Colubrids

(Colubridae)

Class Reptilia

Order Squamata

Suborder Serpentes

Family Colubridae

Thumbnail description
Highly variable in size, body form, and color pattern; ranges from short, stout, drab species to large, slender, boldly marked forms

Size
6 in–12 ft (160 mm–3.7 m)

Number of genera, species
Approximately 300 genera; approximately 1,700 species

Habitat
The family includes terrestrial, fossorial, arboreal, and aquatic species

Conservation status
Extinct: 1 species; Critically Endangered: 6 species; Endangered: 7 species; Vulnerable: 8 species; Lower Risk/Near Threatened: 4 species; Data Deficient: 10 species

Distribution
Worldwide except Antarctica, extremely high latitudes of Eurasia and North America, and central and western Australia

Evolution and systematics

The Colubridae comprise by far the largest and most diverse family of snakes, containing about 70% of all snake species. For that reason, few useful generalizations apply to this expansive family. Indeed, it is the ability of colubrids to adapt to widely different habitats, diets, and life history modes that above all characterizes this extraordinary lineage. Although some colubrids are generalists, many exhibit strong specialization for a particular environment and/or specific prey.

Fossils attributed to the Colubridae first appear in the Lower Oligocene, about 35 million years ago. However, the group seems to have radiated rapidly during the Miocene (5–25 million years ago), and by the end of that period a fauna previously dominated by boa-like species had largely been replaced by colubrids, elapids, and viperids. However, our knowledge of fossil snake faunas is drawn primarily from temperate remains, so inferences for tropical regions should be drawn with caution.

The relationships among genera of colubrids remain poorly understood and highly controversial, despite numerous attempts to bring order to this complex group. Early classifications were based largely upon similarities in scale characteristics, dentition, and the form of the hemipenes (the paired copulatory organs of male squamates). In some cases these features yielded groupings that have stood the test of time, but in many instances the failure to distinguish between ancestral and derived conditions resulted in unnatural groups. The application of both phylogenetic systematic (cladistic) and molecular methods has helped to clarify the relationships within many groups of colubrid snakes. However, even when well-defined clusters of genera are confirmed, the relationships among those clusters often remain unclear, and widely accepted phylogenetic hypotheses concerning colubrid relationships have remained elusive. Furthermore, the relationship between colubrids and two other colubroid families, the Elapidae and Atractaspididae, is unclear, and it is possible that the Colubridae itself is paraphyletic relative to one or both of those families. That is, some colubrids may be more closely related to members of one of those families than they are to certain other colubrids.

That said, several subfamilies of Colubridae are widely recognized, if not universally accepted. Seven are recognized here. The Xenodermatinae is a small group of six genera and about 15 species from southern and eastern Asia. Little is known of the biology of these strange colubrids, many of which have unusual, protuberant scales on the body or head. Most occupy terrestrial habitats in moist tropical forests, and some are known to prey on amphibians. The Pareatinae is a small but well-defined lineage of three genera and about 18 species of Southeast Asian snakes that are highly specialized to prey on terrestrial mollusks (snails and/or slugs). A slightly larger but still well-defined lineage of Asian colubrids is the Homalopsinae, with about 10 genera and 35 species. All are strongly aquatic and some, such as the tentacled snake (Erpeton tentaculatus), rarely leave the water. Several occupy mud flats and mangrove forests, including the dog-faced watersnake

(Cerberus rynchops) and the white-bellied mangrove snake (Fordonia leucobalia), while the keel-bellied watersnake (Bitia hydroides) occupies coastal marine waters. Many feed on fishes, but some prey on frogs and Fordonia feeds on crustaceans. All are rear-fanged.

Four other subfamilies are much larger, and their monophyly is uncertain. The Natricinae is the most cohesive of these, including many species with aquatic tendencies, including the familiar North American gartersnakes (Thamnophis), North American watersnakes (Nerodia), and the grass snake (Natrix natrix) of Europe. The subfamily includes about 38 genera and almost 200 species distributed throughout Europe, Asia, Africa, and North and Central America. Especially large radiations occur in southern and eastern Asia and in North America. The American members constitute a well-defined tribe, the Thamnophiini, all of which are viviparous, in contrast to most of the Old World forms. In addition to the many aquatic species of natricines, some are small cryptozoic or fossorial forms.

Another subfamily with many northern representatives is the Colubrinae, with over 100 genera and roughly 650 species. Also included in this subfamily are many tropical species and several clusters of genera that are sometimes recognized as tribes or even subfamilies in their own right. Worldwide in distribution, the Colubrinae include significant radiations in North America, Eurasia, Africa, and Southeast Asia. Many are fast-moving terrestrial species, although arboreal and fossorial members are numerous. Many are rear-fanged, although others lack enlarged rear maxillary teeth and some have evolved constricting behavior. Among the more familiar groups are the North American racers (Coluber), kingsnakes (Lampropeltis), and ratsnakes (Elaphe). Other important members of the Colubrinae include a large group of tropical Asian burrowing snakes, including the reedsnakes (Calamaria) and related genera, and a group of African genera that include the dangerously venomous boomslang (Dispholidus) and twigsnake (Theletornis). Few alethinophidian snakes prey on arthropods, but the colubrines include the largest radiation of arthropod-eating snakes, the sonorines, with about a dozen genera, including the North American groundsnakes (Sonora), black-headed snakes (Tantilla), and shovel-nosed snakes (Chionactis). Sonorines are broadly distributed throughout the Americas, but they have their greatest diversity in the dry regions of southwestern North America. Another important cluster of genera includes the diverse African sandsnakes (Psammophis) and related species, including the Montpellier snake (Malpolon monspessulanus) of the Mediterranean region. Several genera of arboreal colubrines have independently evolved the so-called vinesnake morphology, with very narrow heads, slender bodies, and even behavioral modifications that allow them to blend into the surrounding vegetation. These include genera in the Neotropics (Oxybelis), Africa (Theletornis), and Southeast Asia (Ahaetulla). (Other vinesnakes have evolved in the subfamilies Xenodontinae and Lamprophiinae.) In addition to many small, burrowing species, the Colubrinae includes some giants among colubrids, such as the indigo snake (Drymarchon), tiger ratsnake (Spilotes), and bird snake (Pseustes) of the Americas, and the banded ratsnake (Ptyas) of Asia, which approaches or exceeds 10 ft (about 3 m) in length.

