COLUBRIDS: Colubridae

PHYSICAL CHARACTERISTICS

The colubrids (KAHL-yuh-bruhds) make up the largest group of snakes; they include almost 75 percent of all the world's snake species, or types of snakes. These snakes come in many sizes, shapes, and colors. Despite the many differences among the snakes in this family, colubrids share a few features. Most have wide scales on their bellies and, usually, nine large scales on the tops of their heads. Most colubrids also have glands, or groups of cells, behind each eye. These glands squeeze out a mixture of chemicals that, in some species, oozes through enlarged back teeth, known as rear fangs. When a colubrid bites down on a prey animal, this venom, or poison, trickles into the prey animal; the venom slows down, knocks out, or kills the animal, which the colubrid then eats. Unlike the cobras and vipers, whose fast-acting venom can knock out or kill an animal in moments, the colubrids produce venom that is not as strong and usually takes many minutes to work. The boomslangs and a few other species are exceptions to the rule; they have venom powerful enough to kill humans. Antivenin (an-tee-VEH-nuhn), a remedy that neutralizes, or makes ineffective, the poison of the snake, is available to treat the bites.

Colubrid snakes range widely in size, with some species growing to about 6 inches (15.2 centimeters) and others reaching 12 feet (3.7 meters) in length. Depending on the species, males may be larger than females, or females may be larger than males.

GEOGRAPHIC RANGE

Colubrid snakes occur almost everywhere in the world. The only places they do not live are Antarctica; the far northern reaches of Europe, Asia, and North America; and central and western Australia.

HABITAT

The snakes in this family make their homes in many different places. Some spend most of their time underground, some climb into trees and shrubs, some slither about mostly on the ground, and others live mainly in water. Most of the water-living colubrids like freshwater habitats, but a few, like the crab-eating water snake, can live in saltier water. A particularly unusual colubrid is the Southeast Asian flying snake, which not only climbs trees but also soars from one tree branch to another. These snakes do not actually fly but instead flatten out their bodies and soar from a higher branch to a lower one.

DIET

Depending on the species, colubrids may eat mammals, lizards, baby turtles, frogs and toads, fishes, earthworms, scorpions, tarantulas, some insects, and any number of other animals that will fit in their mouths. Some colubrids will eat almost anything that comes their way. Others will eat only a handful of different food items, and a few are extremely picky about their meals. For example, the rainbow snake dines on eels and little else, and the egg eaters of Africa swallow only whole bird eggs. In some species, snakes that eat one type of prey as youngsters continue eating that type of prey into adulthood. Many common garter snakes that grow up eating earthworms, for example, stick to a mostly earthworm diet as adults.

BEHAVIOR AND REPRODUCTION

Scientists have not studied the activities of most of the 1,700 colubrid species in any detail, because many of them live underground or in trees, or else they have excellent camouflage (KA-mah-flahzh), a sort of disguise, which makes them difficult to watch. Scientists do, however, have a lot of information about the more common snakes and even some particularly odd types. The most obvious features of many colubrids are their defensive methods. Often, snakes make their bodies appear bigger to scare off attacking animals, known as predators (PREH-duh-ters). For instance, the false water cobras spread their necks into a hood, giving them the look of much larger snakes. Some colubrid snakes will open their mouths wide and might even strike and bite. Many, including the northern ribbon snake, give off bad-smelling substances to convince predators that they should leave them alone.

A wide variety of colubrid snakes find that the best way to keep away from predators is to move away as quickly as possible. Other snakes act like venomous (VEH-nuh-mus), or poisonous, species, or they have coloring that copycats the coloring of venomous species. For example, the scarlet kingsnake has no dangerous venom, but it looks very much like the venomous eastern coral snake, and the milk snake, that has no dangerous venom, will wiggle its tail just as a venomous rattlesnake does.

Many colubrids that live in cool climates, particularly those with very cold winters, will hibernate (HIGH-bur-nayt), or become inactive and sleep deeply, to help them survive the frigid (FRIH-juhd) weather. Although most snakes do not dig, they will use other animals' underground homes as places to hibernate. Snakes will also sometimes hibernate among tree roots; inside old, rotting tree stumps; or in any other protected spot they can find.

