Structure and Habits

Snakes are cold-blooded animals, and are found chiefly in the tropics and in temperate regions. There are none in New Zealand, Ireland, or where the subsoil is always frozen. Snakes hibernate during the winter in cold countries, and may also be inactive during very hot summers.

Many snakes, such as rattlers and garter snakes, may hibernate, or sleep, during the winter. Why do they do this? In many parts of the world, winter is too cold for snakes. They need warmer temperatures to help them keep their bodies working.

As winter approaches, snakes crawl into caves or holes in the ground to escape the cold. Often, many snakes will crowd into a single den to keep warm. Sometimes, more than one species of snake will share a den and sleep through the winter together.

While snakes hibernate, their body temperatures drop, and they stay fairly still. Hibernating snakes use up very little energy and do not have to worry about eating food. When spring arrives, they come out of their dens to warm up and to eat.

Snakes generally have compact heads that taper into their slender bodies. The head varies in shape among the different species. A pit viper, such as the rattlesnake of the United States, has a hollow, or pit, between eye and nostril. The pits are so sensitive to heat that they enable the snake to detect and strike a warm-blooded animal at some distance. The lower jaw of a snake is attached to the skull by elastic ligaments, permitting the snake to open its mouth wide enough to swallow whole animals much thicker than its own head. The elasticity of its skin also helps the snake to swallow large animals.

Snakes appear to have a fixed stare because their eyes have no lids; instead, the eyes are covered by a transparent protective membrane. The sense of smell is sharp. Snakes have no external ear or any eardrum, but the inner ear is well developed. They can hear only low-frequency sounds in the air, but can feel the vibrations that sound waves create in the ground.

All snakes have forked tongues. The tongue plays a role in the snake's sense of smell; in effect, it transmits odor to an organ of smell inside the mouth. For this reason, the tongue constantly flicks in and out, seeking the scent of prey. A snake's teeth are used for grasping prey rather than for chewing. They are sharp, cone-shaped structures that curve backward toward the throat. Venomous snakes, in addition, have two needle-sharp fangs, grooved or tubular so they can conduct a fluid from poison-secreting glands located in the head.

Snakes feed on a variety of living things, including insects, frogs, mice, snails, and birds. Some snakes eat other snakes. Some eat primarily bird eggs.

It is easy to see what is on the menu for some snakes—eggs. For others, dinner depends on the species of snake and where it lives. Snakes eat almost any animal that fits into their bodies—fish, frogs, lizards, birds, small mammals—even other snakes.

Like many snakes, egg eaters can eat food that is bigger than their heads. A few egg-eating snakes, such as the African egg eater, have special features for eating eggs. Pointed spines on the neck bones break through the eggshell, allowing the snake to swallow the liquid inside. Then muscles in the snake’s neck crush the shell, which is spit out. Other egg eaters, however, eat the whole egg—shell and all.

Snakes do not need to eat very often. One reason is that they don’t need the food energy to make their own body heat. The other reason is that snakes often eat big meals for their size, so they are not hungry again right away.

Most snakes strike and seize their prey from a coiled position, thrusting the front part of the body forward. Some, however, strike from other positions. Coral snakes, for example, strike by sideswiping the prey with the front of their bodies; a cobra elevates the front of its body and strikes with a forward or downward motion. Some species such as the boas and pythons, although capable of biting, immobilize their prey by coiling and constricting their bodies around the prey, thereby suffocating it.

A snake has a backbone, but no breastbone. Large snakes may have more than 400 vertebrae. Although snakes are limbless, some species show traces of hind limbs in the form of small spurs. Horny scales cover the body; their size, shape, number of rows, and color differ for each species.

Snakes glide or crawl forward with a slithering motion that is aided by muscular contractions of the body and the pushing of the scales against the ground. Snakes known as sidewinders move sideways rather than forward. Contrary to popular belief, snakes do not move swiftly. For example, the coachwhip, considered a fast snake, travels at about 3 mph (4.8 km/h).

In cooler climates, snakes usually mate in the spring, but in the tropics mating occurs at any time. The majority of snakes lay leathery, whitish eggs; the others give birth to live young. In some species, the female incubates the eggs by winding her body around them until they hatch. The number of young varies from 1 to more than 100, depending on the species and individual.

Most species of snakes lay eggs. Depending on the species, a female snake may lay as few as 6 eggs or as many as 100 eggs at one time.

Snake eggs have leathery shells. The shells stretch as the baby snake inside grows. After several weeks, the baby snakes are ready to hatch. A hatching baby snake has a special tooth—an egg tooth—that tears open the shell so that it can wriggle out. Soon after hatching, the baby snake sheds this tooth.

Female snakes lay eggs in holes, burrows, rotten logs, tree stumps, and other such places. A few species of snakes, such as pythons, coil around their eggs to protect them and keep them warm. But most snakes leave their eggs after laying them. The eggs are left to hatch on their own. Some don’t make it. The eggs are eaten by other animals.

The newborn snakes usually shed their skin soon after birth. Thereafter, skins are shed, or sloughed, completely from lip to tail as the snake grows and a larger skin is needed to accommodate the larger body.

More than 50 species of snakes are endangered. Part of the reason is that some people eat snakes. Other people wear snakeskin boots, shoes, and belts. Many snakes are overhunted for these reasons.

Some snakes are in danger because of changes to their habitats. This is true for San Francisco garter snakes. As more land is cleared for farms, homes, businesses, and roads, the snakes have fewer places to live.

Many snake deaths happen by mistake. Common water snakes are often killed by people who mistake them for cottonmouths. Some milk snakes are killed because they look a lot like coral snakes. It is true that poisonous snakes are dangerous. But most snakes are not poisonous.