Vipers and pitvipers

(Viperidae)

Class Reptilia

Order Squamata

Suborder Serpentes

Family Viperidae

Thumbnail description
Small to large venomous snakes with hollow fangs attached to shortened, movable maxillary bones

Size
ca. 1–11.8 ft (30–360 cm)

Number of genera, species
36 genera; 256 species

Habitat
Deserts, steppes, mountains, forests, meadows, and savannas

Conservation status
Critically Endangered: 7 species; Endangered: 4 species; Vulnerable: 7 species; Data Deficient: 1 species

Distribution
Africa, Europe, Asia, North America, Central America, and South America

Evolution and systematics

Researchers have devoted considerable effort to reconstructing the phylogenetic history of the Viperidae, and, consequently, extensive revision of the classification of these snakes was done throughout the end of the twentieth century and has continued into the twenty-first century. Monophyly of the Viperidae is well supported by molecular and anatomical data. Available evidence suggests that the Viperidae is the most basal family of the Colubroidea, which also includes the Colubridae, Elapidae, and Atractaspididae. Four subfamilies are recognized.

The Causinae includes a single genus, Causus, with six species; the Viperinae includes 12 genera with 75 species; the Azemiopinae contains a single genus and species (Azemiops feae); and the pitvipers are classified in the Crotalinae, in which 22 genera and 174 species are recognized. With the possible exception of the Viperinae, the monophyly of each viperid subfamily is well supported by anatomical and molecular data. A potential synapomorphy of the Viperinae is the ventral course of the facial carotid artery, providing at least some support for the monophyly of this subfamily. The Causinae is thought to be sister to either all other viperids or only the Viperinae. The Azemiopinae is sister to the Crotalinae. As of 2002 almost all genera and subgenera recognized are monophyletic, although relationships among genera are not yet resolved fully.

Viperinae consists of Vipera, Macrovipera, Pseudocerastes, Eristicophis, Daboia, Echis, Cerastes, Atheris, Bitis, Proatheris, Adenorhinos, and Montatheris. The Eurasian genus Vipera is divided into the subgenera Vipera, Pelias, Montivipera, and Acridophaga, each with an evolutionary history that can be traced back to the Miocene through the fossil record or "molecular clock" calibrations. It is the same with the African genus Bitis, which is divided into the subgenera Bitis, Macrocerastes, Calechidna, and Keniabitis, each with its own evolutionary history, as inferred from molecular data. Unfortunately, there are no viper fossils known from tropical Africa. The genera of Old World pitvipers are Calloselasma, Deinagkistrodon, Ermia, Gloydius, Hypnale, Ovophis, Protobothrops, Triceratolepidophis, Trimeresurus, and Tropidolaemus, and the genera of New World pitvipers are Agkistrodon, Atropoides, Bothriechis, Bothriopsis, Bothrocophias, Bothrops, Cerrophidion, Crotalus, Lachesis, Ophryacus, Porthidium, and Sistrurus.

The region of origin for viperids remains undetermined. The earliest fossil specimens of this family are known from the Lower Miocene (ca. 20 million years ago) of Europe and West Asia. These findings are well documented, but there are no fossil records from the Oligocene, and there is a general opinion that the viperines arose somewhere else. The origin of African viperines has been dated to at least 50 million years before the present based on molecular evidence, and there is much support for a tropical African origin of the Viperidae.

The striking examples of convergent evolution between the Asian and American pitviper radiations had long obscured attempts to understand the phylogeny of these snakes; however, data from mitochondrial DNA sequences strongly suggest that pitvipers originated in Asia, and these findings are consistent with other lines of evidence. For example, the closest living relative of all pitvipers, Azemiops feae, is an Asian species. The earliest known fossil pitviper from the New World is from the Miocene. All New World pitvipers are descended

from a single pitviper species that extended its range across the Bering Land Bridge into North America. Phylogenetic studies suggest that the original American pitviper resembled Gloydius blomhoffi in many respects.

Physical characteristics

In vipers or adders (Viperinae) and pitvipers (Crotalinae), the head is roughly triangular and is distinct from the rest of the body. The head bears nine symmetrical plates (as in Agkistrodon and Gloydius), fragmented head plates (as in many Vipera), or numerous small scales (as in Bitis and Ophryacus). The pupils are usually vertical and elliptical. All the face bones are movable. Each of the two shortened, retractile upper jawbones (maxillae) bears only the tubular venom fang (which can be activated only for a short period of time) and often one to several significantly smaller reserve teeth of various sizes, none being a firmly positioned poison fang. The tail is short, and the male copulatory organ is bifid (forked).

Viperines are generally compact, sturdy snakes, and their length ranges from 11.8 in (30 cm: dwarf puff adder) to 5.9 ft (180 cm: Gaboon adder). Coloration is usually drab, and in the genus Vipera it often includes a dark zigzag pattern or a rhomboid band along the back. Desert species are sand yellow, whereas jungle vipers often have a colorful carpet marking.

Pitvipers exhibit great variety of size, shape, and color, but any pitviper can be recognized easily by the deep, heat-sensitive pits, one on each side of the head, between the eye and the nostril. Color variation within the Crotalinae reflects the diversity of habitats occupied by these snakes: invariably, pitvipers are cryptic in their native haunts. In general, pitvipers are relatively stout, although some arboreal species may be more slender. Tail length varies from quite short in rattlesnakes to relatively long in most arboreal species. The tail is prehensile in species that are adapted fully to an arboreal existence. The longest viperids are pitvipers of the genus Lachesis, some specimens of which are known to reach 11.8 ft (3.6 m).

One of the most well-known and interesting features of pitvipers is the rattle, which is unique to the genera Crotalus and Sistrurus. A neonatal rattlesnake has a keratinized "button" at the tip of its tail; each time the snake sheds, a rattle segment is added. Segments of the rattle fit loosely together, so that a clearly audible sound is produced when the tail is vibrated. Interspecific variation in rattle size has considerable effect on the sound, with large species producing particularly loud and effective warnings. Because most rattlesnakes shed more than once a year and because the ends of rattles tend to break off in wild snakes, the number of rattle segments cannot be used as a direct indication of age.

