the lower jaw (quadrate, compound, and dentary), and six rows of recurved teeth, which are typical of snakes and located on the maxillae and pterygoid-palatine (inner) bones of the upper jaw, and dentary bones of the lower jaw.

SKELETON AND LIMBS

The snake skeleton comprises a skull and a spinal column. Because snakes possess extremely elongate, flexible bodies, they may have up to 500 vertebrae, although 120–240 is more common. Each vertebra is attached to a pair of ribs, which in the absence of a sternum are independent, being interconnected only by powerful intercostal muscles that enable the many modes of snake locomotion. The lack of a sternum allows the rib cage to expand outward so that the body can accommodate large meals, egg clutches, or litters of neonates. The outward expansion and mobility of the ribs is obvious in the dorsoventral flattening of a basking viper, the hooding of a cobra, and the lateral body compression of a swimming seasnake.

All snakes lack front limbs, but the vestiges of the pelvic girdle and hind limbs are present in the boas, pythons, and some other primitive snake groups. Externally, they are represented by a pair of curved horny spurs on either side of the cloaca (genital-excretory opening). Spurs are largest in males, which use them to court the female during copulation.

SKULLS AND TEETH

Unlike the skulls of mammals, turtles, or crocodilians, those of snakes exhibit kinesis, meaning that they are hugely flexible, and the individual bones are capable of the articulation required to manipulate and swallow prey. The large gape of a snake’s mouth is achieved because the lower jaw comprises six separate, flexible bones. The tooth-bearing dentary bone is attached to a toothless compound bone, which in turn is attached to the skull via an elongate quadrate bone. This arrangement permits considerable mobility in all planes, further enhanced by the fact that the left and right dentary bones are not fused at the chin. Many snakes can expand their lower jaws extremely widely to accommodate large meals, and advance each side of the lower jaw independently as the prey is swallowed.

Most snakes have six rows of recurved solid teeth, arranged on the dentary bones of the lower jaw, and both the maxilla (outer) and pterygoid-palatine (inner) bones of the upper jaw. A few snakes lack teeth from some bones—for example, the blindsnakes (Typhlopidae) lack teeth from the dentary bones, the threadsnakes (Leptotyphlopidae) lack teeth from the maxillae, and African egg-eating snakes (Dasypeltis) possess only a few teeth on the rear of the dentary and maxilla. The homologous nature of solid, ungrooved snake teeth makes it easy to distinguish snake fossils from those of lizards, which exhibit greater diversity of tooth type and shape.

INTERNAL ORGANS

Snakes have the same internal organs as other vertebrates, but due to the elongation of their bodies they are arranged less symmetrically. Of two lungs, usually only the right lung is functional and it may run for a third the length of the body, while the left lung is small and vestigial. There are two elongate kidneys, also arranged asymmetrically, a liver, a pancreas, a gall bladder, and a heart that varies in its location depending on the snake’s lifestyle—for example, whether a diving seasnake or climbing treesnake. The heart has three chambers, comprising two auricles and a ventricle, unlike the four chambers of mammalian and crocodilian hearts. The digestive system comprises an esophagus, a stomach, and small and large intestines. The sexual organs of a female consist of a pair of elongate ovaries, while males have a pair of testes and a paired hemipenis. This vulnerable organ is inverted inside the base of the tail until it is required.

VENOM-DELIVERY MECHANISMS & FANGS

Venomous snakes have specialized venom-delivering mechanisms that culminate in their fangs. The most primitive are rear-fanged snakes, with enlarged, grooved teeth on the rear of the maxillae, down which venom trickles into a bite wound. In members of the venomous Elapidae and Viperidae families, the fangs are located on the front of the maxillae. In elapids, they are fixed in position, although the kinesis of the skull allows considerable movement. The vipers have short, toothless maxillae, to which are attached extremely long fangs that are hinged so that they can swing back horizontal to the skull when not in use. When a viper strikes, the flexibility of the skull and maxillae enables the fangs to swing forward like sabers, the highly kinetic skull absorbing the shock of the strike.

SENSE ORGANS

Snakes are highly sensory animals whose sense organs differ from those of mammals. They lack an external ear or a tympanum, but they do possess a highly developed inner ear, with which they detect vibrations picked up by the columella bone, attached to the quadrate bone of the jaw. Snakes are not technically deaf; they just hear in a different way to other terrestrial vertebrates.

The snake’s eyesight is also misunderstood. The retina of a vertebrate eye contains visual cells: rods, for night vision; and cones, for color vision and visual acuity. Fossorial blindsnakes may have eyes that are little more than photo-sensitive cells, warning them when they are exposed to daylight, but other snakes possess more elaborate vision. The pupils of diurnal snakes are round, whereas those of nocturnal or crepuscular snakes are vertically elliptical, or catlike, providing the eye with more control over how much light reaches the retina. Many diurnal snakes also have dichromatic or trichromatic color vision.

The laterally positioned eyes of a snake provide it with 100–160-degree vision, but probably the best vision of any snake is that of the diurnal Asian treesnakes (Ahaetulla), which have horizontal keyhole-like pupils and a grooved snout, down which they can sight up their prey. This arrangement provides a 45-degree overlap in forward vision from both eyes, effectively providing binocular vision. These treesnakes also have a highly sensitive fovea centralis, a cone-heavy depression in the retina, enabling them to detect the slightest movements of a camouflaged lizard in the vegetation, and accurately judge distance to target.

