SPADE-HEADED WORMLIZARDS: Trogonophidae

PHYSICAL CHARACTERISTICS

At first glance, the spade-headed wormlizards look like big earthworms. Just as earthworms have rings around their bodies, these wormlizards have thin rings from the back of the head to the tip of the tail. Such rings are called annuli (ANN-youlie). In the spade-headed wormlizards, the rings are made of tiny square-shaped scales that are the same size and shape from the belly to the back. Also like earthworms, the wormlizards have no legs. Wormlizards, however, do still have tiny leftover hip and shoulder bones inside their bodies.

The heads of spade-headed wormlizards are shaped like shovels, or spades, which gives them their name. Sometimes, people also call them by another common name, short-headed wormlizards, because their heads are quite small and end quickly after the neck. The edges of the face are quite sharp, providing an excellent digging tool for these burrowing animals. The body is flattened into an upside down "U" shape, so that the wormlizard has a rounded back and an inward-curved belly side. It has a very short, sometimes ridged, or keeled, tail. The tail begins at the vent, a slit-like opening on the underside of the animal.

Some spade-headed wormlizards are patterned with checks and spots. They are rather small animals, with adults ranging from 3.1 to 9.4 inches (8 to 24 centimeters) in length.

GEOGRAPHIC RANGE

They live in northern Africa, in eastern Somalia, and in the Middle East from western Iran to the island of Socotra, which lies east of Somalia and south of Saudi Arabia.

HABITAT

Spade-headed wormlizards tunnel in loose soils, which may be sandy or loamy. A loamy soil is one that is not quite as grainy as sand but still is quite loose.

DIET

Most of the spade-headed wormlizards eat termites, grubs, and ants. Grubs are actually young beetles, which are also known as beetle larvae (LAR-vee). When the grubs are old enough, they go through another life stage called pupae (PYU-pee) and then turn into the adult crawling beetles familiar to most people. Wormlizards in captivity will also eat larger animals by biting off chunks and chewing them up. Scientists are unsure if they eat larger animals in the wild because they have never seen a wild wormlizard eating a larger animal. On the rare occasions when they have been able to catch and cut open a wild wormlizard to check its stomach and see what it had been eating, scientists have not found pieces of large animals inside. Until more studies on wormlizards are done, scientists cannot say for sure whether they eat larger animals in the wild.

LIZARD EARS

On a person, a dog, or a cat, the ears are obvious. They are called "external" ears because external means something that is on the outside. Some animals, including many reptiles, have no external ears. Instead, their ears are often little more than holes on the sides of the head. Some species do not even have the holes. They are covered with scales. Spade-headed wormlizards are an example of reptiles without external ear openings. They can, however, still hear and are especially good at hearing vibrations in the soil. Such vibrations could be made by a predator walking overhead or a prey animal moving about.

BEHAVIOR AND REPRODUCTION

These wormlizards move oddly when they are tunneling. Instead of forcing their heads forward into the soil, they turn their heads up on one side and then up on the other, scraping the sharp sides of the face in this back-and-forth swiveling motion, and scrape away dirt. Just as twisting an apple corer will cause the corer to cut into and through an apple, swiveling the head of one of these wormlizards slices into the soil to make a tunnel. This swiveling motion is known as oscillation (AH-sih-LAY-shun). Besides cutting through the soil, the oscillation packs the dirt against the sides of the tunnel to make it smooth and rather strong. Although the head turns back and forth, the rest of the wormlizard's body does not. Its body's upside down "U" shape helps the wormlizard grab hold of the soil with its belly side and keep its body still. In addition, its very short tail digs in to the bottom of the tunnel to hold the body in place while the head swivels.

Because they have tiny eyes, if they have them at all, these wormlizards do not rely on vision to find their prey. Instead, they have excellent senses of hearing and smell. Although their ears are hidden by scales, they can hear even small movements, like a termite taking a few steps somewhere else in the soil. They also stick out their forked tongues to pick up chemical odors, then draw the tongue back inside the mouth to touch a special organ on the roof of the mouth. This organ, called the Jacobson's organ, smells the chemical odor.

