SLENDER BLIND SNAKES, THREAD SNAKES, OR WORM SNAKES: Leptotyphlopidae

PHYSICAL CHARACTERISTICS

Slender blind snakes, which are also known as thread snakes or worm snakes, are thin snakes with smooth, shiny scales. Members of this family look much like blind snakes of the family Typhlopidae and the early blind snakes of the family Anomalepididae, since all have tube-shaped bodies that are about the same diameter from head to tail, and all have short heads with mouths that open downward instead of right on the front end of the head. Species within the three blind snake families have small eyes and bodies that are covered with small scales that are the same size on the belly as they are on the sides and back. In most snakes, the belly scales, or ventrals, are noticeably larger. In the three blind snake families, only the scales on the snout are larger.

The slender blind snakes are different from the other two families in several ways. While all are slim, the slender blind snakes are the thinnest. The bodies of most species within this family are no wider than 0.2 inches (0.5 centimeters), and some are as little as 1/25th of an inch (1 millimeter) wide. This gives them the appearance of moving string or thread. The largest species in the family, such as the western slender blind snake (also known as the southwestern thread snake) and the western thread snake, may reach more than 15 inches (38 centimeters) in length, but most of the 93 species in the family are much smaller. The typical adult ranges from 4 to 10 inches (10 to 25 centimeters) in length and no more than 0.05 ounces (1.4 grams) in weight. Another characteristic that sets the slender blind snakes apart from the other blind snakes—and indeed from all other snakes—is their teeth. Slender blind snakes are the only snakes that have teeth on the lower jaw, but none on the upper jaw.

Most slender blind snakes have backs that are all one color. They may be pink, light or dark brown, black, or gray. A few South American species are colorfully striped. The tails vary in length from about 2 percent of the overall body length to 19 percent, but most have tails that take up about 5 to 10 percent of the total length. The tail on a snake begins at the vent, which is a slitlike opening on the underside and toward the rear of the animal. The tail in almost all species of slender blind snakes has a sharp spine on the end. Most have rounded snouts, but some have hooked and/or pointed snouts. In one unusual species, known as the western slender blind snake, the largest of its snout scales glows under ultraviolet light. Inside the body, the skeleton of most slender blind snakes includes pieces of hip and upper leg bones that are leftover reminders of its ancient ancestors, which had working hips and legs. In boas and other snakes that have similar structures, the bony bits sometimes stick out of the body near the vent and look like small claws. These "claws" are called spurs. In slender blind snakes, the leftover bones usually do not poke through the skin. A few species have another odd feature in their skeletons: The top of the skull is missing.

GEOGRAPHIC RANGE

Slender blind snakes live in South, Central, and North America, as well as Africa and southwest Asia. North American species live in Mexico and the southwestern United States. Certain species also live on the island of Socotra in the northwestern Indian Ocean, in the West Indies, and on islands off the coast of Africa, Mexico, and Central America.

HABITAT

Slender blind snakes can live in many different habitats from dry deserts and humid rainforests to rocky mountainsides, but within those habitats, they always seek at least slightly damp areas. These burrowing snakes spend much of their day buried under an inch or two (2.5 to 5 centimeters) of soil, hidden beneath stones or logs, or out of view in piles of rotting leaves or inside ant and termite hills. The species known only by its scientific name of Leptotyphlops natatrix may be a swimmer. Just one individual from this species has ever been found, and it was discovered in 1931 in a swamp in Gambia.

DIET

Slender blind snakes eat small invertebrates (in-VER-teh-brehts), which are insects and other animals without backbones. Many of the species will eat almost anything, including insects such as caterpillars, fly maggots, beetles, cockroaches, and crickets, as well as spiders, harvestmen, which include daddy longlegs, and the many-legged centipedes and millipedes. Most species, however, tend to prefer ants and termites. The snakes are able to find ant and termite hills by following the chemical trails that these insects leave on the ground as they travel to and from the nest. Once the snake tracks down the ant or termite hill, it slithers inside and eats as much as it can. In ant hills, they especially like the eggs, larvae (LAR-vee), and pupae (PYU-pee). Ant eggs hatch into larvae, which are the maggotlike life stage of ants. Eventually, the larvae transform into the motionless pupae stage before becoming adult ants. The slender blind snakes are able to jut out and pull in the lower jaw very quickly, which allows them to eat hundreds of eggs, larvae, and pupae in a very short time.

Many animals avoid ant hills because these insects, which are very protective of their nests, can bite and sting. The slender blind snake, however, is able to defend itself. When attacked, the snake rolls into a ball and smears itself with its body's own ant repellant: a mixture of slime and feces. The ants shy away from the smelly mess, leaving the snake to return to its meal.

SIZE MATTERS

Some animals need to live in a moist environment. The slender blind snakes, for example, burrow underground, hide beneath rocks, or slither into rotting logs or piles of dead leaves. One of the reasons a slender blind snake needs moisture is its very high surface-to-volume ratio. This is a mathematical formula that shows how much outer surface, or surface area, an animal has compared to the space, or volume, the entire animal takes up. Because the slender blind snake is so long and thin, it has a great deal of surface area compared to its overall tiny body. If the snake were round like a ball rather than long and thin, its surface area would be much, much smaller. The outside weather has a greater effect on animals with higher surface-to-volume ratios, because a higher percentage of their total body volume is exposed. This means that they can dry out especially fast and may even die. For this reason, these animals frequently live in moist habitats or underground where their surroundings are damp.