In those species that spend their time underwater or buried in the sand, the eyes are often located in a more dorsolateral position, permitting vision without exposing the head. The Namib Sidewinding Adder (Bitis peringueyi) is one such sand-dweller with dorsally positioned eyes.

All snakes have a forked tongue. Located in the front of the lower jaw, this is often in continual movement, flicking in and out of the closed mouth through a small opening, the lingual fossa. Environmental molecules are transported on the tongue to a vomeronasal organ (olfactory sense organ) in the roof of the mouth, known as the Jacobson’s organ, allowing snakes to track down either a mate or prey, and find their way around their home range. But they do not need to flick their tongues in order to smell—snake nostrils are also packed with sensitive olfactory tissues.

The Asian vinesnakes (genus Ahaetulla) probably possess the best vision of any snake. They have horizontal pupils and can sight up their lizard prey down grooves on the snout, judging distance to target due to the considerable overlap in the vision from both eyes in front of the snout.

Many snakes that feed primarily on endothermic (warm-blooded) animals have evolved the ability to hunt in total darkness. Pythons, boas, and pitvipers (Crotalinae) all have thermosensory pits that detect the infrared body heat of their prey, enabling an accurate strike. In pythons and boas, there is a series of labial pits in the lip scales, whereas pitvipers have a single loreal pit on either side of the head (located between the nasal and preocular scales—see scalation diagram opposite). More rudimentary structures, known as supranasal sacs, are present on the heads of Old World vipers (Viperinae), and may also function as infrared-sensitive receptors for hunting.

There are also several less-studied sensory receptors in snakes. The tentacles of the Tentacled Snake (Erpeton tentaculum), for example, are thought to detect vibrations in water that indicate the presence of fish. Similarly, the strange spinous, tuberculate scales of filesnakes (Acrochordus) are believed to detect swimming fish in cloudy water.

SEXUAL DIMORPHISM AND DICHROMATISM

Males and females of many snake species are almost indistinguishable, but there are clues to their gender. Males generally have longer tails than females, with a moderately bulbous basal area where the hemipenes are located. Females, meanwhile, may have shorter and more tapering tails, and often longer bodies than males. Females of some species are also much larger than males—for example, female Green Anacondas (Eunectes murinus) and Reticulated Pythons (Malayopython reticulatus) may reach around 20–23 ft (6–7 m) and 20–33 ft (6–10 m), respectively, while males are only around 10–13 ft (3–4 m) and 13–16 ft (4–5 m) in length. Larger females can carry more eggs or neonates, but in some species the sizes are reversed—female King Cobras (Ophiophagus hannah) reach only around 10 ft (3 m), while the largest recorded male was reportedly over 16 ft (5 m) in length.

Some species exhibit sexual dichromatism, whereby males and females have different coloration or patterns—for example, the male Northern Adder (Vipera berus) is silver-gray with black markings, while the female is brown with dark brown markings. Sexual dimorphism (differing body shape or size) is rarer in snakes than dichromatism.

The Malagasy Leafnose Snake (Langaha madagascariensis) exhibits both sexual dimorphism and sexual dichromatism. The brown male bears a conical spike-shaped protuberance on his snout, while in the gray female this resembles a serrated spike

SCALATION

Snake scales are composed of keratin. The dorsal scales of the body are either smooth or keeled (ridged), and are usually arranged in imbricate (overlapping) rows. The ventral scales are usually broader, and also imbricate to permit locomotion on land, although many seasnakes have sacrificed their broad belly scales to enhance lateral body compression for swimming. The scales of the head are either a series of large scutes, as in most colubrids or elapids, or are reduced in size to numerous undifferentiated granular scales, as in most vipers and some pythons. The number and arrangement of a snake’s scales provide important clues for species identification.

SHEDDING

As snakes grow, they need to shed their skins. A snake approaching a slough will exhibit milky eyes as the cells break down to separate the old and new skins, and when the eyes become clear, the snake is ready to shed. It rubs its snout on rough objects to begin the process, then crawls out of the old skin as it becomes snagged on rocks and twigs. Snakes do not possess eyelids, hence their unblinking gaze, but instead they have transparent coverings over the eyes known as brilles or spectacles. These structures, which resemble contact lenses, are sloughed along with the rest of the skin, as is the skin on the forked tongue.

The dorsal scales of snakes are usually smooth (A) but many aquatic or desert dwelling snakes (especially keelbacks and vipers) have keeled (ridged) scales (B), while the scales of the filesnakes (Acrochordus) are tuberculate (C).

PREY & HUNTING

All snakes are carnivorous, but as a group they hunt a wide diversity of prey types and sizes. Some snakes are generalist feeders, with a catholic diet, while others are specialists that concentrate on one type of prey.

A Californian Kingsnake (Lampropeltis californiae) swallowing a rattlesnake—nothing fits inside a snake quite so snugly as another snake.

INVERTEBRATE PREY

The smallest living snakes, the scolecophidian threadsnakes (Leptotyphlopidae) and blindsnakes (Typhlopidae), have tiny mouths and limited dentition. They feed on small, soft-bodied prey such as ant or termite larvae and eggs, although some of the larger species (Acutotyphlops) take earthworms.

