VIPERS AND PITVIPERS: Viperidae

PHYSICAL CHARACTERISTICS

Vipers and pitvipers are mainly known for the pair of short hollow fangs that usually lie flat in the upper jaw but swing down when the snake opens its mouth to inject its venom. The members of this family are typically rather thick snakes with large triangular-shaped heads, usually catlike eye pupils, and short tails. The tail in a snake is the part of the body behind the vent, a slitlike opening on the belly side of the animal. Those snakes that spend much of their time climbing among shrubs and trees have longer tails. Some vipers and pitvipers have zigzag, diamond-shaped, or other patterns on their backs, but for the most part, vipers and pitvipers have no showy colors and instead simply blend into the background, which often makes them difficult to spot.

The pitvipers are unusual because each has a rattle on the end of the tail and a small but deep pit on either side of the face. The rattle is made of little segments of fingernail-like material that make a noise when they knock against one another. The snake gets a new segment every time it sheds, but the oldest segments frequently fall off. The pits on the snake's face are sensitive to temperature, so the pitvipers have infrared (IN-fruh-red) vision, which is the ability to detect, or to "see," heat.

Vipers and pitvipers come in different sizes. The smallest member of the family is the dwarf puff adder, which grows to about 12 inches (30.5 centimeters). The largest are some of the pitvipers, which reach 11.8 feet (3.6 meters) in length.

GEOGRAPHIC RANGE

Vipers and pitvipers are found in North, Central, and South America and in Africa, Europe, and Asia.

HABITAT

Most members of this family live on land, but some, such as the cottonmouth, spend a good part of their time in the water. Vipers and pitvipers make their homes in warm tropical climates and in cooler temperate climates that have distinct seasons, including cold winters. Temperate species often move from one habitat to another during the spring, summer, and fall and then hibernate through the winter. For example, North America's eastern massasauga rattlesnake spends the early spring near wetlands, moves into drier nearby fields for the hot summer months, and hibernates back near the water in underground burrows made by crayfish or small mammals. During hibernation (high-bur-NAY-shun), the animal enters a state of deep sleep that helps it to survive the frigid weather.

DIET

Vipers and pitvipers eat mice, rats, and lizards, but they will also feed on birds, frogs, and other animals. A few of the smallest species eat locusts, a type of grasshopper.

Vipers and pitvipers are predators (PREH-dih-ters) and use their venom when hunting prey or sometimes when defending themselves. The venom attacks the blood system of the prey, producing burning pain and other symptoms, and later stopping the heart. A few vipers and pitvipers have venom that also attacks the nervous system. Some species slowly slither along looking for prey animals, but others rely on their camouflage-like colors to hide them until an unsuspecting animal happens by. In either case, the snake lashes out at the prey animal with great speed, opening its mouth to swing down its fangs and biting the animal to inject the venom—all in the blink of an eye. The prey never even sees the snake until it is too late.

BEHAVIOR AND REPRODUCTION

The defense behaviors of the vipers and pitvipers are perhaps their best-known feature. The snakes coil up into a flat spiral with the head curved up from the middle of the coil. Some also hiss, jerk forward with the head, rattle the tail, or blow up the body, which makes the snake look larger. Each of the behaviors may be enough to scare off a predator. Many of the warmer climate species remain active all year long, but the temperate species may hibernate for many weeks. Those living high up in the mountains and other places with especially cold winters typically hibernate for several, sometimes up to eight, months a year.

Males mate every year in the spring or fall, sometimes wrestling with other males over the chance to mate with a female. Females, especially those in colder climates, often skip a year or more between matings. The females of most species produce eggs, but these hatch inside her body so that she gives birth to baby snakes. A few species, such as the night adders, lay eggs instead. Recent research suggests that some mothers may linger around the young for a few days, possibly providing some protection against predators that may hunt them for food.