The Xenodontinae comprise another large colubrid subfamily, with a distribution limited to the New World. With about 90 genera and over 500 species, this group dominates the colubrid fauna of the Neotropics, where most of its diversity occurs. Two major groups have been identified, one centered in Central America and one in South America, although the two groups broadly overlap geographically, and a number of genera cannot be assigned to either of those two major clades. Some familiar North American species belong to the Xenodontinae, including the ring-necked snakes (Diadophis), wormsnakes (Carphophis), and mudsnakes (Farancia). Even more than the colubrines, the Xenodontinae encompass an extraordinary range of natural histories. Among the major themes are repeated invasions of aquatic, arboreal, and fossorial habitats, as well as specialization on any of a wide range of prey, including fishes, amphibians, earthworms, and terrestrial mollusks. A number of well-defined clades are recognized within the Xenodontinae. Among those in the South American group are the false pitvipers (Xenodon) and such related genera as the Neotropical hog-nosed snakes (Lystrophis) and Liophis. Many members of this group feed on frogs, including such highly toxic species as toads (Bufo) and poison frogs (Dendrobatidae). The North American hognosed snakes (Heterodon) are also xenodontines, but apparently represent an independent evolution of toad-eating habits. Other primarily South American groups include the pseudoboines, which include the mussurana (Clelia) and related genera, the diverse terrestrial to arboreal species of Philodryas, and the highly aquatic members of the genera Helicops and Hydrops. A substantial radiation from the South American clade occurs in the West Indies, and a few species are found on the Galápagos Islands. Some have evolved the vinesnake morphology, including Uromacer and Xenoxybelis. The Central American clade includes a very important radiation of predators on worms or terrestrial mollusks. Among them are worm-eaters, such as Geophis and Atractus, and the so-called snail-suckers, such as Dipsas and Sibon, which prey on snails and/or slugs. The snail-eating xenodontines strongly resemble the pareatines of Asia, both externally and in details of their skulls and jaw muscles, and they apparently use similar feeding mechanics to extract snails from their shells. Many xenodontines of both major clades are rear-fanged. A number of xenodontine species mimic venomous coralsnakes (Micrurus), as do several colubrines.

The final subfamily of colubrids is the Lamprophiinae, a more modest radiation in both numbers and distribution. The 44 genera and roughly 200 species of lamprophiines are limited to sub-Saharan Africa. Most are small to moderate-sized snakes, and many prey upon reptiles, including other snakes. Some are more specialized, however, including aquatic specialists such as Lycodonomorphus and Grayia, and prey specialists such as the slug-eaters (Duberria). An important radiation occurs on Madagascar, where members of this group dominate the snake fauna. Among that distinctive fauna are the Madagascan hog-nosed snakes (Lioheterodon) and the bizarre arboreal Madagascan vinesnakes (Langaha), which have a scaly proboscis on their snout.

Physical characteristics

Again, generalizations are difficult in light of the extraordinary diversity encompassed within this family. Compared with basal families and with boas and pythons, colubrids are characterized by the loss or simplification of many features. Notably, all vestiges of the hind limbs are absent in colubrids, and the coronoid bones of the lower jaws have been lost. Externally, most colubrids have relatively wider ventral scales and fewer rows of dorsal scales than boas and pythons. In addition, most colubrids possess a standard complement of enlarged scales on the head, including nine scales on the top of the head. That feature, like other external attributes, is shared with members of the Atractaspididae and Elapidae and even with some Viperidae, and at the same time is not seen in all members of the Colubridae. The vertebrae of colubrids are, in general, more slender and lightly built than those of basal snakes, boas, and pythons. In addition, the interconnecting chains of muscles that effect locomotion in snakes are longer in colubrids than in those other groups.

One important feature that distinguishes most colubrids is the presence of Duvernoy's glands, a pair of glands located on either side of the head behind the eye. These are the homologues (the evolutionary counterparts) of the venom glands of vipers, elapids, and Atractaspis. Although they are often described as modified salivary glands, they in fact are very different in both their tissue characteristics and their origin. The Duvernoy's glands are associated with the rear teeth of the maxillary bones, the major toothed bones of the upper jaws, and they secrete a complex mix of chemicals whose composition is still poorly understood. In some colubrids the secretion is known to serve as a slow-acting venom or as a digestive adjunct. The rear pair of maxillary teeth are often modified to assist with the delivery of secretion from Duvernoy's glands, and may be either enlarged, grooved, or both. That is generally known as the rear-fanged, or ophisthoglyphous, condition, although a variety of terms has been applied to specific conditions of the rear teeth. In most cases the secretion of Duvernoy's gland has no apparent effect on humans, but in some species it can cause local swelling. A few taxa, including the boomslang (Dispholidus) and twigsnake (Theletornis) of Africa and the Yamakagashi (Rhabdophis) of Asia, are capable of delivering a lethal bite to humans. The xenodontine genera Apostolepis and Elapomorphus resemble some aparallactine atractaspidids in approaching the front-fanged condition of elapid snakes, with large Duvernoy's glands and few teeth preceding the greatly enlarged rear fangs. Although Duvernoy's gland is found, to some degree, in most colubrids, it is not universally present. In some colubrids it may have been lost as a consequence of the evolution of constricting behavior, which constitutes an alternative mechanism for immobilizing prey. In other colubrids the enlarged rear maxillary teeth may serve a purely mechanical function. In some toad-eating snakes, such as hog-nosed snakes (Heterodon), those teeth may be used to deflate the prey, which in others, such as kukrisnakes (Oligodon), they are used to slice open the eggs of lizards and snakes.

Distribution

Members of the Colubridae occur worldwide, except Antarctica, the highest latitudes of North America and Eurasia, and the central and western regions of Australia. Only vipers extend farther north, in Scandanavia, than do colubrids. In Australia, unlike other regions, colubrids account for a minority of the snake fauna, with members of the Elapidae predominating.

Habitat

Colubrids occupy a wide array of habitats, and independent lineages have repeatedly entered the same habitat. It is impossible to know the ancestral habitat of the Colubridae. Although the earliest fossils have been allied with living terrestrial lineages, the vertebrae of most colubrids do not unambiguously reflect the species' habitat. Terrestrial species occur on all occupied continents and in all subfamilies except the Homalopsinae. Likewise, aquatic species abound in most subfamilies, and their morphologies range from minimally specialized to highly modified. Examples of the former include many members of the Natricinae, including the North American watersnakes (Nerodia) and Eurasian watersnakes (Natrix), as well as the African watersnakes (Lycodonomorphus) of the Lamprophiinae. The Xenodontinae include many aquatic taxa, from the relatively generalized Neotropical watersnakes (Helicops) to the more highly modified Neotropical swampsnake (Tretanorhinus), which has dorsally placed eyes and valvular nostrils. Some aquatic xenodontines, such as mudsnakes (Farancia) of North America and Hydrops and Pseudoeryx of South America, have rounded heads and smooth, shiny scales, and seem to be adapted for burrowing in aquatic habitats. The entire subfamily Homalopsinae is aquatic, and its members range from moderately specialized forms such as Enhydris and the puff-faced watersnake (Homalopsis) to extreme specialists such as the keel-bellied watersnake (Bitia) and the bizarre tentacled snake (Erpeton), which rarely leave the water. Homalopsines have valvular nostrils and mouths similar to those of seasnakes.