Vermivory, or feeding on worms, is a common feature of the diets of snakes across many families. Earthworms are the prey of the Asian shieldtail snakes (Uropeltidae) and spine-jawed snakes (Xenophidion), but numerous advanced snakes also feed on earthworms. There are even a few venomous snakes that eat earthworms—the Fiji Snake (Ogmodon vitianus) and Papuan worm-eating snakes (Toxicocalamus) in the Elapidae, and the Udzungwa Mountain Viper (Atheris barbouri) in the Viperidae.

Biologists refer to snakes that feed on slimy prey—earthworms, slugs, and snails—as goo-eaters. Molluscivorous snakes require specialized oral glands to neutralize the excessively sticky secretions produced by their prey, and have specially adapted jaws to enable them to extract the snails from their shells. Slugs and snails, and the snakes that eat them, are common in the tropics, with Dipsas and Sibon species found in tropical America, Duberria in Africa, and Pareas in Asia.

Specialized centipede-eaters are found in Central America (Scolecophis) and Africa (Aparallactus), while the American hooknose snakes (Ficimia and Gyalopion) prey on spiders and scorpions in addition to centipedes.

The Crab-eating Mangrove Snake (Fordonia leucobalia) and Gerard’s Watersnake (Gerarda prevostiana), both found in Southeast Asia, feed on freshly molted crabs and mud lobsters. And in North America, crayfish snakes (Liodytes) have specially adapted skulls to enable them to feed on hard-shelled crayfish.

PISCINE (FISH) PREY

Fish feature in the diets of many snakes, especially the freshwater aquatic keelbacks and watersnakes (Natricidae), which hunt by sight and touch. The tuberculate skin of the Indo-Australian filesnakes (Acrochordus) enables them to grasp a slimy fish while they maneuver prey into the mouth, while the Tentacled Snake (Erpeton tentaculatum) detects fish using the curious tentacles on its head. Venomous freshwater piscivorous snakes include the Aquatic Coralsnake (Micrurus surinamensis) in Amazonia, the Banded Water Cobra (Naja annulata) in Africa, and the Cottonmouth (Agkistrodon piscivorus) in the USA. Seasnakes prey on a variety of gobies, moray eels, catfish, and pufferfish, while sea kraits (Laticauda) specialize in eels. A few seasnakes eat only fish eggs—the Mosaic Seasnake (Aipysurus mosaicus) takes the eggs of benthic gobies in their seabed burrows, while the Southern Turtle-headed Seasnake (Emydocephalus annulatus) uses its enlarged lateral lip scales to scrape the eggs of blennies and gobies from coral.

AMPHIBIAN PREY

Frogs and toads, including their tadpoles, also feature in the diets of many snakes—for example, the Western Grass Snake (Natrix helvetica), Mexican Hognose Snake (Heterodon kennerlyi), and Rinkhals (Hemachatus haemachatus). Cat-eyed snakes (Leptodeira) specialize in treefrog eggs laid on leaves. Salamanders and newts are eaten by gartersnakes (Thamnophis), while salamanders are the prey of the rare Oaxacan Dwarf Boa (Exiliboa placata). Rainbow snakes (Farancia) also prey on salamanders, including the fully aquatic sirens and amphiumas, while the South American Pipesnake (Anilius scytale) and the South American Coralsnake (Micrurus lemniscatus) eat caecilians. The Tiger Keelback (Rhabdophis tigrinus) even sequesters the powerful bufotoxins from its toad prey in its own skin, rendering it both venomous and poisonous.

REPTILIAN PREY

Many desert and grassland snakes—including sandsnakes (Psammophis), skaapstekers (Psammophylax), and small terrestrial vipers (Bitis, Cerastes, and Echis)—feed on lizards. The slender, rear-fanged vinesnakes of tropical America (Oxybelis), the Caribbean (Uromacer), Africa (Thelotornis), Madagascar (Langaha), and Asia (Ahaetulla) hunt agile, alert, camouflaged lizards by stealth. The Boomslang (Dispholidus typus) takes chameleons, and the Australian Black-headed Python (Aspidites melanocephalus) preys on agamid dragons and goannas. Amphisbaenians (worm-lizards) are preyed upon by fossorial and semi-fossorial snakes, such the Small-scaled Dawn Blindsnake (Typhlophis squamosus).

Some snakes also eat other snakes. This is called ophiophagy, a term that forms the basis of the generic name of the King Cobra (Ophiophagus hannah), which is capable of swallowing a Reticulated Python (Malayopython reticulatus) more than 6 ft (2 m) long. There are snake-eating snakes on most continents, including North American kingsnakes (Lampropeltis), Latin American mussuranas (e.g. Mussurana and Clelia), African filesnakes (Gonionotophis), Asian kraits (Bungarus) and coralsnakes (Calliophis), and the Australian bandy-bandys (Vermicella). Ophiophagy is not cannibalism unless a snake eats its own species, but there are plenty of examples of this behavior, too, especially within the Elapidae.

Snakes rarely prey on turtles, but there is a record of a Puff Adder (Bitis arietans) swallowing a small tortoise. Caiman are eaten by anacondas (Eunectes), while small crocodiles are taken by water pythons (Liasis). In Florida, introduced Burmese Pythons (Python bivittatus) have been documented preying on alligators.

The Iranian Spider-tailed Viper (Pseudocerastes urarachnoides) lures birds within strike range with its spider-like tail tip.

The African egg-eating snakes (Dasypeltis) specialize in feeding on small birds’ eggs, regurgitating the eggshell afterward.