During mating season, which usually happens once a year, the males of many colubrid species will wrestle with one another. In these fights two snakes usually twist their bodies around each other while trying to tip over the opponent. The winner approaches the female to mate. In some species, the male flicks his tongue at the female and presses his head against the female's back before mating. Tongue flicking is also used in hunting. Snakes do not really have a sense of smell. When a snake flicks out its tongue, it picks up scent (SENT) chemicals from the air. The snake then presses its tongue against the roof of its mouth and "smells" the scent, or odor, in that way.

A SNAKE MELTING POT

When considering all of the snakes in the world, nearly three of every four species is a member of the family Colubridae. Scientists have been struggling for many years to decide for sure if all of these snakes should remain in one large family or be split up into several smaller families. For now, however, they are all in one large family that is divided into smaller groups, called subfamilies. Not everyone agrees on the arrangement of the snakes in these subfamilies or even on the number of subfamilies, however, so plenty of work is left to do.

Most colubrid snakes lay eggs, but some females give birth to live snakes. Typically, the females lay eggs in a hole or tunnel in the ground or under some rotting leaves. The smaller species have fewer young than the larger species. Some of the smallest colubrids, such as the worm snakes, may lay only three eggs at a time, while larger species, like mud snakes, may lay more than thirty eggs. The diamond-backed water snake gives birth to nearly fifty live young at a time. For some species, the female's duties are complete as soon as she gives birth, but for others, the female will stay near her nest and protect her eggs.

COLUBRIDS AND PEOPLE

Humans are much more dangerous to colubrids than colubrids are to humans. People collect the snakes for pets or for food and, occasionally, for their skins, which are made into leather. For their part, most colubrids are of no danger to humans. Even those species with large or grooved rear teeth that can inject humans with mild venom typically do little more harm with their bites than to cause a bit of swelling at the bite spot. A few unusual species, including the boomslangs and twig snakes of Africa, have venom powerful enough to kill humans.

CONSERVATION STATUS

The World Conservation Union (IUCN) lists one species as Extinct, meaning that none is still alive. Six species are Critically Endangered, meaning that they face an extremely high risk of extinction in the wild, and seven are Endangered, meaning that they face a very high risk of extinction. Eight are considered Vulnerable, meaning that their risk of extinction is high, and four are Near Threatened, meaning that they may face the risk of becoming threatened with extinction in the near future. The U.S. Fish and Wildlife Service lists seven U.S. species and one foreign colubrid as Threatened.

The danger to most colubrid populations comes from the destruction of their habitat, or their preferred living areas, and their collection for the pet trade, food, or leather. While many species are finding it hard to survive, the brown tree snake is doing very well. This slender snake grows to 4.5 to 6.5 feet (1.4 to 2 meters) in length. It is native to Indonesia, New Guinea, Australia, and the Solomon Islands, but it seems to have hitched a ride on military ships during World War II to the Pacific island of Guam. Once there, it quickly adapted to its new home and has since hunted and eaten to extinction several species of the island's native birds and lizards.

BOOMSLANG (Dispholidus typus): SPECIES ACCOUNTS

Physical characteristics: A long, thin snake, the boomslang comes in a number of colors, including green, reddish, and black with yellow spots inside each of the black scales. The belly is often a creamy color. The boomslang has a large head and big eyes. Adults are about 4 feet (1.2 meters) long.

Geographic range: The boomslang lives in the central and southern regions of Africa, which is known as sub-Saharan Africa.

Habitat: This snake spends most of its time crawling among the branches of trees and shrubs in forests and grasslands.

Diet: It feeds on a variety of animals that it finds in trees and shrubs, including birds and chameleons (kuh-MEEL-yuns), a type of lizard.

Behavior and reproduction: Active during the day, the boomslang hunts for food above the ground in trees and shrubs. This snake, which has rear fangs, will bite and inject venom into prey and into attacking animals. The boomslang is an egg-laying species, and females lay about twelve eggs at a time.

Boomslangs and people: If the boomslang feels threatened, it may bite a person and inject its venom. The venom can be deadly to humans.