Some primarily terrestrial colubrids occasionally climb small shrubs, and even some relatively unmodified taxa, such as the ratsnakes (Elaphe) of the Colubrinae, are adept climbers of trees. More specialized arboreal species include the various vine-snakes of the Colubrinae, Xenodontinae, and Lamprophiinae, described above, and the nearly as specialized rough greensnake (Opheodrys aestivus), a North American colubrine. The Pareatinae are primarily arboreal, and the Colubrinae and Xenodontinae include many arboreal species in the tropics. Such species usually exhibit slender bodies, which may be laterally compressed. The most extreme condition occurs in the blunt-headed vinesnakes (Imantodes), Neotropical xenodontines that have extremely slender bodies and chunky heads. The Southeast Asian flyingsnakes (Chrysopelea) are arboreal colubrines that can flatten their bodies and glide from tree to tree.

Likewise, cryptozoic (hiding) and fossorial (burrowing) forms abound in most subfamilies. Aside from being relatively small, cryptozoic species are sometimes little modified morphologically, as in the colubrine North American ground-snakes (Sonora) and the xenodontine coffeesnakes (Ninia). Others are highly modified for burrowing, including the colubrine shovel-nosed snakes (Chionactis) of North America and shovel-snouted snakes (Prosymna) of Africa. Fossorial species abound in the Xenodontinae, including the Neotropical burrowing snakes (Geophis) of Central America and Apostolepis of South America. Such species often have pointed snouts, fused head scales, compact cranial bones, and smooth, shiny scales on the body. Even a few members of the Natricinae exhibit fossorial adaptations, such as the lined snake (Tropidoclonion) and rough earthsnake (Virginia striatula) of North America.

Behavior

As expected, behaviors are extremely diverse among Colubridae and generally poorly known, with the exception of a few common or unusual species. The behavior of a species often reflects its environment, and arboreal, cryptozoic, and fossorial species are especially difficult to study behaviorally. Defensive behavior, in particular, seems to reflect both coloration and habitat. Many species are cryptically colored (camouflaged) and, in the various vinesnakes, similarity to the snake's surroundings is enhanced by the narrow body and pointed head. More active defenses include threat displays, which may involve flattening the body, as in many North American watersnakes (Nerodia); spreading of a horizontal hood reminiscent of cobras, as seen in the xenodontine false water-cobras (Hydrodynastes); or vertical inflation of the neck, as in the colubrine tiger ratsnake (Spilotes). In general, horizontal displays characterize terrestrial species, whereas arboreal ones have vertical displays. Tail displays also occur in some species, such as the xendontine ring-necked snakes (Diadophis), in which the tail is upturned to show the bright ventral coloration and is moved in a distinctive spiral action. Other species gape when confronted by a predator and many bite, although others simply attempt to escape. Asian natricine snakes of the genera Rhabdophis and Balanophis have glands on the dorsal surface of their neck or along their entire back that exude a noxious compound when the snakes are threatened. Tail loss is rare among snakes, but a few taxa apparently lose the tail freely to escape predators, including the neck-banded snake (Scaphiodontophis), a Neotropical colubrine. Unlike the tails of some lizards, those of snakes do not regenerate if lost. Mimicry is common among snakes. Some species, such as the false pitvipers (Xenodon), mimic vipers, while in the Neotropics many species of xenodontines and a few colubrines mimic the elapid American coral snakes (Micrurus).

Colubrid snakes do not appear to be territorial. Instead, the males of some species, especially among the colubrines, are known to engage in ritual combat to obtain access to mates. Such combat generally resembles that of vipers and elapids, with the individuals intertwining their bodies and attempting to topple each other. That behavior may have served as the inspiration for the caduceus, the staff with entwining snakes that was said to have been carried by the god Hermes and that now is emblematic of the medical profession. In some species biting may also occur during combat. Species with male combat generally exhibit sexual size dimorphism in which males are larger than females, reflecting the fact that larger males generally are more successful in combat and therefore are favored to reproduce. Some other species exhibit the opposite pattern of sexual size dimorphism, in which females are larger than males. That condition reflects selection in which larger female size is associated with greater numbers of offspring.

Courtship behavior is known in a number of colubrid species, and it generally involves the male tongue-flicking and pressing his head along the back of the female. If the female is receptive, the male inserts one of his paired hemipenes into the female's cloaca to inseminate her. Males often locate females by following pheromone trails, a behavior mediated by the vomeronasal organ located in the roof of the mouth. That

organ receives cues from the environment by means of the tongue tips. In some species courting males aggregate around females and compete for matings, as in certain Canadian populations of the common gartersnake (Thamnophis sirtalis).

Feeding ecology and diet

Colubrids feed on a wide variety of prey. Some species are prey generalists, feeding on virtually any animals within an appropriate size range. The racer (Coluber constrictor), for example, is known to feed on a wide variety of prey, including mammals, lizards, frogs, baby turtles, and insects. Some wide-ranging species, such as the ring-necked snake (Diadophis punctatus), consume different prey in different parts of their range, while in others with varied diets, such as the common garter snake (Thamnophis sirtalis), prey preference is influenced by early experience with a particular prey. Location of prey frequently involves the use of chemical cues, which are picked up by the tongue and delivered to the vomeronasal organ. However, many terrestrial and arboreal snakes are also strongly dependent upon vision to locate prey.

More often, however, colubrids are prey specialists, preferring either a general class of prey, such as fishes, frogs, or mammals, or a very specific diet, such as lizard eggs or skinks. Unlike lizards, few snakes feed regularly on insects. Among colubrids, only a few lineages take large numbers of insects or other terrestrial arthropods, of which the sonorines are the largest. Even within that group, some (such as Sonora) take a variety of arthropods, whereas others specialize on particular arthropods, such as centipedes (Tantilla). Stenorrhina preys primarily upon scorpions, tarantulas, and grasshoppers. Some snakes specialize on prey of a certain shape. Often these are fossorial snakes, whose narrow heads limit them to relatively elongate prey. For smaller species these may be worms, whereas large species may feed on snakes or elongate lizards. Within the aquatic genus Farancia, the rainbow snake (F. erytrogramma) feeds mainly on eels, whereas the red-bellied mudsnake (F. abacura) feeds primarily on elongate aquatic amphibians, such as sirens (Siren). Eggs are a rich, if seasonal, source of food for many snakes. The arboreal cat-eyed snakes (Leptodeira), of the Neotropics, feed both on frogs and on frog eggs that are laid on vegetation overhanging water, such as those of the red-eyed treefrog (Agalychnis callidryas). The soft-shelled eggs of lizards and snakes are eaten by a variety of snakes, including the scarletsnake, Cemophora, a North American colubrine, the Asian kukrisnakes (Oligodon), and several Neotropical xenodontine genera, such as Umbrivaga and Enulius. An extreme case of specialization involves the egg-eaters (Dasypeltis), African colubrines that feed only on bird eggs. They consume eggs that may be several times the diameter of their own heads, forcing their nearly toothless jaws around the egg. Once in the esophagus, the eggs are cracked on ventral projections of the vertebrae; the shell is regurgitated and the liquid contents are swallowed. A few snakes possess hinged teeth, which fold back when their hard-bodied prey are consumed. Among these are several lineages of skink-eating snakes, including the neck-banded snake (Scaphiodontophis), a Neotropical colubrine, and some that feed on hard-shelled crayfish, including the striped crayfish snake (Regina alleni), a natricine from southeastern North America.