AVIAN PREY

Birds are commonly included in the diets of arboreal snakes, such as the Boomslang, which will raid the pendulous nests of weaverbirds, and the Central American Puffing Snake (Phrynonax poecilnotus). One of the most unusual bird-eating snakes is the Iranian Spider-tailed Viper (Pseudocerastes urarachnoides), whose tail tip is shaped like a spider to lure birds within strike range. Other habitual bird-eaters include the Golden Lancehead (Bothrops insularis) on Ilha da Queimada Grande, Brazil, and the Santa Catalina Island Rattlesnake (Crotalus catalinensis) from the Gulf of California, Mexico. Adult Tigersnakes (Notechis scutatus) on Australia’s Mount Chappell Island gorge on muttonbird chicks once a year, while on Guam, the introduced Brown Treesnake (Boiga irregularis) has eaten most of the island’s endemic flightless bird species into extinction.

The Southern African Rock Python (Python natalensis) can constrict and devour large mammals such as this nyala calf.

MAMMALIAN PREY

Rats, mice, rabbits, and similar small mammals constitute the primary prey of numerous nonvenomous and venomous snakes. Some even specialize in hunting bats, including the Borneo and Malaysian Cave Racers (Elaphe taeniura grabowskyi and E. t. ridleyi). Ratsnakes and boas employ constriction to kill their prey, but sit-and-wait ambushers like vipers and rattlesnakes use venom. Pythons, boas, and pitvipers can locate their warm-blooded mammalian prey in total darkness using their heat-sensitive facial pits (see here).

Larger mammals, such as deer, antelope, pigs, and monkeys, may be taken by adult pythons, boas, and anacondas. The largest mammals documented as snake prey were an adult female sun bear, eaten by a large Reticulated Python, and a puma, taken by a Green Anaconda (Eunectes murinus). Humans are also occasionally killed and eaten by giant pythons (see Snakes & Humankind).

ENEMIES & DEFENSE

Snakes have many natural enemies. Small snakes may fall foul of large venomous invertebrates, but it is among other vertebrates that most snake predators are to be found. To avoid being killed and eaten, snakes have evolved an entire armory of weapons and subterfuges.

ENEMIES

Probably the most well known of all snake killers is the mongoose, famously embodied as Rikki-Tikki-Tavi in Rudyard Kipling’s Jungle Book. But these agile mammals are not confined to India; there are also mongooses throughout Southeast Asia and Africa. With their quick reactions and thick body fur, and a degree of immunity to cobra venom, mongooses are able to avoid, ward off, and even survive most snake strikes. Seen as a means of controlling snakes and rats, mongooses were introduced to Okinawa, Jamaica, Hawaii, Fiji, Mauritius, and other islands, where they have caused considerable environmental damage and extinctions. Less well known than the mongoose story is the fact that the European hedgehog will also kill and eat snakes, as will many smaller carnivores such as cats.

Among the birds, snake-eagles, fish-eagles, hornbills, and secretary birds are all snake predators. In the reptiles, crocodiles, monitor lizards, and ophiophagous snakes—especially the King Cobra (Ophiophagus hannah), American kingsnakes (Lampropeltis), and African filesnakes (Gonionotophis) —all prey on snakes. After all, nothing fits inside a snake so well as another snake! Even the most venomous snakes, the seasnakes, are commonly found in the stomachs of tiger sharks. But humankind is the snake’s worst enemy.

The large East African Gaboon Viper (Bitis gabonica) has a body patterned like a pastel-colored Persian carpet, and a head like a huge leaf. This complex cryptic patterning serves to break up its outline when it is lying in woodland leaf litter.

The venomous Eastern Coralsnake (Micrurus fulvius, top) can be distinguished from its harmless mimic, the Scarlet Milksnake (Lampropeltis elapsoides, bottom) by the order of its bands and the rhyme Red to yellow, kill a fellow, Red to black, venom lack, but this rhyme does not work in South America.

DEFENSIVE STRATEGIES

Snakes have an array of defenses to avoid detection or warn off predators. Many snakes are highly camouflaged or cryptically patterned to enable them to hide in leaf litter or vegetation. Vinesnakes (Oxybelis, Ahaetulla, and Thelotornis) really do look like vines, while the head of a Gaboon Viper (Bitis gabonica) resembles a large dead leaf, and the rest of its Persian carpet patterning serves to break up its outline for both predator and prey alike. A few nocturnal snakes, such as rainbow boas (Epicrates), have iridescent body scales that shimmer in daylight and may also break up their outline when approached by a potential predator. American coralsnakes (Micrurus and Micruroides) are brightly banded red, yellow, and black, advertising that they are dangerous and should be left alone, a pattern mimicked by some harmless snakes to avoid interference.

Some snakes go in for big visual threat displays. Examples include the cobras (Naja), with their hooding; the Boomslang (Dispholidus typus), which inflates its neck to expose the contrasting colors of its interstitial skin; and the Black Mamba (Dendroaspis polylepis), with its wide-mouth gaping, exposing the black interior. Other snakes rely on auditory warnings, such as the buzzing tail of a rattlesnake (Crotalus), the sawing sound made by a carpet or saw-scale viper (Echis) as its continual motion causes its serrated keeled dorsal scales to rub together, or the loud hissing of a Russell’s Viper (Daboia russelii), Puff Adder (Bitis arietans), or Bullsnake (Pituophis catenifer sayi).

The Cape Twigsnake (Thelotornus capensis) inflates its throat to expose the interstitial skin, making itself look larger and more threatening to potential predators.