Sometimes known as night adders, species of Causus are relatively small, terrestrial snakes with a stout body covered by weakly keeled scales. Nine plates cover the top of the head. The pupils are round, and the fangs are relatively short. Despite the short fangs, some species have very long venom glands. The sole living species of Azemiopinae is characterized by smooth scales and nine large plates on top of the head.

The most important distinguishing characteristic in all viperids is the venom apparatus. Their poison fangs have no sign of grooves; they actually have enclosed canals within the fangs that transmit venom out of the body, very much like a hypodermic needle. The two upper jawbones (maxillae), which bear the fangs, are very short. Each maxilla has a special joint that permits this bone, along with the fang anchored firmly within it, to rotate 90°. When the viper closes its mouth, the fangs lay back, tip inward, and are covered by a fold in the mucous membrane. When the mouth is opened, a lifting mechanism is activated, putting the fangs into a vertical position by means of the rod-shaped ectopterygoid bones and the pterygoid. The fangs are then in position to bite and inject venom. The fangs (or, more precisely, the maxillae) are laid back with the same action as when a pocketknife is snapped together. The adaptation of folding back the fangs (referred to as solenoglyphous dentition) permits them to be extremely long, far exceeding the length of those in such snakes as cobras, which bear fangs that are fixed in the down, or vertical, position. The fangs of the giant king cobra are not much longer than those of the rather small adder. The long fangs enable vipers to bite deeply into the tissues and cause the victim to suffer severe necrosis. The fangs fold back into the mouth after they are withdrawn from the victim.

Viper venom contains primarily hematoxic material (i.e., substances injurious to the blood and the blood vessels). Thus, a viper bite typically has a very different effect from a cobra or mamba bite (their venom being primarily neurotoxic, that is, injurious to the nervous system). Viper bites are accompanied by prominent local irritation and symptoms of severe blood poisoning, with burning pain, inflamed swellings, pronounced discoloration, sudden drop in blood pressure, internal bleeding, degeneration of the tissues, and the formation of an abscess. Death ensues because the heart stops, not as the result of respiratory arrest, as in cobra bites. Some vipers, whose venom contains neurotoxic as well as hematoxic substances, are especially dangerous.

Distribution

Viperines, Causus, and Azemiops are found only in the Old World (Europe, Asia, and Africa), but crotalines inhabit both the Eastern and Western Hemispheres. Australia lacks viperids, suggesting that this family evolved after the Australian continent became a separate landmass. The distribution of Causus is restricted to sub-Saharan Africa. Azemiops occurs in southern China, Burma (Myanmar), Laos, and Vietnam. Viperines are distributed in Africa, Europe, and Asia. Crotalines are found in North America, Central America, and South America as well as East Asia and Central Asia. One species (Gloydius halys) enters Europe north of the Caspian Sea.

Habitat

Viperines occur in both tropical and temperate environments, and species have adapted to numerous microhabitats. In temperate regions, species also migrate between different habitats during their active season. The common adder, Vipera berus, moves to meadow habitats with populations of rodents during the summer feeding period, whereas it often occurs on south-facing rocky slopes during the spring and mating periods. Distinct groups of vipers have different connections to special habitats. Macrovipera species occur in dry steppe habitats, whereas the subgenus Montivipera is affiliated with rocky habitats in mountains, the subgenus Pelias with moist grasslands, the subgenus Acridophaga with dry grasslands, and so on. In tropical habitats most species are terrestrial, but Atheris species are arboreal. Of the terrestrial species, some are connected to wet forests (Bitis gabonica and B. nasicornis), and others are savanna inhabitants (B. arietans).

Pitvipers also occupy a wide variety of habitats in temperate and tropical regions. These habitats include temperate forests (Gloydius caliginosus and Agkistrodon contortrix), tropical wet forests (Hypnale hypnale and Bothrocophias hyoprora), tropical deciduous forests (Calloselasma rhodostoma and Porthidium ophryomegas), montane pine-oak forests (Crotalus willardi), cloud forests (Atropoides nummifer), deserts (Crotalus cerastes), and grasslands (Sistrurus catenatus). Several genera of tropical pitvipers (Bothriechis, Bothriopsis, Trimeresurus, and Tropidolaemus) are specialized for an arboreal existence, but most pitviper species are primarily terrestrial. Even terrestrial species occasionally are encountered in trees or shrubs, however. The cottonmouth (Agkistrodon piscivorus) is semiaquatic.

Behavior

Some viperids move over large areas in search of prey during their active season, whereas others are more sedentary. In temperate areas vipers and pitvipers hibernate for several months, and some species (Vipera dinniki, V. darevskii, and Gloydius monticola) at high elevations can hibernate for twothirds of the year. There is no real territoriality, but in some species, such as V. berus, the males actively protect areas around reproductive females during the mating period.

Some vipers inflate their bodies into sausage shapes when they are excited. Almost all vipers also can assume a plate-shaped coiled position as a threat gesture, in which they lift up the neck and hold it in an S shape. Other threat behaviors include loud hissing and rapid forward jerks of the head. Some sand dwellers, such as the saw-scaled vipers, create a particularly impressive sound by rubbing their scales together. Many species of pitvipers vibrate their tails when disturbed, and the evolution of the rattle resulted in amplifiction of the sound produced by this behavior. Several pitviper species (e.g., Agkistrodon piscivorus and Bothriechis schlegelii) give a silent but effective warning by gaping to reveal the bright white lining of the mouth.

Feeding ecology and diet

Viperids feed chiefly on small vertebrates, particularly rats, mice, and lizards, and less often on frogs and birds, paralyzing or killing their prey by biting it. Some of the smallest vipers prefer locusts, and various other vertebrate and invertebrate prey types are known. Many viperids are ambushers and generally lie in wait for their prey, sitting quietly in one spot for long periods of time. Other species may forage actively or employ a combination of active and ambush foraging. The most specialized ambushers may feed quite infrequently. Many species show an ontogenetic shift in prey preference, feeding on small ectotherms (e.g., lizards and frogs) as juveniles and taking endotherms (e.g., rodents) when they are adults. Caudal luring has been observed in juveniles of several viperid species (e.g., Bitis peringueyi and Agkistrodon contortrix), and this behavior is retained in adults of Bothriopsis bilineata. Associated with caudal luring is a distinctive coloration of the tail tip—from black to brown to bright yellow or bright green, depending on the species. Many species withdraw the head immediately after striking prey and subsequently locate the prey by using their Jacobson's organ. Other species, including many arboreal species, hold the prey until it is immobilized and then swallow it. Many vipers are useful for controlling rodent pests.