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

COMMON GARTER SNAKE (Thamnophis sirtalis): SPECIES ACCOUNTS

Physical characteristics: The common garter is a somewhat thin snake that may be brown, greenish, or red and may have blackish blotches. Garters usually have three long stripes running from top to bottom: a center stripe that may be almost cream in color and two yellow stripes along the sides of the body. Adults range from about 20 to 28 inches (51 to 71 centimeters) in length, but some can reach more than 4 feet (1.2 meters). Females and males look alike, but females are typically a bit larger than males and have shorter tails. Males' tails make up about 25 percent of the snake's overall length, while female tails make up about 20 percent.

Geographic range: This snake lives in Canada, the United States, and Mexico. Some populations live as far south as Florida and northern Mexico, while others live as far north as Canada and into the southern part of the Northwest Territories.

Habitat: Garters thrive in many habitats, including marshy spots, fields, and forests, especially near water. They also will enter freshwater areas for short periods of time.

Diet: Active during the day, garters eat a variety of animals, including insects, frogs, and small fishes, birds, and mammals.

Behavior and reproduction: Common garters that live in warm southern climates are active all year long. Those that live in the north hibernate during the coldest months. Hibernating males become active a bit earlier in the spring than the females, and mating occurs almost as soon as the females awaken. Females give birth to about ten to fifteen live young.

Common garter snakes and people: Most people know the garter as the snake seen in a garden. In fact, some people call it a "garden snake," and unfortunately many kill these harmless animals. These snakes may also die from encounters with cats and dogs, cars, and lawn mowers. Garters are common pets.

Conservation status: The IUCN does not consider this snake species to be threatened. The U.S. Fish and Wildlife Service lists one subspecies, called the San Francisco garter snake, as Endangered. The danger for this subspecies comes from loss of its habitat. A subspecies is a small group within a species that typically lives in a particular area and usually has a slightly different look from the rest of the animals in the species. ∎

MILKSNAKE (Lampropeltis triangulum): SPECIES ACCOUNT

Physical characteristics: Although all milksnakes have smooth, shiny scales, they can look quite different from one region to the next. Some have large red or brown blotches that are often lined in black on a gray to tan background; others have bands of red, black, and yellow or white. A few are solid black. Adults range from 20 to 60 inches (51 to 152 centimeters) in length.

Geographic range: The milksnake lives in North America, Central America, and South America. They make their homes throughout much of the New World, from southeastern Canada through all but the far western United States, into Mexico, Central America, and south to Ecuador and northern Venezuela.

Habitat: Milksnakes are common in forests and fields and sometimes live on rocky hillsides.

Diet: Young snakes seem to prefer eating other snakes, but adults round out their diet with small mammals, lizards, and bird and reptile eggs. A milksnake typically kills mammals and lizards by constriction (kun-STRIK-shun), which means that it coils its body around the prey animal and squeezes it to death.

Behavior and reproduction: The milksnake is a secretive animal during the day and usually stays under the bark of a tree, beneath boards, or in other small hiding places. It becomes active at night, when it feeds. Cold-climate milksnakes hibernate during the winter, often in groups. They mate in the spring. Females lay about ten eggs at a time, and the eggs hatch in one and a half to two months. When they reach three to four years of age, the young snakes are old enough to reproduce, or have their own young.

Milksnakes and people: Although the milksnake is not dangerous, people often kill it because it defends itself by shaking its tail, striking, and biting, the type of behavior that can make people think that it is a dangerous rattlesnake. Because the snake is sometimes found in barns, people at one time had the mistaken idea that it milked cows, and so they named it the milksnake. It is sometimes collected for the pet trade.

Conservation status: The milksnake is not endangered or threatened. ∎

EASTERN HOG-NOSED SNAKE (Heterodon platirhinos): SPECIES ACCOUNTS

Physical characteristics: The eastern hog-nosed snake has a thick body and a wide head with an upward-curving snout, or nose area. Its scales form ridges, or raised areas, and the snake's back usually is covered with brown spots scattered over a yellowish, orangey, gray, or olive green background. The spots, however, may be faded or missing entirely. Occasionally, a snake may be completely black. Adults are typically about 30 inches (76 centimeters) long, but they can grow to more than 45 inches (114 centimeters).