The Zebra Spitting Cobra (Naja nigricincta, above left) spreads a hood as a warning that it is dangerous, and if that fails it will send twin jets of venom into the eyes of its perceived enemy.

The Western Diamondback Rattlesnake (Crotalus atrox,) avoids confrontations with enemies by vibrating its rattle vigorously. Every time the rattlesnake sheds its skin it adds another interlocking link to the rattle as the cross-section above illustrates. The oldest links are at the tip.

If escape is an option, then few snakes have a better method than the Paradise Flying Snake (Chrysopelea paradisi), which can flatten its entire body into a concave parachute, so that it simply glides away from the threat when it leaps from a tree. Still other snakes pretend to be something they are not, mimicking the body shape, patterning, or behavior of highly venomous coralsnakes, cobras, or vipers—the Aesculapian False Coralsnake (Erythrolamprus aesculapii), Large-eyed Mock Cobra (Pseudoxenodon macrops), and Northern False Lancehead (Xenodon rabdocephalus) all employ this defensive measure.

One of the strangest ways to avoid predation is to play dead, a behavior known as thanatosis. American hognose snakes (Heterodon), European grass snakes (Natrix), and the South African Rinkhals (Hemachatus haemachatus) all play dead when they feel threatened. The last of these also has another defense in its armory—it is a spitting cobra capable of sending jets of painful cytotoxic venom into the eyes of an enemy, effectively blinding it while the cobra makes good its escape. This is probably the only instance where a snake’s venom has evolved for defense rather than hunting.

Another very strange defense measure is cloacal popping. Some coralsnakes (Micruroides and Micrurus) and hooknose snakes (Ficimia and Gyalopion) use this technique, forcefully and noisily expelling air from their cloacas.

HUMAN THREATS AND CONSERVATION

Humans have probably persecuted snakes for centuries, either killing them out of fear or harvesting them in unsustainable numbers for their skins, their meat, or their gall bladders, an apparently essential ingredient in an eastern tonic for failing libido in men. And of course snakes suffer from the same indirect threats to their survival as other animals, habitat destruction, fragmentation, and alteration. While some snake species have slipped into extinction through the agencies and actions of man, others have been saved by the intervention of conservation bodies, captive breeding, and educational campaigns aimed at teaching villagers or islanders to not only live alongside their serpentine neighbors, but also be proud of them and protect them.

American and European zoos have been actively engaged in a captive breeding program for the endangered Aruba Island Rattlesnake (Crotalus durissus unicolor), a small, pastel-colored subspecies of the large Tropical Rattlesnake, the aim being to bolster the population in the small desert center of its island. Two extremely primitive, endemic, egg-laying, split-jaw snakes, only distantly related to any other snakes on Earth, used to live on tiny (²/3 sq miles/1.69 km²) Round Island in the Indian Ocean, until seafarers introduced goats and rabbits to the island. The invasive mammals devoured the vegetation and then the rain washed the soil into the sea, and with it went the Round Island Burrowing Boa (Bolyeria multocarinata). The other species, the Keel-scaled Boa (Casarea dussumieri) was more fortunate, it was rescued by the Jersey Wildlife Preservation Trust ( JWPT) who, working with the Government of Mauritius, have brought the species back from the brink so when the island has been restored it is hoped the species can go home. Sadly the Burrowing Boa was declared extinct by the IUCN in 1975.

The JWPT and other conservation organizations have been behind the recoveries of Caribbean snakes such as the Antiguan Racer (Alsophis antiguae), Great Bird Island Racer (A. sajdaki), and the Jamaican Boa (Chilabothrus subflavus). Snakes might not be everybody’s cup of tea but that does not mean that they do not need conservation. And conserving snakes is actually beneficial to mankind, snakes are nature’s rat catchers, eating the rodents that carry disease and devour our crops.

Snakes are rarely a vote winner when it comes to popularity, but conservation of snakes is important. Endangered species such as the Jamaican Boa (Chilabothrus subflavus) been saved from extinction by conservation organizations.

REPRODUCTIVE STRATEGIES

Unlike turtles, tortoises, crocodiles, alligators, and the tuatara, which all lay eggs, squamate reptiles employ both oviparity (egg-laying) and viviparity (live-bearing). There are advantages and disadvantages to each of these strategies.

Every spring, thousands of Red-sided Gartersnakes (Thamnophis sirtalis parietalis) emerge from communal dens in Manitoba, Canada. The males emerge first to await the females, whereupon they will compete with other males for the largest females. Some males mimic females to draw other males away and allow them to mate the females.

COURTSHIP, MATING BALLS, AND SKEINS

Sexually receptive female snakes emit pheromones, leaving a trail for males to follow with their extremely sensitive forked tongues, sometimes multiple males pursuing a single female. At the famous Manitoba snake pits, thousands of male Red-sided Gartersnakes (Thamnophis sirtalis parietalis) emerge from hibernation, only to linger around the dens to await the later emergence of the females.

Multiple male Green Anacondas (Eunectes murinus) will often court a single female, forming a mating ball around her as they jockey for position with their tails in an attempt to mate. These mating balls are usually found in shallow water, and the female may mate with several males. A similar arrangement has been observed in more active species such as the Keel-bellied Whipsnake (Dryophiops rufescens) and the Paradise Flying Snake (Chrysopelea paradisi). Here, a single female is courted as she moves through vegetation by two or three males, which form a continually writhing entanglement, known as a skein, about her body.