Reproductive biology

Although most species of colubrid snakes are oviparous, a large number of viviparous species are also known. Eggs may be laid in a hole or burrow in the ground or within rotting vegetation, where the heat generated by decomposition presumably speeds development. Viviparous species are especially prevalent at high latitudes and at high elevations, where females apparently can overcome the adverse effects of cold environmental temperatures on embryonic development by actively thermoregulating their own temperature and thus warming their embryos.

The size of a clutch or litter varies widely among colubrids. Small, fossorial oviparous species often lay only a few eggs (the wormsnakes, Carphophis, average about three per clutch), whereas larger terrestrial species often lay several times as many (for example, common kingsnakes, Lampropeltis getula, average about 10). In some species clutch size varies geographically, as in the Eastern racer (Coluber constrictor). Some species lay many more, such as the Eastern hog-nosed snake (Heterodon platirhinos), which averages more than 20 eggs per clutch, and the mudsnakes (Farancia), which average over 30. The females of several oviparous species of colubrids are reported to attend their clutches, and others are known to lay their eggs in communal oviposition sites. Likewise, litter size varies greatly among viviparous species. All of the thamnophiine natricines are viviparous, with the average number of young varying from about seven in the North American earthsnakes (Virginia) to almost 30 in the Plains garter snake (Thamnophis radix) and almost 50 in the diamond-backed watersnake (Nerodia rhombifera).

Most colubrid snakes reproduce annually, even in tropical regions, and reproduction may be timed to the seasonal patterns of temperature or rainfall. The embryos of both oviparous and viviparous snakes are well provisioned with yolk, although in some viviparous species a placenta permits the transfer of additional nutrients from mother to embryo. Even in oviparous colubrids, embryonic development usually begins well before the eggs are laid, and the embryos are already about one-third of the way through development by the time of oviposition.

Conservation status

The 2002 IUCN Red List includes 36 colubrid species. One species, Alsophis sanctaecrucis, is categorized as Extinct. In addition, 6 species are listed as Critically Endangered; 7 as Endangered; 8 as Vulnerable; 4 as Lower Risk/Near Threatened; and 10 as Data Deficient.

Very few colubrids are legally protected at either the national or international levels, although more regional regulations protect a few more. No colubrid species appear on Appendix I of CITES, only four appear on Appendix II, and three appear on Appendix III. As with most organisms, habitat destruction is probably the leading threat to colubrid snakes throughout most of their range. In addition, however, collection for the pet trade has contributed to the decline of some species, such as the Eastern indigo snake (Drymarchon corais couperi), and some species may be at risk due to their use in the skin trade and other commerce.

Overwhelmingly, it is humans who pose an ongoing threat to many colubrid snakes. However, one species, the brown treesnake (Boiga irregularis), has itself become a severe threat to the native fauna of the Pacific island of Guam. The accidental introduction of this adaptable predator to the island following World War II, apparently as stowaways on military transports, has resulted in the decimation of the native lizards and birds of the island and has resulted in the collapse of the natural food web. Efforts are under way to control this species and to recover the populations of those birds that have not already been completely extirpated.

Significance to humans

Colubrid snakes appear to figure in human commerce in two primary ways. First, many species are sold in the pet trade, including large numbers of wild-caught individuals of many species. Several groups of colubrids have become sufficiently popular that they now are bred in captivity in large numbers. Among the latter are the cornsnake (Elaphe guttata) and several species of kingsnakes (Lampropeltis). Although most species are too small to be useful as leather, a few colubrids are exploited in the skin trade, including the large Asian ratsnakes (Ptyas). Recently a large trade in aquatic colubrids of the subfamily Homalopsinae has been documented in Cambodia, and much of that trade involves the preparation of skins for leather. In addition, however, snakes are used as food for humans and are also fed to farm-raised crocodiles that are in turn used for leather. The magnitude of the trade was enormous, with an estimated 4,000–8,500 snakes per day traded at one port during peak periods. That catch is likely to be unsustainable.

Species accounts

List of Species

Brown treesnake

Boiga irregularis

subfamily

Colubrinae

taxonomy

Coluber irregularis Merrem, 1802, Bechstein.

other common names

None known.

physical characteristics

This snake is about 4.5–6.5 ft (1.4–2 m) in length. It has a slender body, very narrow neck, rounded head, and large eyes. It is tan to brown in color with irregular, darker brown, transverse markings.

distribution

The brown treesnake is found in Indonesia, New Guinea, Solomon Islands, and northern Australia. It has been introduced on Guam.

habitat

This snake is primarily arboreal, but it also forages terrestrially. It occurs in a range of habitats, including forests, swamps, and coastal regions.

behavior

The brown treesnake is primarily nocturnal. It strikes defensively when threatened.

feeding ecology and diet

This species feeds on a variety of vertebrates, primarily lizards, birds, and mammals.

reproductive biology

The brown treesnake is oviparous, laying about a dozen eggs per clutch.

conservation status

Not threatened. On Guam, where the species has been introduced, it is implicated in the extinction of several species of vertebrates, including most of the native birds.

significance to humans

There is concern that this species may spread to other Pacific Islands, prompting security measures on some islands, including Hawaii, in an attempt to prevent its introduction.

Smooth snake

Coronella austriaca

subfamily

Colubrinae

taxonomy

Coronella austriaca Laurenti, 1768. Three subspecies are recognized.

other common names

French: Couleuvre lisse; German: Glattnatter.

physical characteristics

Adults reach about 24 in (60 cm) in length. This is a shiny, grayish or reddish brown snake with ill-defined, paired blotches down the back.

distribution

Europe (including southern England) and western Asia, from Scandinavia to northern Spain and east to Kazakhstan and northern Iran.

habitat

Fairly dry, open, rocky habitats are favored, including stone walls. In England this species favors heathlands, finding shelter under rocks and logs.

behavior

The smooth snake forages diurnally.

feeding ecology and diet

This snake feeds primarily on lizards, but other small vertebrates are also taken. The prey is constricted.

reproductive biology

This species is viviparous, giving birth to about four to 15 young.

conservation status

Numbers reportedly have declined greatly in England and elsewhere in its European range. Although not listed by the IUCN, the species is fully protected in Europe, being listed in Appendix II of the Bern Convention of European Wildlife and Natural Habitats and on Annex IV of the European Union Habitat and Species Directive.

significance to humans

The smooth snake is apparently a sensitive indicator of the health of heathlands in southern England.