Reproductive biology

Most viperids have an annual or biennial breeding cycle. A biennial cycle normally is encountered in females in temperate regions, as in Europe, but in some species (e.g., Crotalus horridus) females may reproduce much less frequently. Males always have annual reproduction, which means that reproductive males always outnumber reproductive females in the local population. In Vipera berus the production of sperm takes place during the fall and the following spring, whereas in V. aspis ripe sperm is ready in late fall. In the former species mating is a spring event, triggered by the first molt for the season in males; in the latter species mating can take place during both fall and spring, even if spring mating is most common. In this case the spring molt is not involved in the start of mating activities.

In some genera, such as Vipera, Bitis, Agkistrodon, and Crotalus, males engage in ritualized fights that once were interpreted falsely as mating ceremonies. They lift their heads and approach each other in this vertical position, wrap their bodies around each other, and push with their fore bodies, head to head. In Vipera berus a male hierarchy becomes established, and the dominant male is the first to copulate with a female. By activating a sphincter muscle in the female genital tract, a copulatory plug effect is created temporarily. This lessens the possibility that additional males will fertilize the eggs. In some tropical genera a more lengthy breeding season is reported.

Most viperids are ovoviviparous, bearing live young that hatch from membranous eggs. Pregnancy time, meaning the time from ovulation to birth, is normally about 2.5 months for European vipers. Some viperids (e.g., Lachesis and Deinagkistrodon) lay eggs. The night adders (Causinae) of Africa and the rare Fea's viper (Azemiopinae) of Asia also lay eggs. Incubation has not been noted in any viperine species, nor has any kind of parental care, but egg or neonate attendance has been documented in various pitviper species.

Conservation status

Four viperine species are listed in CITES: Indian Daboia russelii is in Appendix III; Vipera wagneri is in Appendix II, and V. latifii and populations of V. ursinii from regions outside former Soviet territories are in Appendix I. Honduras has seven pitviper species listed in CITES Appendix III: Agkistrodon bilineatus, Atropoides nummifer, Bothriechis schlegelii, Bothrops asper, Crotalus durissus, Porthidium nasutum, and P. ophryomegas. The IUCN lists 19 viperid taxa: 7 as Critically Endangered, 4 as Endangered, 7 as Vulnerable, and 1 as Data Deficient. Habitat destruction is a serious threat to viperid species throughout their range, and several species are threatened by intentional persecution by humans. Many species have extremely limited distributions (e.g., Bothrops insularis and B. alcatraz), leaving them vulnerable to local disturbances. Details of the natural history (including geographic distribution and species limits) of most viperids are not well known, and the number of species listed by CITES and the IUCN probably represents a serious underestimate of the conservation problems affecting this family.

Significance to humans

Bites from viperids are problems at the local level. Snake bites kill 30,000–40,000 people in the world each year. The majority of snakebite cases occur in Asia, with India having the highest number, 10,000–15,000 deaths per year. Vipers such as Daboia russellii and Echis carinatus contribute to a large number of these incidents. Viperids have figured prominently in the legends and religious ceremonies of many cultures. For example, in the first edition of Grzimek's Animal Life Encyclopedia, H.-G. Petzold provided an account of the Hopi snake dance. Certain Christian groups in the southeastern United States "take up serpents" such as Crotalus horridus and Agkistrodon contortrix, as part of their religious ceremonies, grasping the snakes at midbody and dancing with them. The pharmaceutical ancrod (an anticoagulant) is derived from the venom of Calloselasma rhodostoma. In the Old World, viperids are hunted for use in traditional medicine, and in the New World they are persecuted during organized events called rattlesnake roundups. Viperids play critical roles in food webs that affect humans.

Species accounts

List of Species

Fea's viper

Azemiops feae

subfamily

Azemiopinae

taxonomy

Azemiops feae Boulenger, 1888, "Kakhien Hills (Kachin Hills)" Myanmar (Burma).

other common names

German: Fea-Vipern.

physical characteristics

Fea's viper has no facial pit between the nostrils and eyes. The head is white in color and covered by large symmetrical shields. The body and tail are black with about 18 short transverse orange to yellow bands laterally along each side.

distribution

Fea's viper occurs in central and southern China from western Yunnan and Sichuan east to Zhejiang and south to Guangxi. It also inhabits northern Burma and northern Vietnam (Tonkin).

habitat

Fea's viper inhabits bamboo and tree fern forest alternating with open-light sites. It prefers ground covered with soft layers of deciduous leaves, decomposed trunks of tree ferns, and vigorous outcrops of the karst formation, permanently permeated by numerous open and subterranean streams.

behavior

Fea's viper moves very slowly and shows no aggressive behavior.

feeding ecology and diet

A shrew was found in the stomach of one specimen, and in captivity mice and lizards have been accepted.

reproductive biology

Nikolai Orlov describes the mating behavior as similar to that of other vipers. The male courts the female by twitching the head along the female's body. The short copulation lasts about 10 minutes. The species is oviparous. Little else is known about the reproductive biology.

conservation status

Although not listed by the IUCN, this is a very rare snake.

significance to humans

There are no conflicts with humans.