Green Anacondas (Eunectes murinus) may form great mating balls in the shallows or on land, one large female attracting up to a dozen smaller males, all jockeying for the best position to mate with her.

Male pythons and boas possess cloacal spurs (above right), the vestiges of their ancestral hind limbs, with which they will stroke the females during courtship.

The spurs of females are small or absent. Similarly, male Southern Turtle-headed Seasnakes (Emydocephalus annulatus) have a spike on their snouts, which they use during courtship to stroke the female’s back.

MALE COMBAT

It is quite common for two male snakes, in pursuit of the same female, to engage in combat—this behavior has been observed in adders, rattlesnakes, the King Cobra (Ophiophagus hannah), and the Black Mamba (Dendroaspis polylepis). These combats are wrestling matches that involve the competitors entwining around one another, raising up and trying to force their opponent to the ground. Combats between venomous species do not usually lead to injuries, but those between large pythons may involve spurring and result in deep wounds.

THE MECHANICS OF MATING

Snakes reproduce sexually via copulation, the male snake inserting one of his paired hemipenes into the cloaca of the female, which will lift her tail to make penetration easier. The female’s ova are fertilized internally with the male’s sperm, although this may not happen immediately—females of species that mate in the autumn are able to store sperm until more favorable conditions return in spring. Sperm is usually stored for only a few months, but much longer periods have been documented—six years in the case of the Banded Cat-eyed Snake (Leptodeira annulata).

Most tropical and subtropical snake species reproduce once a year, but in colder climates, where prey is only seasonally available and weather conditions are not ideal, the period during which a post-parturition female can recover her optimal body weight may be short. In these situations, species such as the Northern Adder (Vipera berus) in the Alps or the Carpet Python (Morelia spilota) in southern Australia may reproduce only biannually. Species in warm climates with abundant prey year-round, such as the Common Saw-scale Viper (Echis carinatus), may produce two litters each year.

A pair of male Dharman Ratsnakes (Ptyas mucosa) writhe and wrestle with one another in an attempt to win the right to mate with a nearby female. Males of many species engage in this behavior, including King Cobras (Ophiophagus hannah) and Black Mambas (Dendroaspis polylepis).

OVIPARITY OR VIVIPARITY

Birds are oviparous (egg-laying), as are turtles, crocodilians, and monotreme mammals, while all remaining mammals are viviparous (live-bearing). But this clear-cut division of reproductive strategies becomes blurred in the Squamata, especially in the snakes. Oviparity is the primitive condition for snakes, and it is the sole strategy exhibited by 15 of the 33 snake families (see here), including many of the small, fossorial, and relatively primitive snakes. Live-bearing is the only strategy found in ten snake families, primarily in the Henophidia. The remaining eight families contain both oviparous and viviparous genera, and in some cases, genera that contain both oviparous and viviparous species—for example, the viviparous Smooth Snake (Coronella austriaca) and oviparous Southern Smooth Snake (C. girondica).

A female Osage Copperhead (Agkistrodon contortrix phaeogaster) with her litter of neonates. The neonates are only days old but they will soon disperse into the surrounding undergrowth.

A female Reticulated Python (Malayopython reticulatus) with her clutch of leathery-shelled eggs. She will defend her eggs against egg thieves such as monitor lizards and incubate them by shivering thermogenesis—the continual twitching of her muscles which will elevate her body temperature by 13–23 °F (7–13 °C).

There are both advantages and disadvantages to live-bearing for snakes. Among the disadvantages is the fact that the gravid female must carry her offspring for the entire gestation period, which could be three months, during which time she is unlikely to feed, and if she is killed her entire reproductive investment is lost—she literally has all her eggs in one basket. In the tropics, it is probably advantageous for the female to lay her eggs so that she can begin hunting again, but in arctic–alpine climates live-bearing is a much better strategy. While eggs are vulnerable to cold temperatures, a live-bearing female can shelter below ground during the night or cold periods and then emerge to bask in the sun. When locomotion is combined with melanistic (black) coloration, the female snake becomes an efficient mobile incubator, seeking out the best basking spots.

Live-bearing is also a useful adaptation for aquatic snakes—the Colubrine Sea Krait (Laticauda colubrina), for example, is an oviparous marine species that must come onto land to lay its eggs, whereas viviparous true seasnakes simply give birth in the ocean and are not tied to land. Similarly, oviparous pythons must lay their eggs on land, while aquatic anacondas give birth directly into the shallow water.

EGG-LAYING

Snake eggs are oval, with opaque white leathery shells. Some snakes lay their eggs soon after mating, when embryonic development has only just begun, while other species may retain the eggs until halfway through or near the end of the incubation period. The Persian False Horned Viper (Pseudocerastes persicus) has been recorded laying eggs that hatched 30–32 days later, half the usual 60–70-day incubation period, while the Sahara Sand Viper (Cerastes vipera) lays eggs only days before they are due to hatch. Most eggs are deposited when the embryo is at the 30 percent development stage.

A hatchling Green Tree Python (Morelia viridis) uses an egg-tooth on the tip of its upper lip to pip its egg. It will breath air for the first time but may wait some time before fully emerging. At approximately 15 months of age it will take on the green adult livery.

