Wormlizards: Amphisbaenidae

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WORMLIZARDS: Amphisbaenidae

WHITE-BELLIED WORMLIZARD (Amphisbaena alba): SPECIES ACCOUNT

PHYSICAL CHARACTERISTICS

The members of this family, known simply as wormlizards, are long, thin, legless animals. Their scales are arranged in rings around the body with each ring separated from the next by a shallow groove. This ring and groove pattern makes them look much like earthworms, even though the worms lack scales. In some species of wormlizard, the head is round. In others, it may be shaped like a shovel, or in some cases the snout may come to a point. They have no openings for their ears, as the lizards do, and they have only the smallest of eyes showing below a see-through scale, if they are visible at all. They have no legs, but all species in this family have tiny bits of hip bones inside their bodies. They do not, however, have a sternum (STER-num), which is the bone at the front of the chest that in most animal species connects to the ribs.

Most wormlizards reach about 10 to 16 inches (25 to 40 centimeters) long as adults, but some species are much smaller or much larger. The smallest species lives in Africa and only grows to 4 inches (10 centimeters) long, while the largest, known as the white-bellied wormlizard, can reach more than 32 inches (80 centimeters). A wormlizard's tail, which can look much like the rest of the body, actually starts at the vent, a slit-like opening on the underside of the animal. The tails in these animals are very short, usually less than one-tenth of the overall body length. The tails may be rounded, pointed at the end, or have a flattened shape. Many of the 160 species of wormlizards have about the same color: pale pink or pale orange-pink, sometimes with a whitish belly. Some species, however, are colored brown, yellow, purple, or gray, and a few even have eye-catching black-and-white patterns. The males and females of each species look alike.

The wormlizards in this family have many of the same features of three other families of animals: the mole-limbed wormlizards, the Florida wormlizards, and the spade-headed wormlizards. These four families all fall under the group called amphisbaenians (am-fizz-BAY-nee-ens). Like the wormlizards in this family, many of them look much like earthworms, and all except the mole-limbed wormlizards are legless. Interestingly, all wormlizards have only one lung, or one large lung and one tiny lung, and one larger tooth in the middle of the upper jaw. In those that have eyes, they have no eyelids. They also have a forked tongue and a thick, strong skull. They have an unusual hearing system that allows them to pick up even slight vibrations underground. In this system, a little structure attaches the ear to tissue on the side of the face. When they are slithering about, they can feel vibrations through the ground with the bottom of the face. The vibration then runs up the tissue and to the ear, which hears it. This ability, which lets the wormlizards hear even small movements made by other animals, comes in particularly handy when the wormlizards are looking for ants and other insects to eat.

GEOGRAPHIC RANGE

Wormlizards live in both the western and eastern hemispheres, including South America, Central America, the West Indies, Africa, Asia, and Europe. They tend to live in tropical areas or in spots with a slightly less warm, subtropical climate.

IS IT A WORM OR A LIZARD?

Is a wormlizard more like a worm that looks like a lizard, or a lizard that looks like a worm? Animals are split into two major groups: vertebrates, which have backbones, and invertebrates, which do not have backbones. Wormlizards and lizards have backbones, but earthworms do not, so wormlizards are more like lizards than earthworms. In fact, both wormlizards and lizards are reptiles, but wormlizards are not true lizards. Instead, wormlizards are a unique group of reptiles that mostly live underground, have rings of scales separated by shallow grooves, and have a number of other characteristics that separate them from the lizards.

HABITAT

Wormlizards stay out of sight most of the time, either remaining in their burrows or beneath rocks or leaf litter on the ground. Some of them make themselves at home in the nests of ants or termites, possibly even laying their eggs or having their young there. They will come out on the surface after particularly heavy rains that flood their underground homes.

DIET

Wild wormlizards eat mainly ants, termites, beetles, grubs (young beetles), caterpillars, and cockroaches. In one study, scientists looked inside the stomachs of wormlizards and found that some were filled with fungi. In another study, they found one wormlizard that had eaten a lizard, or at least its leg, and another that had swallowed a burrowing snake—whole. In captivity, wormlizards will eat other large vertebrates (VER-tehbrehts), which are animals with backbones, so some people believe they may do the same in the wild.

BEHAVIOR AND REPRODUCTION

Wormlizards are fossorial (foss-OR-ee-ul), which means that stay underground most of the time. Depending on the shape of the head, they dig their tunnels in different ways. Those with a round head butt their heads straight into the dirt like a battering ram and move forward that way. Other species with heads shaped like shovels, scoop up dirt onto the top of the head and then press it into the roof of the tunnel. Those with sideways-flattened heads, on the other hand, press the head and the body side to side and force an opening through the soil. No matter how they make their tunnels, they all use them to hunt for animals to eat. They mostly hunt by using their excellent hearing and by smelling. Like other amphisbaenians, wormlizards have forked tongues that pick up chemicals left by prey animals. They then touch their tongues to a small opening on the roof of the mouth that opens to a special organ. This organ, called a Jacobson's organ, can smell the chemicals.

Although wormlizards stay underground, which protects them from most predators, they sometimes come under attack. When this happens, most species can drop the tail, which can confuse a predator (PREH-duh-ter) enough to give the wormlizard time to escape. Unlike many of the lizards that also drop their tails, wormlizards cannot regrow theirs.

Scientists know little more about their behavior, courtship, or mating. The females of most species lay eggs, but some give birth to baby wormlizards. The number of eggs in each clutch is typically between one and four, although a few species can lay more than a dozen. Females sometimes lay their eggs inside ant or termite nests.

WORMLIZARDS AND PEOPLE

Wormlizards and people rarely run across one another.

CONSERVATION STATUS

None of these species is considered endangered or threatened.

WHITE-BELLIED WORMLIZARD (Amphisbaena alba): SPECIES ACCOUNT

Physical characteristics: Among the largest members of the family, the white-bellied wormlizard can grow to 33.4 inches (85 centimeters) long with a body that can reach up to 2 inches (25 centimeters) wide. Adults can, however, be much smaller, growing to only half that size. Of their total length, only 6 percent is tail. Like other wormlizards, their scales form rings around the body and give the animal an earthworm-like appearance. The scales on their back are small and square. They have a rounded head with one large tooth and six smaller ones in the front of the upper jaw.

Geographic range: The white-bellied wormlizard lives in Panama, which is in far southern Central America, in the West Indies, and in South America east of the Andes Mountains.

Habitat: This burrowing animal almost always stays in its underground tunnels, buried under dead leaves, or inside the nests of leaf-cutter ants.

Diet: With its strong jaws, the white-bellied wormlizard can eat animals as large as mice and rats in a scientist's laboratory. In the wild, however, they are known only to eat smaller animals, such as ants, termites, crickets, and other insects, as well as spiders and other invertebrates (in-VER-teh-brehts), which are animals without backbones.

Behavior and reproduction: Unlike other wormlizards that drop the tail when they feel threatened, this species cannot. Instead, it curls up its body so the head and tail are next to one another, and then raises its head and opens wide its mouth while lifting up and swaying its tail. This behavior makes the wormlizard almost look as if it has two heads, and, in fact, some people call it a "two-headed snake." Females lay eight to 16 eggs at a time, probably once a year during the dry season.

White-bellied wormlizards and people: White-bellied wormlizards and people rarely run across one another.

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