VIPERS, PITVIPERS, AND PEOPLE

While viper and pitviper bites of humans are quite rare, they do occur often enough and cause enough deaths to be a concern in some areas. For this reason, people often kill vipers and pitvipers, along with any other snakes that remotely resemble them. In addition, people hunt and kill these snakes to use in medicines.

FIGHTING SNAKE BITES

Although many snakes are harmless to humans, some produce venom and can be quite deadly. People who have been bitten by a venomous snake often receive antivenin (an-tee-VEH-nuhn) to stop the venom from doing its damage. To make antivenin, a snake handler forces a venomous snake to bite and release its venom into a container. When enough is collected, the venom is injected into a horse. The horse's body, which is much larger than a human's, fights off the venom by making special proteins, called antibodies. Laboratory technicians collect these antibodies to make antivenin. Usually, one type of antivenin is good at attacking only one type of venom, so a medical doctor tries to learn exactly what species of snake bit the patient before giving the antidote or cure.

CONSERVATION STATUS

According to the World Conservation Union (IUCN), seven species are Critically Endangered; four species are Endangered; seven species are Vulnerable, and one species is listed as Data Deficient. The Critically Endangered species face an extremely high risk of extinction in the wild, while the Endangered species face a very high risk, and the Vulnerable face a high risk. Scientists have too little information on those noted as Data Deficient to make a judgment about the threat of extinction. The U.S. Fish and Wildlife Service lists one U.S. and one foreign species as Threatened or likely to become endangered in the foreseeable future, and one foreign species as Endangered or in danger of extinction throughout all or a significant portion of its range. Overall, the loss of habitat and outright killing of the snakes by humans are the greatest risks the snakes face.

HORNED VIPER (Cerastes cerastes): SPECIES ACCOUNTS

Physical characteristics: A thick snake with a short tail, the horned viper has a triangle-shaped head and a long scale over each eye that pokes up like a horn. Some individuals have a ridge over their eyes instead of the two tall horns. They have brown blotches down a gray, yellow- or red-tinged back, and the back and head scales have ridges, or keels. Adults are quite small, usually growing to just 11.8 to 23.6 inches (30 to 60 centimeters), although a few reach 2.8 feet (85 centimeters).

Geographic range: Horned vipers are found in northern Africa and the eastern Sinai.

Habitat: This species lives mostly in sandy areas, sometimes marked with stones and rocks.

Diet: They eat other animals of sandy habitats. These may include small mammals, lizards, and birds.

Behavior and reproduction: This snake is active at night. It hides during the day beneath rocks or in underground tunnels made by other animals. Unlike most snakes, the horned viper can dig into the ground and bury itself. It waits, often with just its horns above the ground, for a prey animal to walk nearby and then strikes and bites the animal. When it slithers, the horned viper slides sideways across the sand in what is known as sidewinding. This is an egg-laying snake, and the females lay between ten and twenty-three eggs at a time.

Horned vipers and people: Since it hides during the day, people rarely see the horned viper. It does, however, sometimes bite people, but the bites are not thought to be that dangerous.

Conservation status: This species is not considered endangered or threatened. ∎

COTTONMOUTH (Agkistrodon piscivorus): SPECIES ACCOUNTS

Physical characteristics: The cottonmouth gets its common name from the white, cottonlike color inside its mouth. Also known as the water moccasin, it is a large thick snake. Younger adults have brown or reddish bands on a yellowish background, while older individuals are usually all brown, greenish brown, or black. Juveniles have tails that are tipped with yellow or green. In the wild, adults may reach 5.9 feet (1.8 meters) in length and weigh 10 pounds (4.6 kilograms).

Geographic range: They are found in the southeastern quarter of the United States.

Habitat: The cottonmouth spends most of its time in or near the water, although it will sometimes crawl some distance onto land.

Diet: Cottonmouths will eat almost any animals they find. This includes birds, eggs, living and sometimes dead fishes, frogs, small alligators and turtles, snakes and other cottonmouths, and mammals.