Common egg-eater

Dasypeltis scabra

subfamily

Colubrinae

taxonomy

Coluber scaber Linnaeus, 1758, Indiis. Two subspecies are sometimes recognized.

other common names

English: African egg-eater, rhombic egg-eater.

physical characteristics

This snake is about 20–35 in (50–90 cm) in length. It is a very slender snake with a narrow head; the dorsal scales are keeled, and the keels are serrated on the lower lateral scales. The color varies but is usually gray or brown, with prominent dark blotches down the center of the back and narrower ones on the sides. The jaws are nearly toothless, the skin of the neck is capable of an astonishing degree of stretching, and the anterior vertebrae are modified to crack the shells of bird eggs.

distribution

Widely distributed throughout sub-Saharan Africa.

habitat

The common egg-eater occupies a range of habitats, exclusive of the driest deserts and wettest tropical forests.

behavior

The common egg-eater mimics various species of vipers in different parts of its range. Mimicry of the saw-scaled viper (Echis carinatus) involves not only appearance but behavior. Like that viper, the egg-eater throws its body into a series of curved loops and rubs the serrated lateral scales against each other to produce a hissing sound.

feeding ecology and diet

This snake feeds exclusively on bird eggs, and its morphology is highly modified for that diet. The head is forced over an egg, which may be several times the diameter of the head, and the egg is cracked using modified ventral processes (hypapophyses) of the anterior vertebrae, which actually penetrate the esophagus. The liquid contents of the egg are swallowed, and the shell is crushed and regurgitated. The egg-eater feeds heavily in the spring and summer, when birds are nesting.

reproductive biology

The common egg-eater is oviparous, with a clutch size of six to 25 eggs.

conservation status

Not listed by the IUCN.

significance to humans

The common egg-eater may be mistaken as a venomous snake, due to its mimicry of several species of vipers

Boomslang

Dispholidus typus

subfamily

Colubrinae

taxonomy

Bucephalus typus Smith, 1829, Old Latakoo, South Africa. Two or three subspecies are recognized.

other common names

French: Serpent d'arbre du Cap; German: Boomslang.

physical characteristics

The boomslang is about 4 ft (1.25 m) in length. It is a long, slender snake with distinctive oblique dorsal scales. Its color is highly variable, ranging from nearly black to bright green and even reddish; some individuals have black scales with a bright yellow spot in the center. Males are more brightly colored than females. The head is large and the eyes are prominent.

distribution

Ranges widely throughout sub-Saharan Africa.

habitat

This species occurs in a wide variety of habitats, including forest and savanna.

behavior

The boomslang is highly arboreal.

feeding ecology and diet

This snake forages diurnally, feeding on a variety of arboreal prey, especially birds and chameleons.

reproductive biology

The boomslang is oviparous, with a clutch size of about a dozen eggs.

conservation status

Not listed by the IUCN.

significance to humans

The boomslang is one of the few colubrid snakes capable of producing a lethal bite in humans. The venom, which is injected through very long rear fangs, acts slowly to impair the blood's ability to clot, resulting in death by hemorrhage. The prominent herpetologist Karl P. Schmidt died from the bite of a boomslang in 1957.

Indigo snake

Drymarchon corais

subfamily

Colubrinae

taxonomy

Coluber corais Boie, 1827, America. Eight subspecies are recognized, and some workers believe that several separate species should be recognized.

other common names

English: Blacktail, cribo; Spanish: Cola sucia.

physical characteristics

This very large colubrid may reach almost 10 ft (3 m) in length. It has large, shiny, slightly oblique dorsal scales. Its color varies geographically. D. c. couperi, of the southeastern United States, is jet black with a reddish throat. Tropical subspecies may be black, gray, brown, or yellow, sometimes with a sharply contrasting tail.

distribution

Ranges from the southeastern United States to northern Argentina.

habitat

In the southeastern United States, this species prefers environments with sandy soils, such as pine savanna and scrub. Tropical

populations occupy a wider range of habitats, from moist forest to savanna and thorn forest. The species is frequently found near water.

behavior

The indigo snake is diurnal, foraging actively over large areas.

feeding ecology and diet

A wide variety of prey are consumed, including other fishes, frogs, turtles, birds, and mammals. Other snakes appear to comprise a substantial proportion of the diet, including pitvipers. It does not constrict its prey but simply overpowers it.

reproductive biology

The indigo snake is oviparous, with a clutch size of about four to 12. Hatchlings are large, sometimes over 2 ft (60 cm).

conservation status

This species is not listed by the IUCN. However, in the southeastern United States, the eastern indigo snake (D. c. couperi) is listed as Threatened by the U.S. Fish and Wildlife Service; it is also listed by several states. The subspecies is highly prized in the pet trade, and illegal collecting continues to pose a threat. The species also is a frequent inhabitant of the burrows dug by gopher tortoises (Gopherus polyphemus), as is the eastern diamondback rattlesnake (Crotalus adamanteus). Rattlesnakes are collected in some regions for "rattlesnake round-ups" or for their skins, and collection often involves pouring gasoline down a tortoise burrow. That action can incidentally harm indigo snakes. Finally, this subspecies is strongly affected by the rapid residential and commercial development of its habitat in the southeastern United States.

significance to humans

Indigo snakes are highly valued as pets, especially D. c. couperi. Some individuals now are being produced through captive breeding.

Milksnake

Lampropeltis triangulum

subfamily

Colubrinae

taxonomy

Coluber triangulum Lacépède, 1788, America. Twenty-five subspecies are recognized, and it is likely that this species ultimately will be divided into several separate species.

other common names

English: Scarlet kingsnake (for subspecies L. t. elapsoides); French: Couleuvre tachetée; Spanish: Culebra-real coralillo.

physical characteristics

This snake varies greatly in size and appearance across its broad geographic range, as reflected in the large number of subspecies recognized. Adult length varies from about 20–60 in (50–152 cm), depending upon the population. The usual color pattern is one of alternating bands of red-black-yellow/white-black-red. However, some populations have red blotches rather than bands, and one subspecies is melanistic (virtually all black). The scales are smooth and shiny.

distribution

This species has a wide range, from southeastern Canada to western Ecuador and northern Venezuela.

habitat

Habitat varies across the wide range of this species. It generally occupies forested environments, but in some regions it can also be found in open prairies. In various parts of its range this species frequently occupies rocky slopes.

behavior

The milksnake is essentially terrestrial (although L. t. elapsoides sometimes takes shelter beneath the bark of standing dead pine trees), and activity is largely nocturnal.

feeding ecology and diet

The diet varies by region but often includes lizards (especially skinks), snakes, and small mammals.

reproductive biology

Milksnakes are oviparous, laying an average of about 10 eggs per clutch, although that number may vary geographically.

conservation status

Not listed by the IUCN, although in some regions there may be substantial pressure from collection for the pet trade.

significance to humans

The common name of the species derives from an early myth that the species sucks milk from cows. That erroneous idea presumably derived from the discovery of milksnakes near barns, where they may have been feeding on mice. This species is highly valued in the pet trade, and many subspecies are now being bred in captivity for sale.