Rhombic night adder

Causus rhombeatus

subfamily

Causinae

taxonomy

Causus rhombeatus Lichtenstein, 1823, type locality not specified.

other common names

English: Common night adder, demon adder; French: Vipére nocturne, vipère-démon; German: Krötenotter, Pfeilotter, Nachtadder, Nachtotter.

physical characteristics

The night adder is a rather small, stout viper with a distinct rounded head covered by nine larger shields. The pupil is round. The dorsal scales are weakly keeled, and the body is cylindrical. The tail is short. The maximum size of this viper is less than 3.3 ft (1 m), but the average size is only about 11.8–23.6 in (30–60 cm). The normal color pattern is brownish gray with shades of green. Along the back there is a series of about 20–30 dark, light-edged rhombic blotches. On the head there is a characteristic arrow-shaped pattern. The dorsal pattern can vary locally, and occasionally there are patternless specimens.

distribution

The rhombic night adder is distributed widely in southern and eastern Africa and reaches the Cape of Good Hope in the south. It also has a scattered distribution in Zimbabwe, Angola, Zambia, Congo, Kenya, Nigeria, Ethiopia, and Sudan.

habitat

It occurs in open habitats, such as savanna, grasslands, forest edges, and swamps.

behavior

The viper hisses ferociously when disturbed.

feeding ecology and diet

Frogs and toads are the most important prey items.

reproductive biology

The species is oviparous and can lay from seven to 26 eggs.

conservation status

Not threatened.

significance to humans

Very few bites are recorded.

Cottonmouth

Agkistrodon piscivorus

subfamily

Crotalinae

taxonomy

Agkistrodon piscivorus Lacépède 1789 Carolina, later restricted to the vicinity of Charleston, South Carolina. Three subspecies are recognized.

other common names

English: Water moccasin; French: Mocassin d'eau; German: Wassermokassinschlange, Wassermokassinotter.

physical characteristics

The cottonmouth is a large, robust snake, occasionally exceeding 5.9 ft (1.8 m) in length and 10 lb (4.6 kg) in weight. One well-fed captive specimen reached a weight of about 23 lb (10.4 kg). In older adults, the dorsum typically is a uniform dark brown, black, or olive. Younger specimens have a lighter ground color with dark brown or reddish brown bands. Juveniles have a bright yellow or greenish tail tip. The loreal scale is absent (fused to the upper preocular scale). For this species, 23–27 (25 in most individuals) midbody scale rows have been recorded, along with 6–9 (8 in most individuals) supralabial scales, 128–145 ventral scales, and 36–53 subcaudal scales.

distribution

The cottonmouth inhabits the southeastern United States from southeastern Virginia south to Florida and west to central Texas and Oklahoma.

habitat

This snake inhabits swamps, streams, rivers, ponds, lakes, coastal marshes, rice fields, and several offshore islands. Occasionally it is found away from water.

behavior

Cottonmouths are semiaquatic and can be found coiled in the open during the day or night. The name cottonmouth describes the bright white lining of the mouth, which is shown as a warning to creatures that approach too closely. It may be active during any month in the southern part of the range, but more northern populations hibernate. Most individuals are not aggressive, but numerous exceptions are known. This dangerous snake should not be handled.

feeding ecology and diet

The cottonmouth frequently forages by ambush, but it also may search actively for prey or feed on carrion. An interesting population on Seahorse Key, Florida, relies heavily on dead fish and young birds that drop from the nests of cormorants, herons, and egrets. Known prey include fish, amphibians, reptiles (among them, small alligators and turtles and even other cottonmouths), birds and their eggs, mammals, snails, insects, and crayfish. Juveniles attract prey by undulating their brightly colored tail tips.

reproductive biology

This species gives live birth to 1–16 young, usually in August or September. Male combat has been documented.

conservation status

The cottonmouth is still an abundant snake in many parts of its range, although local populations are threatened frequently or extirpated by habitat alteration (e.g., draining of wetlands, channeling of streams, and building of dams).

significance to humans

The cottonmouth is a dangerously venomous snake; bites can cause severe trauma and even death. In the past, this species has been killed systematically through organized snake hunts.

Yellow-blotched palm-pitviper

Bothriechis aurifer

subfamily

Crotalinae

taxonomy

Bothriechis aurifer Salvin, 1860, Cobá, Alta Verapaz, Guatemala.

other common names

Spanish: Cantil loro, cantil verde.

physical characteristics

The yellow-blotched palm-pitviper is a small, relatively slender snake with a prehensile tail. Specimens longer than 3.3 ft (1 m) are known, but the length of most adults is less than 2.3 ft (70 cm). The dorsum is green with small yellow blotches with black borders. A black postocular stripe is almost always present. A few specimens may be uniformly green dorsally. For this species, 18–21 midbody (most individuals have 19) scale rows have been recorded, along with 8–12 supralabial scales, 148–167 ventral scales, and 48–64 subcaudal scales.

distribution

The species occurs in southern Mexico and Guatemala.

habitat

The yellow-blotched palm-pitviper inhabits cloud forest and pine-oak forest, usually at elevations of 3,940–7,550 ft (1,200–2,300 m).

behavior

The species is arboreal and diurnal.

feeding ecology and diet

On many occasions, the yellow-blotched palm-pitviper has been observed actively foraging in terrestrial bromeliads. Known prey include treefrogs and small mammals.

reproductive biology

It gives live birth to five to eight young.

conservation status

This species is not listed by the IUCN. However, extensive destruction of cloud forest throughout the range of this snake continues to extirpate local populations and threatens the entire species.

significance to humans

This is a dangerously venomous snake; at least one human fatality has resulted from the bite of this species.

Patagonian lancehead

Bothrops ammodytoides

subfamily

Crotalinae

taxonomy

Bothrops ammodytoides Leybold, 1873, Mendoza Province, northern Argentina.

other common names

German: Argentinische Jararaca; Spanish: Cenicienta.

physical characteristics

Adults range from 1.5 ft (45 cm) to 3.3 ft (1 m) in total length. The dorsal ground color is light brown or gray with dark brown blotches. The snout is elevated. Eight to 11 supralabial, 147–160 ventral, 30–41 subcaudal, and 23–25 midbody scale rows have been recorded for this species.

distribution

The species occurs in Argentina, from sea level to 6,560 ft (2,000 m).

habitat

It inhabits temperate to subtropical savannas and steppes.

behavior

The species is terrestrial. In parts of its range, the Patagonian lancehead may use the tunnels of the chinchillid mammal Lagostomus maximus. The species has been characterized as an irritable snake. It is inactive during the austral winter.

feeding ecology and diet

It feeds primarily on lizards.

reproductive biology

The Patagonian lancehead gives live birth, but little else is known.

conservation status

Not threatened.

significance to humans

This snake is dangerously venomous.

