Snake

Snake, legless reptile related to the lizards. There are about 2,700 species, most of which live in tropical countries, though a few survive in nearly arctic conditions. Snakes do not have legs, although the boas and pythons have the remains of a hind pair of legs. It is thought that they evolved from burrowing, legless lizards. Snakes, unlike lizards, do not have eardrums and are deaf to airborne sounds (they cannot hear the snake charmer's flute), but they can sense sounds coming through the ground by their vibrations. Locomotion is achieved by several methods. In the common serpentine movement, the body is pushed forward in S-shaped waves. In concertina movement the body is thrown forward in loops. Large snakes can push themselves along by movements of the belly scales. The sidewinder and the horned viper move over loose sand by throwing the body into S-shaped waves in side-winding locomotion.

Snakes feed on live animals or eggs. They kill their prey by constriction—preventing it from breathing but not crushing it—or by biting. Poisonous snakes inject venom through grooved or hollow fangs from modified saliva glands. Hematoxic venoms attack the blood and nervous system; and neurotoxic venoms attack the nerves. The young hatch from eggs or are born alive. The mother may look after the eggs; otherwise they are left in a nest in soil or under a log. Snakes grow throughout their lives and shed their skins every year or so.