Dog-faced watersnake

Cerberus rynchops

subfamily

Homalopsinae

taxonomy

Hydrus rynchops Schneider, 1799, Ganjam, India. Two subspecies are recognized.

other common names

English: Bockadam.

physical characteristics

This snake is about 24 in (60 cm) in length. It is a slender, grayish to reddish snake with a narrowly triangular head and dorsal eyes and nostrils.

distribution

This is a coastal species found from western India through Southeast Asia, the Philippines, and Indonesia, to northern Australia.

habitat

This species occupies coastal mangrove forests and estuaries, where it is often found on mud flats.

behavior

The dog-faced watersnake forages in the water and on mud flats, where it moves by sidewinding. It is reported to release a foul-smelling musk for defense.

feeding ecology and diet

This species feeds primarily upon fishes.

reproductive biology

This snake is viviparous, giving birth to about eight young.

conservation status

Not listed by the IUCN, although coastal environments in general are subject to increasing pressure from expanding human populations.

significance to humans

None known.

Tentacled snake

Erpeton tentaculatus

subfamily

Homalopsinae

taxonomy

Erpeton tentaculatus Lacépède, 1800, locality unknown.

other common names

None known.

physical characteristics

One of the most distinctive snakes, this species is 20 in (50 cm) in length and is readily identifiable by the paired, scaly appendages that project from the front of the snout. The head and body are extremely flat, the nostrils are valvular and dorsal in position, and the color may be light brown with darker stripes or very dark with lighter brown mottling.

distribution

Central and southern Thailand, and southern Cambodia and Vietnam.

habitat

Tentacled snakes are found in ponds and slow-moving streams.

behavior

This snake is entirely aquatic, lying quietly among submerged vegetation waiting for prey. The flattened body is very stiff, capable of bending laterally but exhibiting little vertical flexibility.

feeding ecology and diet

These snakes are ambush predators of fishes.

reproductive biology

This species is viviparous.

conservation status

Not listed by the IUCN.

significance to humans

Tentacled snakes appear from time to time in the pet trade. In some regions they are erroneously regarded as dangerously venomous.

Common slug-eater

Duberria lutrix

subfamily

Lamprophiinae

taxonomy

Coluber lutrix Linnaeus, 1758, Indiis. Six subspecies recognized.

other common names

None known.

physical characteristics

The common slug-eater is a small snake, about 14 in (35 cm) in length, with a thick body and a narrow head. The scales are smooth, and the dorsal surface is brown or reddish; the ventral color is lighter.

distribution

Eastern Africa from Ethiopia to the Cape.

habitat

This snake occupies savannas and bush habitats.

behavior

This species coils tightly when threatened.

feeding ecology and diet

The common slug-eater forages in moist situations, preying primarily on slugs. Land snails are also eaten.

reproductive biology

This species is viviparous, giving birth to about 10 relatively large young per litter.

conservation status

Not threatened.

significance to humans

None known.

Cape filesnake

Mehelya capensis

subfamily

Lamprophiinae

taxonomy

Heterolepis capensis Smith, 1847, Eastern districts of Cape Province, South Africa. Three subspecies are recognized.

other common names

German: Kap-Feilennatter.

physical characteristics

As with other filesnakes, the body of this species has the distinctive triangular cross-section that inspired the common name. The shape results from highly modified vertebrae, which have long processes that project dorsally and laterally. Reaching about 60 in (1.5 m) in length, this species has narrow, keeled dorsal scales with patches of bare skin between them and an enlarged row of scales down the center of the back. The dorsal color is gray or dark brown, with a white or yellow mid-dorsal stripe.

distribution

Ranges through most of sub-Saharan Africa, from Cameroon and Somalia to the Cape.

habitat

The Cape filesnake occupies a variety of habitats but is especially prevalent in savannas.

behavior

This is a terrestrial species that is active nocturnally.

feeding ecology and diet

Although the Cape filesnake feeds on a variety of vertebrates, including lizards and mammals, snakes are the preferred prey. This species constricts its prey and may consume snakes that are very long relative to its own body.

reproductive biology

This species is oviparous, usually laying about six eggs. The hatchlings are large, about 15.8 in (40 cm) in length.

conservation status

Not threatened.

significance to humans

None known.

Yamakagashi

Rhabdophis tigrinus

subfamily

Natricinae

taxonomy

Tropidonotus tigrinus Boie, 1826. Two subspecies are recognized.

other common names

English: Tiger watersnake.

physical characteristics

This is a rather slender snake that attains a length of about 40 in (1 m). Color varies, but most specimens are drab green to yellow, with red skin between the scales of the neck. Young have a bright light ring around the neck. The dorsal scales are keeled, and enlarged scales on the neck overlie special nuchal glands.

distribution

Widely distributed in eastern Asia, including much of China, Korea, and Japan.

habitat

This snake is terrestrial but is generally found in association with water, including rice paddies.

behavior

The defensive behavior of this snake is very unusual. When threatened by a predator, the snake arches its neck toward the attacker and releases the contents of paired nuchal glands that lie in the dorsal skin. The product of those glands is distasteful and irritating to the eyes and contains compounds similar to those found in the skin glands of toads.

feeding ecology and diet

This species feeds almost entirely on frogs and toads, although it occasionally eats fishes.

reproductive biology

This snake is oviparous, laying about a dozen eggs per clutch.

conservation status

Not listed by the IUCN. At one site in Japan, this species is reported to have declined due to changes in agricultural practices, including the use of pesticides and chemical fertilizers, which may have reduced the numbers of frogs.

significance to humans

Although this snake is reluctant to bite defensively, the bite has been known to cause fatalities in humans. The venom acts very slowly, inhibiting the ability of the blood to clot and causing death by hemorrhage.