Timber rattlesnake

Crotalus horridus

subfamily

Crotalinae

taxonomy

Crotalus horridus Linnaeus, 1758, "America," later restricted to the vicinity of New York City, United States. Two subspecies have been recognized, but this taxonomy has been questioned.

other common names

English: Canebrake (for southern populations); French: Crotale des bois; German: Waldklapperschlange.

physical characteristics

This large, heavy-bodied snake reaches almost 5 ft (1.5 m) in total length; examples exceeding 6 ft (1.8 m) are known. The ground color of the dorsum may be yellow, gray, tan, or brown to black with dark chevron-shaped blotches. An orange to rust-colored vertebral stripe is present in many individuals; the stripe is especially prominent in snakes from the southern and western parts of the range. The tail is black with a large rattle at the tip. A postocular stripe may be present or absent. Ten to 17 supralabial, 158–183 ventral, 13–30 subcaudal, and 21–26 midbody scale rows have been recorded for this species.

distribution

The snake occurs in the eastern United States from New Hampshire, Vermont, and New York south to Florida and west to Minnesota, Nebraska, Kansas, Oklahoma, and Texas.

habitat

Forested hillsides with rock outcrops are preferred den sites for northern populations of timber rattlesnakes, but males and nongravid females move into more densely canopied forest during the active season. Southern populations occur in hardwood forests of bottomland floodplains, wet pine flat woods, upland woodlands, and canebrakes (thickets of cane).

behavior

Communal dens are used for hibernation in the north, but in the south, snakes hibernate individually or in very small groups. During the active season, some individuals travel great distances from the den site; a migration of more than 4.3 mi (7 km) was documented for one male in a New York population.

feeding ecology and diet

Timber rattlesnakes forage mainly by ambush and may consume only 6–20 meals per year. They feed mainly on mammals but also take birds, lizards, snakes, anurans, and insects.

reproductive biology

This species gives live birth to three to 19 (usually six to 10) young. Females may give birth every other year, every third year, or every fourth year; even longer intervals have been reported. Females do not produce their first litters until they have reached an age of four to nine years. Male combat has been observed (usually in April or May), but reports from Louisiana indicate that combat there occurs in the fall.

conservation status

This species is not listed by the IUCN. However, as of August 2002 the species is listed as threatened or endangered by eight U.S. states, and it is believed to be extirpated from Maine and Rhode Island and from Ontario, Canada. With its low reproductive rate and typically long-lived adults, this species is extremely vulnerable to human disturbance.

significance to humans

The bites of this dangerously venomous snake are potentially life-threatening. In Landscape with Reptile, Thomas Palmer recounts the long history of interactions between humans and timber rattlesnakes. There are elements of hope in this story but also much to regret about the toll that humans have taken on this beautiful and unusual species.

Hundred-pace pitviper

Deinagkistrodon acutus

subfamily

Crotalinae

taxonomy

Deinagkistrodon acutus Günther, 1888, Wusueh, Hupeh Province, China. No subspecies are recognized.

other common names

English: Long-nosed pitviper, sharp-nosed pitviper; German: Chinesische Nasenotter.

physical characteristics

This is a large, stout-bodied pitviper, sometimes exceeding 5 ft (1.5 m) in total length. Distinctive features of this species include a protuberant snout and tuberculate keels on the dorsal scales. Nine symmetrical plates cover the crown, although some

fragmentation of these plates is evident in many specimens. Typically, there are seven supralabial and 21 middorsal scale rows and 157–174 ventral and 51–61 subcaudal scale rows. The top of the head is dark brown with a thin, darker postocular stripe. The dorsal ground color is pale gray or brownish gray with dark crossbands that are triangular in lateral view.

distribution

The species occurs in southeastern China, Taiwan, and northern Vietnam.

habitat

It inhabits forested hills and mountains at elevations of 330–4,920 ft (100–1,500 m). It often is found near streams and in rocky areas.

behavior

The hundred-pace pitviper often is found coiled in the open during the day but also is frequently active at night. It usually raises the head, vibrates the tail, and then strikes if disturbed. In northern Fukien Province, China, these snakes are known to hibernate from late December to early March, but probably they do not hibernate in some warmer parts of the range.

feeding ecology and diet

This snake is known to prey on amphibians, reptiles, birds, and mammals; rodents and anurans are the most common prey.

reproductive biology

Courtship has been observed from March through May and also September through December. The female lays five to 32 eggs between June and early September. Eggs, which are attended by the female, hatch in approximately 20–30 days.

conservation status

This species is not listed by the IUCN. However, with the widespread collection of these snakes for the traditional medicine trade, their status warrants investigation.

significance to humans

In their classic monograph on the Agkistrodon complex, Howard Gloyd and Roger Conant summarize the extensive use of the hundred-pace pitviper by various Asian cultures. According to the legends and myths of the Paiwan, a tribe indigenous to Taiwan, their first leaders came from the eggs of the hundred-pace pitviper, and the snake features prominently in their art. It is exploited heavily for the traditional medicine trade; raw gall-bladders of these snakes are especially prized, but the skin, flesh, eyes, and bones also are used. Snake soup sometimes is prepared from this species; alternatively, entire snakes are preserved in wine, and the wine is used as medicine. Although this is a dangerously venomous snake, its most common English name, hundred-pacer (one can walk only 100 paces before dying), exaggerates the danger; with prompt and proper treatment, bites are rarely life-threatening.

