Iguanas, chameleons, geckos, and skinks are just a few of the many animals that make up the group of reptiles known as lizards. As one might expect in a group of more than 3,000 species, or types, there are many differences among members. For instance, while some lizards measure only an inch or two in length, the Komodo dragon can reach 10 feet (3 meters). But lizards also share some traits: most have dry, scale-covered bodies and long tails. All lizards are part of the scientific group Squamata.

Where lizards live

Lizards are cold-blooded animals, meaning that take on the temperature of their environment. Therefore they cannot live in extreme cold or heat. Most species prefer the warm parts of the world, where they are found in places ranging from wet tropics to dry deserts. In the United States, lizards are most numerous in the dry Southwest. Lizards can be found underground, on the ground, and in trees or plants. A few species spend some of their time in water.

Physical features

Lizards are vertebrates, or animals with a backbone. Most kinds have four strong legs, but some have very small limbs. Others have no legs at all. Among those with no legs are the glass lizards and the European slowworm. These lizards look much like snakes and are often mistaken for them. Unlike snakes, however, the lizards have eyelids and ear openings.

The scales that cover a lizard's body are small plates that are either smooth or bumpy. They are often brown, green, or grayish in color. At certain times, however, most lizards can change their color. Some drab lizards display bright color patterns when trying to attract a mate or scare away another animal. In addition, many lizards are able to change color to match their environment. The best-known lizards to do this are the chameleons. Within minutes a chameleon can take on the color of its surroundings—for example, by turning brown to look like part of a tree trunk. This form of protective coloration is called camouflage.

Lizards are notable for the variety of eye-catching features on their bodies. Some lizards have horns or spines. Others have a bony plate around the neck, called a frill. Such features help a lizard appear threatening to animals that would do it harm.

Behavior

Most lizards are active during the day. The geckos, however, are usually active from dusk to dawn. Different types of lizards have different ways of moving around. Most run on four legs, but some run fastest on their two rear legs. Legless lizards move like snakes do, by throwing the body into a series of S-shaped curves. A few lizards are able to glide through the air. These lizards have flaps of skin on the sides of the body between the front and hind legs. Spreading this skin allows them to glide from tree to tree.

Lizards spend much of their time looking for food. Some lizards eat seeds and plants, but insects are the most common part of the diet. Lizards may hunt for prey by digging, or they may lie in wait for prey to come near. A chameleon moves slowly while searching for prey and then shoots out its sticky tongue to capture it.

Lizards themselves are food for many birds, mammals, and reptiles. They protect themselves from these enemies in a variety of ways. Using camouflage and running away are two common methods for avoiding conflict. When an enemy must be faced, lizards often try to make themselves look bigger and tougher by puffing themselves up with air and standing high on their legs. Some lizards use their tails against an enemy as a whip. But lizard tails are used most effectively to escape enemies through trickery. The tails of many species break off when touched. The broken tail twists and wiggles, which draws the attention of the enemy while the lizard escapes. Most lizards are able to grow a new tail.

Two types of lizards, the Gila monster of the southwestern United States and the beaded lizard of Mexico, are poisonous. Their venom, or poison, is strong enough to kill a human. But they bite only when people bother them, and the victim very rarely dies.

Reproduction

Females of most lizard species lay eggs with tough, leathery shells. They hide the eggs in places where they will not be seen by enemies but can still be warmed by the sun. Most lizards lay several eggs at a time, but some species lay only one or two. In a few species, females tend their eggs until they hatch. Most lizards, however, leave the eggs after laying them. A few types of lizards give birth to live young instead of laying eggs.

Lizards and humans

Lizards are valuable to people in a number of ways. In some parts of the world large lizards, including iguanas, are eaten. Small types such as geckos, which tend to live around houses, are often welcomed because they eat insect pests. Lizards are also valued as subjects for scientific research because they are so varied and abundant.

Human activities, however, have threatened the survival of some lizard species. The most widespread danger to lizards is the destruction of their natural environment. This commonly happens when land is cleared to make space for buildings. The removal of lizards from the wild for sale as pets has also reduced the numbers of certain types. The great Komodo dragon of Indonesia, for example, was almost wiped out because of collectors. It is now protected by law.