BEHAVIOR AND REPRODUCTION

Slender blind snakes spend most of their time out of sight and below ground, sometimes as much as 49 feet (15 meters) down, but they will crawl out of their burrows at night or after a heavy rain. They are able to dig through loose, sandy soil but cannot dig into harder ground, so they probably use other animals' burrows or perhaps crawl along the paths of plant and tree roots when they are in tougher soil conditions. If they feel threatened, the snakes will squirm wildly, and those with tail spines will jab their attacker. Some species may also stiffen up their bodies and play dead in an attempt to survive an attack.

Although they are not sure, scientists suspect that all species lay eggs, rather than give birth to live baby snakes. The few snakes that have been studied mate in the spring and lay one to twelve eggs at a time in the summer.

SLENDER BLIND SNAKES AND PEOPLE

These snakes and humans rarely encounter one another.

CONSERVATION STATUS

These snakes are not listed as endangered or threatened.

TEXAS BLIND SNAKE (Leptotyphlops dulcis): SPECIES ACCOUNT

Physical characteristics: With their brownish pink to dark brown coloration, Texas blind snakes look much like earthworms, except that the snakes have noticeable scales and lack the worm's segments. The snakes have a lighter colored, sometimes almost white, underside. Also known as Texas thread snakes, they have a long, thin body and a small head with eyes that appear as little more than tiny dark spots. Adults range from 2.6 to 10.7 inches (6.6 to 27 centimeters) long. The tail is short, just 5 to 6 percent of total body length, and has a spine at the end.

Geographic range: Texas blind snakes are found in the southwestern United States and northeastern Mexico.

Habitat: Also known as a Texas worm snake, the Texas blind snake spends much of its time in the dirt, under rocks, or in some other hiding place. It can live in dry areas, including deserts and rocky mountainsides, but often chooses a spot near a water source.

Diet: Texas blind snakes most often eat ant larvae and pupae and termites, but they sometimes eat other insects and spiders. They always eat ant larvae and pupae whole, but they often refuse to eat the heads of termites and sometimes only chew the juices out of the back portion of the termite. Once in a while, a small owl known as a screech owl will swoop down to snatch a Texas blind snake and, keeping it alive, bring it back to its nest. There, the snake cleans out the nest by eating small invertebrates that might otherwise nibble on the owl.

Behavior and reproduction: Texas blind snakes live mainly underground but sometimes crawl out of their burrows at night or after a rain downpour. They are not especially good at slithering above ground and sometimes jab the tail spine into the ground to push off. Males and females group together in the spring for the mating season. The female lays two to seven eggs in June or July and then coils around them. Often, several females lay their eggs near one another. The eggs hatch in late summer into baby snakes about 2.6 to 3 inches (6.6 to 7.6 centimeters) long.

Texas blind snakes and people: Texas blind snakes and people rarely encounter one another.

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

FOR MORE INFORMATION

Books

Brazaitis, P., and M. Watanabe. Snakes of the World. New York: Crescent Books, 1992.

Burnie, David, and Don Wilson, eds. The Definitive Visual Guide to the World's Wildlife. New York: DK Publishing, 2001.

Grace, Eric, ed. Snakes. San Francisco: Sierra Club Books for Children, 1994.

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

McDiarmid, R. W., J. A. Campbell, and T. A. Touré. Snake Species of the World. A Taxonomic and Geographic Reference. Vol. 1. Washington, DC: Herpetologists' League, 1999.

Mehrtens, John M. Living Snakes of the World in Color. New York: Sterling Publishing, 1987.

Shaw, C. E., and S. Campbell. Snakes of the American West. New York: Alfred A. Knopf, 1974.

Taylor, Barbara. Snakes. New York: Lorenz, 1998.

Werler, J. E., and J. R. Dixon. Texas Snakes: Identification, Distribution, and Natural History. Austin: University of Texas Press, 2000.

Web sites

"Family Leptotyphlopidae (slender blind snakes and thread snakes)." Animal Diversity Web. http://animaldiversity.ummz.umich.edu/site/accounts/information/Leptotyphlopidae.html (accessed on September 29, 2004).

"Other Interesting Aspects of Ant Biology." Rice University. http://www.ruf.rice.edu/bws/blindsnake.html (accessed on October 7, 2004).

"Photographs of Blindsnakes." Comparative Physiology and Biomechanics Lab at the University of Massachusetts Amherst. http://marlin.bio.umass.edu/biology/brainerd/kleyphotos.html (accessed on October 7, 2004).

"Texas Blind Snake." National Wildlife Federation. http://www.enature.com/fieldguide/showSpeciesSH.asp?curGroupID=7&shapeID=1060&curPageNum=1&recnum=AR0724 (accessed on October 7, 2004).