Geographic range: The eastern hog-nosed snake is found in Canada and the United States. It lives throughout most of the eastern half of the United States and into southern Ontario, Canada.

Habitat: This snake likes drier areas, including fields and forests.

Diet: Eastern hog-nosed snakes eat mainly toads, but they will also sometimes eat frogs, salamanders, and small mammals. Toads will often puff up their bodies with air to protect themselves from attackers, but hog-nosed snakes have long rear fangs that puncture and help deflate the toads in much the same way that a pin lets the air out of a balloon.

Behavior and reproduction: Some people call this snake a hissing adder, puff adder, or spread adder, because it spreads out its neck as a cobra does and makes loud hissing noises when threatened. If these defense moves fail, the snake may strike at the attacker, but almost always with its mouth closed. It does not actually bite. If necessary, the snake may follow up by vomiting, smearing its own waste over its body, or going into a squirming fit. As a last resort, it will roll onto its back, open its mouth with its tongue dragging, and play dead. If the attacker turns the snake onto its belly, it will promptly roll onto its back again as if it can play dead only when it is upside down. Once the attacker leaves, the snake turns over and scoots away.

This is an egg-laying snake. Females usually lay about twenty eggs at a time, although some lay up to sixty.

Eastern hog-nosed snakes and people: People frequently mistake this harmless snake for a venomous snake and kill it.

Conservation status: The eastern hog-nosed snake is not endangered or threatened. ∎

INDIGO SNAKE (Drymarchon corais): SPECIES ACCOUNTS

Physical characteristics: The indigo snakes that live in the southeastern United States are shiny black or bluish-black with a reddish throat. In tropical areas, their colors range from black to brown, gray, or yellow. Sometimes, the tail is a different color from the rest of the body. The longest snake in the United States, adults can reach nearly 10 feet (3 meters) long.

Geographic range: This snake lives from the southeastern United States south to northern Argentina in South America.

Habitat: Although it lives mainly on land, this snake often prefers areas near a water source, and it will dip into the water to chase prey. In the United States it tends to live in grasslands and shrubby spots with sandy soil, but it also may make its home in moist forests.

Diet: The indigo snake eats a variety of animals, including fishes and frogs, turtles, birds, mammals, and other snakes, including pit vipers.

Behavior and reproduction: Active during the day, this large snake spends much of its time searching for prey, which it bites at and swallows using its strength and size. Females lay about four to twelve eggs at a time. When the eggs hatch, the young snakes may be 2 feet (61 centimeters) long or more.

Indigo snakes and people: People often collect this usually gentle snake for the pet trade.

Conservation status: Although the IUCN does not consider the indigo snake to be threatened, the U.S. Fish and Wildlife Service lists it as Threatened in the United States. This large snake is popular in the pet trade. Its habitat is shrinking as people build in these areas. ∎

FOR MORE INFORMATION

Books:

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

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

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

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.

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

Lovett, Sarah. Extremely Weird Snakes. Santa Fe, NM: John Muir Publications, 1999.

Mattison, Chris. The Encyclopedia of Snakes. New York: Facts on File, 1995.

Mattison, Chris. Snake: The Essential Visual Guide to the World of Snakes. London: Dorling Kindersley, 1999.

Montgomery, Sy. The Snake Scientist. Boston: Houghton Mifflin, 2001.

Web sites:

"Eastern Garter Snake." Iowa Herpetology. http://www.herpnet.net/Iowa-Herpetology/reptiles/snakes/e.garter_snake.html (accessed on September 9, 2004).

"Eastern Hognose Snake." Iowa Herpetology. http://www.herpnet.net/Iowa-Herpetology/reptiles/snakes/e.hognose_snake.htm (accessed on September 9, 2004).

"Eastern Indigo Snake." University of Georgia Savannah River Ecology Laboratory. http://www.uga.edu/srel/eastern_indigo_snake.htm (accessed on September 1, 2004).

"Milk Snake." Iowa Herpetology. http://www.herpnet.net/Iowa-Herpetology/reptiles/snakes/eastern_milksnake.html (accessed on September 9, 2004).