Snakes may lay their eggs in a rocky crevice or an animal burrow, and leave them to incubate on their own. Western Grass Snakes (Natrix helvetica) often lay their eggs in garden compost heaps, sometimes communally, where the eggs benefit from heat generated by the decomposing vegetation. A few snake species remain with their eggs post-oviposition. Female pythons coil around their eggs, both to incubate and to protect them. Incubation is accomplished via a process of endogenous heat production known as shivering thermogenesis, which involves a prolonged period of rhythmic muscular contractions. Brooding Diamond Pythons (Morelia spilota) have been recorded shivering up to 50 times per minute throughout the two-month incubation period. Shivering thermogenesis will maintain an incubation temperature of 88–91 °F (31–33 °C), as much as 13–23 °F (7–13 °C) above the ambient air temperature. The pythons do not feed throughout this entire period.

A female King Cobra uses her body coils to build a nest of leaves, laying her eggs in the center. She will then remain at the nest site to protect the eggs from predators, such as the Water Monitor Lizard (Varanus salvator).

At the end of the incubation period, the young snakes hatch by making slits in the leathery shell of the egg. They use an egg-tooth on the front of the upper lip to achieve this, a process known as pipping, although they may not actually emerge for some hours. Once out of the egg, the hatchling will shed its skin and become independent. Depending on the species and the size of the female, the clutch may vary from a single egg to more than 80 in the case of large pythons.

LIVE-BEARING

Just over 20 percent of snakes are live-bearers, a process that has evolved at least 35 times within the Serpentes. Two different forms of live-bearing have been defined—viviparity and ovoviviparity—but most recent authors do not differentiate between them. Boas, rattlesnakes, most vipers, American natricid watersnakes, true seasnakes, and the Red-bellied Blacksnake (Pseudechis porphyriacus) are all viviparous. Neonates are born coiled in a transparent egg membrane that ruptures soon after birth. Litter sizes for viviparous snakes vary depending on the species and the size of the female, from one to two in small species, to more than 100 in the Puff Adder (Bitis arietans).

A female Copperhead (Agkistrodon contortrix) giving birth to a litter of neonates which are born in membraneous packages from which they almost immediately escape to take their first breaths.

VIRGIN BIRTH

Parthenogenesis is a form of reproduction whereby a female produces exact clones of herself without the need of a male. There are numerous parthenogenetic lizards, but only one truly obligate parthenogenetic snake, the Brahminy Blindsnake (Indotyphlops braminus), for which no males are known. There are also cases of females from normally bisexual species—including pythons, boas, filesnakes, gartersnakes, and pitvipers—producing offspring without first mating with a male. This is termed facultative parthenogenesis, and is the last-ditch attempt of a female to propagate when no males are available. The result is usually a small clutch or litter with a high mortality rate, and the offspring are always unisexual—all female in boas and pythons, and all male in rattlesnakes.

A two-headed Red-backed Ratsnake (Oocatochus rufodorsatus). Two-headed or dicephalic snakes are effectively conjoined twins with two heads at the same end. Although most specimens are stillborn, or die soon after birth due to other defects, there have been many cases of dicephalic snakes being raised to adulthood.

SNAKES & HUMANKIND

There are few human cultures, through history or across the world, where humans have not, or do not, live alongside snakes. Probably no other animal group has had such an effect on human culture than the snake, which has become the symbol of life and longevity, and of sudden death.

The Serpent in the Garden of Eden, tempting Adam and Eve with the apple.

SNAKES IN RELIGION

From the headdresses worn by ancient Egyptian pharaohs 3,000 years ago, to twentieth-century Appalachian snake handlers who follow the Gospel of St. Mark’s They shall take up serpents literally, snakes have exerted a powerful grip on the human psyche, representing both good and evil.

In Judeo-Christian tradition, the serpent tempted Eve to pick the apple in the Garden of Eden, and for this act God condemned it to crawl on its belly and eat dust for the rest of its days. The snake reappears in the Bible as Aaron’s rod, which swallows the rods of the Egyptian pharaoh’s wise men, and as the staff of Moses, which parts the Red Sea during the Exodus. Aaron’s rod was most likely an Egyptian Cobra (Naja haje), since cobras have an appetite for other snakes.

Cleopatra reputedly committed suicide by allowing herself to be bitten by an asp, although the serpent was probably the Egyptian Cobra again. A queen such as she would have wished for a swift and painless death, and to remain looking beautiful after her passing, and the cobra is more likely to deliver on those wishes than what we now call an asp, a viper, or a side-stabbing snake (Atractaspis).

A cobra is said to have spread its hood to shelter Buddha from the rain, and as a sign of his thanks Buddha placed a mark on the hood. For Sri Lankans, he placed two fingers and left the spectacle mark on the Indian Cobra (Naja naja), whereas for Thais he used his thumb, leaving the monoculate mark of the Thai Cobra (N. kaouthia).

The cobra sheltered Buddha from the rain by spreading its hood over his head. A grateful Buddha laid his two fingers (Naja naja) or his thumb (N. kaouthia) on the cobra’s hood and left his mark.

SNAKES IN CULTURE

Snake symbolism is everywhere. The Hopi Indians of Arizona perform a rain dance with snakes gripped in their teeth, the serpents being seen as the guardians of water. Young Venda girls in South Africa perform the domba dance during their initiation into womanhood, when they mimic the movements of a large python. In Abruzzo, Italy, an annual snake festival sees the statue of St. Domenico being paraded through Cocullo draped with dozens of harmless Aesculapian snakes (Zamenis longissimus), while visitors to the Snake Temple on the Malaysian island of Penang marvel at hundreds of venomous Wagler’s Temple Pitvipers (Tropidolaemus wagleri) lying languidly across the icons.