Common garter snake

Thamnophis sirtalis

subfamily

Natricinae

taxonomy

Coluber sirtalis Linnaeus, 1758, Canada. Eleven subspecies are recognized.

other common names

French: Couleuvre rayèe, serpent-jarretière; German: Gewöhnliche Strumpfbandnatter; Spanish: Culebra-listonada común.

physical characteristics

The common garter snake is a relatively slender snake generally reaching about 28 in (70 cm) in length. Color varies greatly across the wide geographic range of this species, but in most populations the snake exhibits three longitudinal yellow stripes. The ground color may be dark brown, olive green, or red, sometimes with black patches.

distribution

This species is widely distributed across North America, including the eastern half of the continent, the northern Great Plains and northern Rocky Mountains, and the Pacific Coast.

Some Canadian populations extend far north, one reaching the southern Northwest Territories.

habitat

Common garter snakes are found in a wide variety of habitats, including marshes, fields, woodlands, and forest edges. This species is often found in association with water.

behavior

In general this snake is diurnally active, with a long activity season. It is active year round in the southern part of the range, and even at extreme northern localities it has been reported to be active for five months out of the year. Individuals in northern populations may travel long distances from their hibernation sites to their summer foraging habitats.

feeding ecology and diet

This species forages actively on a wide variety of prey, including both vertebrates and invertebrates. Common prey include earthworms, fishes, and frogs, but a host of other prey also are eaten, occasionally including small mammals or birds.

reproductive biology

This snake is viviparous, with litter size varying geographically. The usual litter size is about 10–15 young, although lower numbers are common in some northern populations, and an average of over 30 was recorded for a population in Maryland. Populations in Manitoba, Canada, are well known for the enormous aggregations of males seeking to mate upon emergence from hibernation. The males, which are smaller, emerge earlier, so females are courted by large numbers of waiting males.

conservation status

Not listed by the IUCN. The San Francisco garter snake (T. s. infernalis, previously known as T. s. tetrataenia) is the only snake in the United States listed as Endangered by the U.S. Fish and Wildlife Service. Habitat loss is primarily responsible for its decline. In Manitoba, Canada, where the red-sided garter snake (T. s. parietalis) aggregates by the thousands in communal hibernacula, the populations were once threatened by overcollection for commercial purposes. A ban on export of garter snakes from Manitoba was imposed in 1991.

significance to humans

Because of their abundance and ease of maintenance in captivity, common garter snakes are used for a variety of laboratory studies and are also maintained as pets.

Mussurana

Clelia clelia

subfamily

Xenodontinae

taxonomy

Coluber clelia Daudin, 1826, Surinam. Three or four subspecies are recognized.

other common names

Spanish: Culebrera, sumbadora.

physical characteristics

This is a large species, reaching over 6 ft (2 m) in length. Adults are uniform shiny black or dark gray dorsally, and

lighter ventrally. Juveniles are very different, having a bright red body with black tips on the dorsal scales, a broad cream collar, and a black snout.

distribution

Central and South America, from Guatemala and Belize to northern Argentina.

habitat

The mussurana is an occupant of both forested and open habitats, including marshes.

behavior

This active species largely forages nocturnally, but it can also be found abroad during the day.

feeding ecology and diet

Snakes are the preferred prey of this species, including pitvipers of the genus Bothrops, the lanceheads. Lizards and mammals are also eaten. This powerful snake combines constriction with rear-fanged envenomation.

reproductive biology

This snake is oviparous, laying clutches of about 10–20 eggs.

conservation status

Not listed by the IUCN. This species is listed on Appendix II of CITES, one of the few colubrids to receive such protection.

significance to humans

The mussurana is highly regarded within its range for its tendency to prey on venomous snakes. Protection under CITES presumably reflects a belief that this species might be desirable in the pet trade, although similar protection is not afforded countless species of other tropical colubrids.

Amazonian snail-eater

Dipsas indica

subfamily

Xenodontinae

taxonomy

Dipsas indica Laurenti, 1768, Ceylon (in error). Five subspecies are recognized.

other common names

None known.

physical characteristics

This is a slender snake about 28 in (70 cm) in length, with a laterally compressed body and a row of enlarged mid-dorsal scales. The body is gray to brown with large, dark brown blotches arranged in pairs on the sides. In some populations the edges of blotches may be somewhat irregular.

distribution

Found in tropical South America, from the Amazon Basin to Bolivia and northern Argentina.

habitat

This species occurs in both primary and secondary forest.

behavior

This snake is highly arboreal, foraging at night.

feeding ecology and diet

The Amazonian snail-eater feeds on snails, which it extracts from the shell. After the snake seizes the exposed body of a snail, the slender lower jaws of the snake are drawn into the shell as the snail retracts. The snake then slowly pulls on the soft body of the snail with its lower jaws, eventually tearing the body away from the shell, which is discarded.

reproductive biology

This oviparous species presumably resembles other species of Dipsas, which apparently lay very small clutches, as do some other slender arboreal snakes.

conservation status

Not listed by the IUCN, although it is clearly dependent upon tropical forest habitat, which is being cleared for timber and agriculture in many regions.

significance to humans

None known.

Eastern hog-nosed snake

Heterodon platirhinos

subfamily

Xenodontinae

taxonomy

Heterodon platirhinos Latreille, 1801, vicinity of Philadelphia.

other common names

English: Hissing adder, puff adder, spreading adder; French: Hétérodon commun; German: Gewöhnliche hakennatter.

physical characteristics

This is a stout-bodied snake, usually about 30 in (75 cm) in length, with a broad head and a distinctive, upturned snout. The keeled dorsal scales are arranged in oblique rows. The coloration is highly variable, often yellow, orange, or olive green, with dark brown dorsal and lateral blotches. Some individuals become melanistic (entirely black), especially in the southeastern United States.

distribution

Widely distributed across eastern and central North America, including southern Ontario, Canada.

habitat

This species occurs in a range of environments, including drier forests, but it prefers open habitats, generally with well-drained, sandy soils.

behavior

The Eastern hog-nosed snake has a diverse repertoire of defensive behaviors, some of which have given rise to colorful common names. When first approached by a predator, this species flattens its head and spreads the ribs of its neck to form a broad hood, while hissing loudly. The snake may raise its head and even strike, although the species almost never bites. If that display of bravado fails and the predator persists, the snake rolls on its back, usually with its mouth agape and its tongue hanging out, apparently feigning death. If turned right side up, the snake immediately rolls over on its back again, remaining in that position until the threat has passed.

feeding ecology and diet

Most populations of these snakes feed overwhelmingly on toads (Bufo), although other frogs may also be eaten, as well as occasional salamanders and even mammals. The snakes have been reported to use the upturned snout to excavate toads from sandy soils. The maxillary bone is highly mobile and has a pair of greatly enlarged rear teeth that apparently help to deflate toads that have puffed themselves up with air to resist being swallowed.

reproductive biology

This snake is oviparous, laying relatively large clutches of eggs (generally about 20, although much larger clutches have been reported).

conservation status

Not listed by the IUCN, although loss of habitat, declines in amphibian populations, and the threatening defensive behavior of this species (its stout body form also resembles that of pitvipers) probably make its populations vulnerable to human impact.

significance to humans

None known.