Tibetan pitviper

Gloydius strauchi

subfamily

Crotalinae

taxonomy

Gloydius strauchi Bedriaga, 1912, Tungngolo, Szechwan Province, China (as restricted by Pope in his 1935 work on the reptiles of China). No subspecies are recognized.

other common names

None known.

physical characteristics

This is a relatively small snake that typically does not exceed 19.7–21.7 in (500–550 mm) in total length. The largest male recorded was 20 in (510 mm) in total length, and the largest female was 21.5 in (547 mm) in total length. The ground color of the dorsum may be brown or greenish brown with four dark longitudinal stripes. These stripes are usually incomplete and curved such that individuals may appear spotted or exhibit a zigzag pattern on parts of the dorsum. A dark postocular stripe is present, and there are dark markings on the top of the head. Some adults are uniformly dark in color. The crown has nine symmetrical plates. Most specimens have seven supralabial and 21 middorsal scale rows. Ventral scales range from 145 to 175, and subcaudal scales range from 34 to 44.

distribution

The Tibetan pitviper occurs in southern China in Szechuan and Tsinghai Provinces.

habitat

The species inhabits the Tibetan Plateau at elevations between 9,470 ft (2,886 m) and 14,000 ft (4,267 m).

behavior

Little is known about this terrestrial species, but it must hibernate for extended periods, owing to the climatic conditions within its range.

feeding ecology and diet

One specimen was reported to contain a young pika (Lagomys).

reproductive biology

The Tibetan pitviper is thought to give live birth; seven partially developed embryos were found in one specimen.

conservation status

Not listed by the IUCN. Additional study of this snake is needed; at present too little is known of its biology to evaluate its status.

significance to humans

There are no records of human envenomation, nor is this species known to be exploited by humans to any appreciable degree.

Sri Lankan hump-nosed pitviper

Hypnale nepa

subfamily

Crotalinae

taxonomy

Hypnale nepa Laurenti, 1768, Sri Lanka. No subspecies are recognized.

other common names

None known.

physical characteristics

The Sri Lankan hump-nosed pitviper is a small snake. Adults usually are 11.8–13.8 in (300–350 mm) in total length, but slightly larger specimens are known. The ground color of the dorsum is light or dark brown with 17–26 pairs of small dark brown blotches. In some individuals, the thin, dark postocular stripe is bordered dorsally by a thin white line. The snout is upturned and bears a small hump covered by tiny scales. As in other members of the genus, the five posterior head plates are mainly intact, but the anterior plates (internasals and prefrontals) are replaced by numerous small scales. Seven to nine supralabial, 124–142 ventral, 33–41 subcaudal, and 17 midbody scale rows have been recorded for this species.

distribution

The species occurs in southwestern Sri Lanka.

habitat

Their habitat is wet forest from near sea level to 6,000 ft (1,830 m). Additional study is needed to assess the lower elevation limits of this species; it is possible that specimens of Hypnale nepa and H. walli have been confused in some reports.

behavior

The Sri Lankan hump-nosed pitviper is terrestrial and mainly nocturnal, but it sometimes is encountered during the day. It is not aggressive and generally does not attempt to bite unless it is molested.

feeding ecology and diet

Known prey include lizards, snakes, frogs, and reptile eggs.

reproductive biology

Little is known about the reproduction of this species. It gives birth to live young. Gravid females containing four to six immature eggs have been reported.

conservation status

This species is not listed by the IUCN. However, with its limited distribution and preference for areas of dense forest, the Sri Lankan hump-nosed pitviper is vulnerable to habitat destruction. Fortunately, there are national parks and forest reserves within its range.

significance to humans

This is a dangerously venomous snake, but reports of contact with humans are few.

Black-headed bushmaster

Lachesis melanocephala

subfamily

Crotalinae

taxonomy

Lachesis melanocephala Solórzano and Cerdas, 1986, 5.6 mi (9 km) north of Ciudad Neily, Puntarenas Province, Costa Rica.

other common names

German: Schwarzkopf-Buschmeister; Spanish: Cascabel muda, matabuey, plato y negro.

physical characteristics

This extremely large snake commonly reaches 6.6 ft (2 m), and specimens of 7.5–7.9 ft (2.3–2.4 m) have been documented. The snout is distinctively rounded. A vertebral ridge is present; and the dorsal scales bear tubercular keels such that the body appears rough. The dorsal ground color is yellow, tan, or brown with black diamond-shaped blotches. The top of the head is black. Seven to nine supralabial, 209–222 ventral, 35–54 subcaudal, and 36–41 midbody scale rows have been recorded for this species.

distribution

The species occurs in southwestern Costa Rica and possibly adjacent parts of Panama.

habitat

It inhabits lowland wet and moist forest and premontane wet forest.

behavior

The black-headed bushmaster is terrestrial. Some use rodent or armadillo burrows as refuges. It may vibrate the tail when disturbed.

feeding ecology and diet

This species forages by ambush. Rodents and marsupials are probably the main prey.

reproductive biology

Females may lay up to 16 eggs; two clutches laid in captivity included nine and 13 eggs, respectively. Females remain with the eggs until they hatch.

conservation status

Although not listed by the IUCN, this species is relatively uncommon and has a restricted distribution.

significance to humans

The black-headed bushmaster is dangerously venomous; any bite should be considered life-threatening. Other species of bushmaster (e.g., Lachesis muta) are used as food. Bushmasters, in general, feature prominently in forest lore, probably owing mainly to their formidable size and lethal venom.

Green bush viper

Atheris squamigera

subfamily

Viperinae

taxonomy

Atheris squamigera Hallowell, 1856, "near the river Gabon, Guinea" (Gabon). Two subspecies are recognized.

other common names

English: Common bush viper, leaf viper, variable bush viper; French: Vipère d'arbre; German: Blattgrüne Buschviper.

physical characteristics

The green bush viper is a species that grows up to 31 in (78 cm) in size, with the females larger than the males. The body is covered with strongly keeled scales. The tail is comparatively long and prehensile. The color varies, with yellow, reddish, and gray specimens. The majority of individuals are greenish.

distribution

The species occurs through the tropical belt of western and central Africa, from Ghana in the west to Uganda and western Kenya in the east. Southward it is distributed down to northern Angola.

habitat

This is a rainforest species, often preferring low, thick, flowering bushes.

behavior

During the daytime it can be found up in the vegetation, while in some investigated populations it moves down toward the ground at night to prey on ground rodents.

feeding ecology and diet

Rodents are the main prey items for adult bush vipers.

reproductive biology

Mating takes place in October, and the live young are born during March and April. The clutch size is about seven to nine young.

conservation status

Not threatened.

significance to humans

Few bites are recorded, but fatal cases are known.