Their underground homes provide considerable protection against predators (PREH-duh-ters), or animals that hunt other animals for food. Sometimes, when they are on the surface, however, they may face a predator. Unlike wormlizards in other families, the spade-headed wormlizard cannot drop the tail, a tactic that other species use to escape attackers. Instead, wormlizards roll over to be belly-up, and they stop moving. Predators may be surprised by the color or the belly or may lose interest because the wormlizard is so still. Either way, this behavior apparently helps the wormlizard to live another day.

The females of some species of these wormlizards give birth to about five baby wormlizards at a time. Scientists believe that some other species lay eggs. Little else is known about the courtship, mating, or reproduction of these animals.

SPADE-HEADED WORM LIZARDS AND PEOPLE

Although people rarely see these wormlizards, they may be helpful to people because they eat pest insects such as ants and termites that might damage the wood in buildings or cause other problems for people.

CONSERVATION STATUS

These species are not considered endangered or threatened, but scientists know little about them in the wild.

NO COMMON NAME (Agamodon anguliceps): SPECIES ACCOUNT

Physical characteristics: Agamodon anguliceps has a short shovel-shaped head and a sharp-sided face. Its back is mottled with yellow and dark brown to brownish purple blotches, and its underside is pink to purplish pink. Its tiny squarish scales form rings around its body. It grows to about 4 to 8 inches (10 to 18 centimeters) in length.

Geographic range: This species lives in eastern Ethiopia and Somalia along the eastern edge of central Africa.

Habitat: They tunnel in loose and sandy soils.

Diet: Scientists have not studied this animal in the wild, but they suspect that it eats termites, grubs, and other invertebrates (in-VER-teh-brehts), which are animals without backbones. In captivity, however, this wormlizard can also attack and kill larger vertebrate prey, which they then eat by biting off and chewing up the pieces. Vertebrates (VER-teh-brehts) are mammals and other animals that have backbones.

Behavior and reproduction: Like other members of this family, this species digs its tunnels by swiveling its head and using the sharp sides of its face to slice through the soil. It appears to stay closer to the surface of the ground during the night and move deeper into the soil in the daytime. When it feels threatened, it flips onto its back to show off its pink underside and then plays dead. Scientists know almost nothing about its reproduction, but they believe that the females probably lay eggs.

Agamodon anguliceps and people: People and this wormlizard rarely see one another.

Conservation status: This species is not considered endangered or threatened, but scientists know little about them in the wild.

FOR MORE INFORMATION

Books:

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

Gans, C. Biomechanics: An Approach to Vertebrate Biology. Philadelphia: J. B. Lippincott Company, 1974.

Schwenk, K. Feeding: Form, Function, and Evolution in Tetrapod Vertebrates. San Diego: Academic Press, 2000.

Vanzolini, P. E. Evolution, Adaptation and Distribution of the Amphisbaenid Lizards (Sauria: Amphisbaenidae). Ph.D. diss. Harvard University, 1951.

Web sites:

"Amphisbaenia." Virtual Museum of Natural History. http://www.curator.org/LegacyVMNH/WebOfLife/Kingdom/P_Chordata/ClassReptilia/O_Squamata/InfraAmphisbaenia/amphisbaenia.htm (accessed on November 15, 2004).

"Family Trogonophidae (Shorthead Worm Lizards)." EMBL Reptile Database. http://www.embl-heidelberg.de/uetz/families/Trogonophidae.html (accessed on November 15, 2004).

"The Keeping and Maintenance of Amphisbaenians." Cyberlizard. http://www.nafcon.dircon.co.uk/amphisb1.html (accessed on November 15, 2004).

"Order Squamata, Suborder Amphisbaenia (worm-lizards)." San Francisco State University. http://online.sfsu.edu/uy/AnimDiv/lab/lab8/Biol171Lab8.html. (accessed November on 15, 2004).