Northern cat-eyed snake

Leptodeira septentrionalis

subfamily

Xenodontinae

taxonomy

Dipsas septentrionalis Kennicott in Baird, 1859, Matamoros, Tamaulipas, Mexico and Brownsville, Texas. Five subspecies are recognized.

other common names

Spanish: Culebra destinida, culebra nocturna.

physical characteristics

This is a slender snake about 33 in (85 cm) long, with a moderately wide head and large eyes with vertical pupils. In general, the color pattern is brown with irregular, darker brown spots. However, the pattern varies considerably over the range of the species. In some regions the dark blotches extend fully across the body, whereas in others the dark markings are limited to small, irregular spots down the middle of the back.

distribution

Distributed widely through the northern Neotropics, from southern Texas and Sinaloa, Mexico, to western Venezuela and northwestern Peru.

habitat

The northern cat-eyed snake is primarily an inhabitant of moist forests, but it also occupies drier habitats in western Mexico and Peru.

behavior

This species is primarily arboreal, but it also engages in terrestrial activity, especially in drier portions of its range. Although it is rear-fanged, this species typically does not bite defensively when captured.

feeding ecology and diet

Frogs are the preferred prey of this species, which often forages among large choruses of calling males. Where frogs lay eggs on vegetation overhanging water, as in the case of the leaf frogs (Agalychnis), cat-eyed snakes also consume the eggs, pushing their faces into the mass of egg jelly to reach the developing embryos. In addition, lizards and even a snake have been reported as occasional prey.

reproductive biology

This snake is oviparous, laying about 10 eggs per clutch.

conservation status

Although not listed by the IUCN, this species is listed as Threatened by the Texas Parks and Wildlife Department, reflecting its very limited range at the southern tip of that state.

significance to humans

Before the advent of effective fumigation, snakes of the genus Leptodeira frequently stowed away in bunches of bananas, arriving alive at ports such as New York City.

Resources

Books

Branch, Bill. Field Guide to Snakes and Other Reptiles of Southern Africa. 3rd edition. Sanibel Island, FL: Ralph Curtis Books, 1998.

Cadle, John E., and Harry W. Greene. "Phylogenetic Patterns, Biogeography, and the Ecological Structure of Neotropical Snake Assemblages." In Species Diversity in Ecological Communities: Historical and Geographical Perspectives, edited by Robert E. Ricklefs and Dolf Schluter. Chicago: University of Chicago Press, 1993: 281–293.

Greene, Harry W. Snakes: The Evolution of Mystery in Nature. Berkeley: University of California Press, 1997.

Lee, Julian C. The Amphibians and Reptiles of the Yucatán Peninsula. Ithaca, NY: Cornell University Press, 1996.

Pough, F. Harvey, Robin M. Andrews, John E. Cadle, Martha L. Crump, Alan H. Savitzky, and Kentwood D. Wells. Herpetology. 2nd edition. Upper Saddle River, NJ: Prentice Hall, 2001.

Rossman, Douglas A., Neil B. Ford, and Richard A. Seigel. The Garter Snakes: Evolution and Ecology. Norman: University of Oklahoma Press, 1996.

Shine, Richard. "The Evolution of Viviparity in Reptiles: An Ecological Analysis." 605–694. In Biology of the Reptilia, Volume 15, Development B, edited by Carl Gans and Frank Billett. New York: John Wiley & Sons, 1985.

——. "Parental Care in Reptiles." In Biology of the Reptilia. Vol. 16, Ecology B: Defense and Life History, edited by Carl Gans and Raymond B. Huey. New York: Alan R. Liss, 1988: 275–329.

——. Australian Snakes: A Natural History. Ithaca, NY: Cornell University Press, 1991.

Zug, George R., Laurie J. Vitt, and Janalee P. Caldwell. Herpetology: An Introductory Biology of Amphibians and Reptiles. 2nd edition. San Diego: Academic Press, 2001.

Periodicals

Cadle, John E. "Molecular Systematics of Neotropical Xenodontine Snakes. III. Overview of Xenodontine Phylogeny and the History of New World Snakes." Copeia 1984 (1984): 641–652.

Cadle, John E. "Phylogenetic Relationships Among Advanced Snakes: A Molecular Perspective." University of California Publications in Zoology 119 (1988): 1–70.

——. "The Colubrid Radiation in Africa (Serpentes: Colubridae): Phylogenetic Relationships and Evolutionary Patterns Based on Immunological Data." Zoological Journal of the Linnean Society 110 (1994): 103–140.

Fritts, Thomas H., and Gordon H. Rodda. "The Role of Introduced Species in the Degradation of Island Ecosystems: A Case History of Guam." Annual Review of Ecology and Systematics 29 (1998): 113–140.

Gyi, Ko Ko. "A Revision of Colubrid Snakes of the Subfamily Homalopsinae." University of Kansas Publications, Museum of Natural History 20 (1970): 47–223.

Karns, Daryl R., Harold K. Voris, Tanya Chan-ard, Jeffrey C. Goodwin, and John C. Murphy. "The Spatial Ecology of the Rainbow Water Snake, Enhydris enhydris (Homalopsinae) in Southern Thailand." Herpetological Natural History 7 (2000): 97–115.

Kraus, Fred, and Wesley M. Brown. "Phylogenetic Relationships of Colubrid Snakes Based on Mitochondrial DNA Sequences." Zoological Journal of the Linnean Society 122 (1998): 455–487.

Lopez, T. J., and L. Maxson. "Mitochondrial DNA Sequence Variation and Genetic Differentiation Among Colubrine Snakes (Reptilia: Colubridae: Colubrinae)." Biochemical Systematics and Ecology 23 (1995): 487–505.

Shine, Richard. "Strangers in a Strange Land: Ecology of Australian Colubrid Snakes." Copeia 1991 (1991): 120–131.

——. "Sexual Size Dimorphism in Snakes Revisited." Copeia 1994 (1994): 326–346.

Stuart, Bryan L., Jady Smith, Kate Davey, Prom Din, and Steven G. Platt. "Homalopsine Watersnakes: The Harvest and Trade from Tonle Sap, Cambodia." TRAFFIC Bulletin 18 (2000): 115–124.

Zaher, Hussam. "Hemipenial Morphology of the South American Xenodontine Snakes, with a Proposal for a Monophyletic Xenodontinae and a Reappraisal of Colubroid Hemipenes." Bulletin of the American Museum of Natural History 240 (2000): 1–168.

Other

European Molecular Biology Laboratory. The EMBL Reptile Database. Family Colubridae (Colubrids). June 1, 2002 [cited October 31, 2002]. <http://www.embl-heidelberg.de/uetz/families/Colubridae.html>

Alan H. Savitzky, PhD