Behavior and reproduction: Cottonmouths spend much of their time coiled up and out in the open. They hunt for food by swimming or slithering around looking for it or by staying still and waiting for the prey to mistakenly come a little too close. When they feel threatened, cottonmouths will strike and bite, but usually they remain motionless until the threat passes. Snakes that live in warmer areas are active all year, but those living in colder areas hibernate during the winter. During mating season, males sometimes fight one another for the chance to mate with a female. Females give birth to baby snakes instead of eggs in August or September. They have up to sixteen young at a time.

Cottonmouths and people: Although most cottonmouths are content to leave people alone, bites do occur. The venom is dangerous to humans and can be fatal. Humans also pose a great risk to the snakes by draining wetlands and otherwise destroying their habitat and also by killing the snakes out of fear.

Conservation status: This species is not considered endangered or threatened. ∎

TIMBER RATTLESNAKE (Crotalus horridus): SPECIES ACCOUNTS

Physical characteristics: The timber rattlesnake is a thick snake, often with dark, sometimes V-shaped blotches running down a black, dark or light brown, yellowish, or gray back. It has a large triangle-shaped head at one end and a black rattle-tipped tail at the other. Adults often reach nearly 5 feet (1.5 meters) in length, and some grow to more than 6 feet (1.8 meters).

Geographic range: They are found in much of the eastern United States.

Habitat: Timber rattlesnakes prefer rocky ledges on hills, although they travel into nearby forests, especially in the warmer months.

Diet: They have only six to twenty meals a year, but when they do eat, they hunt for mammals, and sometimes birds, lizards, frogs, insects, and other snakes.

Behavior and reproduction: Timber rattlesnakes spend much of their time either sunbathing, also known as basking, or sitting still to wait for their next meal to wander within striking distance. In the winter, this snake hibernates either alone or in groups. Females only mate once every two, three, or four years, giving birth to between three and nineteen live baby snakes at a time. The young snakes must reach four to nine years old before they can mate and have their own young.

Timber rattlesnakes and people: Bites to humans are uncommon but can be dangerous, although rarely fatal.

Conservation status: This species is not considered endangered or threatened. ∎

BLACK-HEADED BUSHMASTER (Lachesis melanocephala): SPECIES ACCOUNTS

Physical characteristics: As its name says, the top of the black-headed bushmaster's head is black. The back of this large snake has black diamond-shaped blotches on a dark or light brown or yellowish background. Adults often reach 6.6 feet (2 meters) in length but can grow to 7.9 feet (2.4 meters).

Geographic range: They are found in Costa Rica, possibly reaching into Panama.

Habitat: This species lives in wet or moist forests in valleys and other low places.

Diet: The black-headed bushmaster apparently eats mainly mammals.

Behavior and reproduction: A land-living snake, the black-headed bushmaster remains still much of the time, waiting for animals to wander by. If it is hungry, it will strike out and bite the passing animal. When it is not hunting, it often stays in underground tunnels made by other animals. If threatened, it may shake its tail. This is an egg-laying species, and females lay up to sixteen eggs. Unlike many reptiles, the female remains with her eggs until they hatch.

Black-headed bushmasters and people: If they are left untreated, humans bitten by this snake may die.

Conservation status: This species is not considered endangered or threatened. ∎

FOR MORE INFORMATION

Books

Brazaitis, Peter, and Myrna E. Watanabe. Snakes of the World. New York: Crescent Books, 1992.

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.

Campbell, Jonathan A., and William W. Lamar. 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." Contributions to Herpetology, Vol. 6. Oxford, OH: Society for the Study of Amphibians and Reptiles, 1990.

Harding, James. Amphibians and Reptiles of the Great Lakes Region. Ann Arbor, MI: University of Michigan Press, 1997.

Holman, J. Alan, and James Harding. Michigan Snakes. East Lansing, MI: Michigan State University Extension, 1989.

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

Lamar, W. The World's Most Spectacular Reptiles and Amphibians. Tampa, FL: World Publications, 1997.

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.