Gaboon adder

Bitis gabonica

subfamily

Viperinae

taxonomy

Bitis gabonica Duméril Bibron, and Duméril, 1854, "Gabon." Two subspecies are recognized.

other common names

English: Gaboon viper; French: Vipère du Gabon; German: Gabunviper, Gabunotter.

physical characteristics

This species reaches an average size of about 4 ft (120 cm), but it can grow to more than 6.6 ft (2 m). The fangs can be longer than 2 in (50 mm), and the head and body are very broad. The West African subspecies, B. g. rhinoceros, bears a pair of horn-like knobs on the top of the snout. The Gaboon adder has a geometric pattern with rich pastel, brown and whitish colors.

distribution

The nominate subspecies of the Gaboon adder is distributed in central, eastern and southern Africa. The western subspecies, B. g. rhinoceros, occurs in West Africa.

habitat

This is a tropical forest species, which is well camouflaged on the forest floor.

behavior

The Gaboon adder is a placid species that very rarely strikes. The protection behavior is a loud hissing sound.

feeding ecology and diet

Like most vipers, they forage from an ambush position on the forest floor. The prey consists mostly of rodents, even when larger prey, such as mongoose, hares, and monkeys, can be taken.

reproductive biology

This species gives birth to live young. Clutch sizes can be very large, as many as 60 young in a single clutch. Normally, the clutch size is smaller (16–30 in the western subspecies).

conservation status

Not threatened. The species is considered very common in prime forest habitats.

significance to humans

Bites are very rare, as the species is very docile and lives in the rainforest. When bites occur, however, fatalities are common.

Horned viper

Cerastes cerastes

subfamily

Viperinae

taxonomy

Cerastes cerastes Linnaeus, 1758, "Egypt." Two subspecies are recognized.

other common names

English: Desert horned viper, Saharan horned viper; French: Vipère à cornes; German: Hornviper.

physical characteristics

The horned viper is rather short and stout in body shape, and the tail is short. The head is triangular and covered with small scales. Many specimens have a raised horn over each eye. Hornless specimens have a raised brow ridge. The horn is made up of a single elongated scale. The neck is thin, and the body is covered with pronouncedly keeled scales, in 25–35 rows. The size typically is between 11.8 in (30 cm) and 23.6 in (60 cm), but occasionally specimens can grow to 2.8 ft (85 cm). The ground color is mostly grayish, yellowish, or reddish with a series of rectangular brown blotches along the back.

distribution

The horned viper occurs in northern Africa in sandy habitats. It also occurs in eastern Sinai.

habitat

To a large extent, this is a sand-dwelling species, but it often may live in habitats mixed with rocks and stones. Occasionally, it occurs in ground with more clay, typically mixed with some sandy soils.

behavior

During the daytime this nocturnal species hides under rocks or in rodent burrows, and it will even dig down into the sand.

feeding ecology and diet

The prey consist of rodents, lizards, and birds.

reproductive biology

This viper is oviparous and can produce between 10 and 23 eggs.

conservation status

The species has a rather wide distribution and is not threatened.

significance to humans

Bites do occur, but the species is not thought to be particularly dangerous.

Russel's viper

Daboia russelii

subfamily

Viperinae

taxonomy

Daboia russelii Shaw and Nodder, 1797, India (Coromandel Coast). Two subspecies are recognized.

other common names

English: Chain viper; French: Vipère de Russel; German: Kettenviper.

physical characteristics

This species is characterized by a pattern of three longitudinal rows of reddish brown, black-edged, oval or circular spots on a mostly brownish yellow or brownish gray ground color.

distribution

Russel's viper occurs in Southeast Asia, from India, Pakistan, and Sri Lanka to Taiwan in the east and Java, Komodos, and Flores in the south. The distribution is not continuous within this large area.

habitat

The species prefers plains, savannas, or hills, and it is encountered regularly in agricultural areas.

behavior

It is mainly a nocturnal snake; if encountered during the daytime, it is rather sluggish and, unless attacked, is not aggressive.

feeding ecology and diet

It mainly preys on rodents but also takes frogs, birds, and lizards.

reproductive biology

This large ovoviviparous species can give birth to 20–63 live young in each clutch.

conservation status

This species is not listed by the IUCN. However, some populations of Russel's viper are endangered, primarily because of collection for leather production or as food. The Indian populations are listed in Appendix III of CITES.

significance to humans

Russel's viper is the most dangerous viper in Southeast Asia and is of great medical importance. This species is responsible for a majority of cases of snakebite injury and death within its range, especially in densely populated areas of the Indian subcontinent. In Sri Lanka and Burma (Myanmar), approximately 2,000 bites and 900 deaths per year are attributed to Russel's viper.

Saw-scaled viper

Echis carinatus

subfamily

Viperinae

taxonomy

Echis carinatus Schneider, 1801, "Arni," near Madras, India. Four subspecies are recognized.

other common names

English: Carpet viper; French: Échide carénée; German: Sandrasselotter.

physical characteristics

The saw-scaled viper is a comparatively small snake, 15–23.6 in (38–60 cm) in length, with an oval head and strongly keeled scales in 27–36 rows around the body. It produces its characteristic sound by coiling its body in parallel loops and rubbing the body sides, with its serrated lateral body scales, together.

distribution

It occurs as several subspecies from India and Sri Lanka in the east to the United Arab Emirates and Oman in the west. In northern Africa and other parts of Asia there are numerous similar species that until recently were considered subspecies of E. carinatus but which today are separated at the species level.

habitat

The saw-scaled viper prefers dry, often rocky habitats but also may occur on dry, grassy slopes or even sandy habitats.

behavior

This species is a good sidewinder and can move quickly. When threatened, it coils up in a horseshoe fashion and rubs the sides of its body together in opposite directions while producing a sharp sizzling sound. This species is mostly nocturnal.

feeding ecology and diet

This viper forages broadly and can eat many different kinds of small animals, such as centipedes, scorpions, birds, rodents, frogs, lizards, and even other snakes.

reproductive biology

The saw-scaled viper is oviparous and can produce up to 20 eggs.

conservation status

Not threatened.

significance to humans

Saw-scaled vipers are very aggressive and quick to strike. They produce highly virulent hematoxic venom. In addition, they are often abundant in heavily populated regions, which makes them some of the most dangerous snakes in the world.