Snakes appear in the art of many ancient cultures, from the Rainbow Serpent cave paintings and petroglyphs of Australian Aboriginal Dreamtime, to the Feathered Serpent, or Quetzalcoatl, of pre-Columbian Mayan and Aztec societies. At the ancient temple at Polonnaruwa, Sri Lanka, there is a huge viper carved into the rocks. Also at the site is an 800-year-old stone Ayurvedic medicine boat, in which a dying snakebite victim would be placed, to be anointed with oils and herbs in the hope that he or she would survive.

Snakes feature in modern medicine, too. The Rod of Asclepius, the Greek god of healing, comprising a single Aesculapian snake curled around a staff, is used widely as the symbol for medicine. In the United States, it is sometimes exchanged for a caduceus, the symbol of the messenger god Hermes, which features two snakes coiled about a winged staff.

Today, even in our hectic commercial world, the representations of snakes are still all around us, as team mascots or in names of products as diverse as beer, candies, cement, condoms, and cars.

The Egyptian Cobra (Naja haje) is represented on the headdress of the Egyptian pharaohs.

SNAKEBITE

Around the world, between 94,000 and 125,000 people die annually from snakebites. Most snakebite victims are poor rural farmers or children in the developing world. The countries with the highest incidences of snakebite deaths include India, Sri Lanka, Nepal, Myanmar, Nigeria, Mali, Togo, Benin, Senegal, and Papua New Guinea. No data exist for Indonesia, but death rates there are also assumed to be high.

Rather than going to hospital, victims will often visit a local shaman or medicine man in the vain hope that he can save them. Even for those people who survive a snakebite, the prognosis may not be good. Some snake venoms cause massive tissue destruction, leading to limb deformity or loss—each year, up to 400,000 snakebite victims may be disabled in this way. Snakebites are terrible to endure, but they are not without a cure.

Modern antivenoms are produced from the antibodies formed when horses and sheep are injected with increasing doses of snake venom, and are very effective for saving life and reducing the damage done by snake venoms, provided the victim gets to hospital quickly. Unfortunately, however, some Western drug companies are stopping the production of antivenoms, as they are less profitable than drugs for diseases like obesity, cancer, and heart disease. The world—and Africa in particular—may consequently be entering an antivenom crisis.

SNAKE VENOMS

Snake venoms are complex cocktails of different proteinaceous toxins that are designed to target prey. With the exception of spitting cobras, which spray jets of venom into the eyes of a perceived enemy and then effect an escape, snake venoms are not purposefully defensive. There are several different venom types, which are summarized below:

Neurotoxins

These paralyze the nervous system, preventing the passage of messages along nerves and leading to death through respiratory paralysis. There are two types: presynaptic neurotoxins, which destroy the transmitter sites on the upstream side of the synaptic gap; and post-synaptic neurotoxins, which block the receptor sites on the downstream side of the gap. These venoms are primarily found in the elapids—cobras (Naja), mambas (Dendroaspis), and taipan (Oxyuranus)—but also in some rattlesnakes, including the Mohave Rattlesnake (Crotalus scutulatus).

Hemotoxins

These toxins affect the blood and circulatory system. Anticoagulants cause prolonged bleeding by preventing blood coagulation, while procoagulants do the same by using up all the clotting factor in blood. Platelet inhibitors prevent normal blood clotting, and when combined with hemorrhagins (which puncture holes in the blood vessels), the result can be massive blood loss. Hemolytic toxins break down the red blood cells, causing blockage of the kidney tubules, leading to renal failure. Many vipers produce hemotoxins, but they are also found in some elapids such as taipans.

Extracting the venom from a cobra for antivenom manufacture, a process usually called milking.

Myotoxins

These toxins affect the muscles, acting like neurotoxins by causing paralysis, or like hemotoxins by breaking down muscle tissue. They are primarily found in seasnakes.

Cytotoxins

These toxins digest protein, leading to massive tissue destruction. They are found in large vipers that need to digest bulky mammalian prey, and in the venoms of spitting cobras.

Other toxins

Sarafotoxins are cardiotoxins that cause a narrowing of the cardiac arteries; they are found in the venoms of the side-stabbing snakes (Atractaspis). The St. Lucia Lancehead (Bothrops caribbaeus) produces a cardiotoxin that causes arterial thrombosis, while the venom of the Gwardar (Pseudonaja mengdeni) contains a nephrotoxin that directly attacks the kidneys. Snake venoms are highly complex compounds.

THE SNAKES

The Scolecophidia (Scolec = worm; -ophidia = snakes) are known as wormsnakes, blindsnakes, and threadsnakes. There are over 450 species, in five families: 12.3 percent of all living snakes. They are small and slender, with highly glossed, tight-fitting scales, yet a few achieve almost 3 ft 3 in (1 m). Fossorial in habit, blindsnakes are not actually blind. Their pigmented eyespots, under translucent scales, register sunlight and warn them to burrow if exposed. Scolecophidians are highly adapted subterranean snakes.

The Anomalepididae (dawn or early blindsnakes) are South American, 18 species in four genera, the most basal of all living snakes. They possess teeth on both the maxillary and dentary bones.

The largest family, the Typhlopidae (blindsnakes), with over 270 species, inhabits the tropics and subtropics. They only