Levantine viper

Macrovipera lebetina

subfamily

Viperinae

taxonomy

Macrovipera lebetina Linnaeus, 1758, Cyprus. Five subspecies are recognized.

other common names

English: Blunt-nosed viper; French: Vipère du Levant; German: Levante-Otter.

physical characteristics

This is a large viper with a head covered with small scales. In some eastern subspecies the supraocular scale can be larger but almost always is semidivided. All body scales are keeled. The color typically is grayish with numerous dark brown or dark gray crossbands, which may be more or less indistinct. The maximum size of this species is 7 ft (214 cm).

distribution

Numerous subspecies occur in dry habitats in western Asia from Cyprus and central Turkey to Pakistan and Kashmir. One subspecies (M. l. transmediterranea) is distributed in North Africa (Tunisia and Algeria).

habitat

The species occurs in several kinds of dry habitats, such clay steppes, rocky mountain slopes, grass meadows, and dry deciduous forests. It often is seen near natural water streams or human-made channels. It is well adapted to agriculture areas.

behavior

The Levantine viper is mainly nocturnal and is largely responsible for snake bites in the Near East and Middle East, which occur when people walk around at night. When it is disturbed, it typically makes a loud hissing sound.

feeding ecology and diet

It is an opportunistic species and feeds on various kinds of rodents, birds, and lizards.

reproductive biology

Like all Macrovipera, the Levantine viper is oviparous, but the hatching time varies between different populations and areas. In some cases the embryos are rather well developed when the eggs are deposited. A single clutch can consist of up to 35 eggs.

conservation status

Not threatened. The species is locally abundant within its range.

significance to humans

The Levantine viper generally is considered dangerously venomous. Bites have been fatal to humans, horses, cows, and camels.

Common adder

Vipera berus

subfamily

Viperinae

taxonomy

Vipera berus Linnaeus, 1758, Uppsala, Sweden (terra typica restricta). Three subspecies are recognized.

other common names

French: Vipér peliad; German: Kreuzotter.

physical characteristics

Males are 21.7–25.6 in (55–65 cm), and females are 23.6–27.6 in (60–70 cm) in length. This is a medium-sized viper with sexual dimorphism. Males have a gray ground color with a black dorsal zigzag band; females are brown or reddish brown, with a dark brown zigzag band along the back. Locally, up to 50% of the snakes in the population are totally melanistic.

distribution

The species is distributed in Europe from the Russian Kola Peninsula in the north to northern Italy and Greece in the south. Eastward it is distributed through Asia to the island of Sakhalin north of Japan and to North Korea.

habitat

The species prefers mesic habitats with meadows and moorland. It can be found at the edges of forests.

behavior

Males defend a small territory around reproductive females during a few spring weeks (May) and engage in pronounced combat behavior during the mating period.

feeding ecology and diet

Small rodents and especially voles (Microtus) are the main food item for adults. Occasionally birds, frogs, and lizards are eaten. Juvenile adders take frogs and lizards as prey.

reproductive biology

Females usually reproduce every second year, but occasionally less often. Males reproduce every year. The mating period is in May, and the young are born (ovoviviparity) in August or September. The clutch size is, on average, 10 young, but it can vary between two and 18 young.

conservation status

Although not listed by the IUCN, this species has a fragmented distribution in central Europe and is locally endangered. It is more abundant in the northern parts of its distribution (Scandinavia and Russia). It is protected in most European countries.

significance to humans

The common adder causes numerous bites throughout its range every year, but very few are fatal.

Resources

Books

Campbell, Jonathan A., and Edmund D. Brodie Jr. Biology of the Pitvipers. Tyler, TX: Selva, 1992.

Campbell, Jonathan A., and William W. Lamar. The Venomous Reptiles of Latin America. Ithaca, NY: Cornell University Press, 1989.

——. The Venomous Reptiles of the Western Hemisphere. Ithaca, NY: Cornell University Press, 2003.

Ernst, Carl H. Venomous Reptiles of North America. Washington, DC: Smithsonian Institution Press, 1992.

Gloyd, Howard K., and Roger Conant. Snakes of the Agkistrodon Complex: A Monographic Review. Vol. 6, Contributions to Herpetology. Oxford, OH: Society for the Study of Amphibians and Reptiles, 1990.

Jena, I. Snakes of Medical Importance and Snake-bite Treatment. New Delhi: Ashish Publishing House, 1985.

Mallow, D., D. Ludwig, and G. Nilson, True Vipers: Natural History and Toxinology of Old World Vipers. Melbourne, FL: Krieger Publishing Company, 2003.

Nilson, G., and C. Andrén. "Evolution, Systematics and Biogeography of Palearctic Vipers." In Venomous Snakes: Ecology, Evolution and Snakebite, edited by R. S. Thorpe, W. Wüster, and A. Malhotra. Symposia of the Zoological Society of London. London: Oxford University Press, 1997.

Palmer, T. Landscape with Reptile: Rattlesnakes in an Urban World. New York: Ticknor and Fields, 1992.

Schuett, Gordon W., Mats Höggren, Michael E. Douglas, and Harry W. Greene, eds. Biology of the Vipers. Eagle Mountain, UT: Eagle Mountain Publishing, 2002.

Spawls S., and B. Branch. The Dangerous Snakes of Africa. Sanibel Island, FL: Ralph Curtis Books, 1995.

Periodicals

Lenk P., S. Kalyabina, M. Wink, and U. Joger. "Evolutionary Relatonships Among the True Vipers (Viperinae) Inferred from Mitochondrial DNA Sequences." Molecular Phylogenetics and Evolution 19, no. 1 (2001): 94–104.

Parkinson, C. L. "Molecular Systematics and Biogeographical History of Pitvipers as Determined by Mitochondrial Ribosomal DNA Sequences." Copeia (1999): 576–586.

Parkinson, C. L., K. M. Zamudio, and H. W. Greene. "Phylogeography of the Pitviper Clade Agkistrodon: Historical Ecology, Species Status, and Conservation of Cantils." Molecular Ecology 9 (2000): 411–420.

Warrell D. "Tropical Snakebite: Clinical Studies in South East Asia." Toxicon 23 (1985): 543.

Göran Nilson, PhD

Ronald L. Gutberlet, Jr., PhD