Snake (reptile)

Article Outline

Introduction; Physical Characteristics; Locomotion; Behavior; Reproduction and Life Cycle; Conservation Status

Introduction

Snake (reptile), legless animal with a long, flexible body covered with overlapping scales. Snakes are reptiles, a diverse group of animals that also includes lizards, turtles, and crocodiles. Snakes are thought to have evolved from lizards and share many characteristics with this group—particularly the so-called legless lizards, which have tiny, almost imperceptible legs. But unlike most lizards, snakes have thin, forked tongues, and they lack external ears. And while most lizards have movable eyelids that periodically close to protect and lubricate the eyes, a snake’s eyes are always open, protected by immobile, transparent scales.

Like all reptiles, snakes are cold-blooded, or more correctly, ectothermic—that is, they cannot produce their own body heat. Instead, they rely on the sun to heat their bodies and then regulate their temperature with behavior. Because they do not rely on energy from food to generate body heat, snakes can survive on an extremely meager diet. Some wait for months between successive meals, and a few survive by eating a single, large meal just once or twice a year. When they do eat, snakes swallow their prey whole rather than biting off small pieces. Many snakes have specialized jaws that enable them to swallow animals that are far larger than their own heads. Although uncommon, some snakes, such as the African rock python, have been observed eating animals as large as an antelope or a small cow.

With over 2,500 species belonging to more than 10 families, snakes are a large and successful group. They owe much of this success to their versatility—snakes occupy habitats ranging from underground burrows to the tops of trees to ocean depths as great as 150 m (490 ft). They are found on every continent except Antarctica, and although they are most abundant in tropical areas, many survive in regions marked by extreme cold. The range of the European adder, for instance, extends north of the Arctic Circle. The only places without snakes are parts of the polar regions and isolated islands, such as Ireland and New Zealand.

Physical Characteristics

Print this section

Although all snakes have a long, cylindrical body, many species boast unique modifications suited to particular habitats and lifestyles. Burrowing snakes, for example, have muscular, stout bodies and solidly built heads that they use to push through soil. Sea snakes have flattened, paddlelike tails for swimming, and the long, thin shape of many arboreal, or tree-dwelling, snakes provides agility when navigating between branches. Some snakes, including pythons, retain characteristics that reflect their evolution from lizards or from lizardlike ancestors. These snakes have traces of hind limbs called spurs, which are usually more prominent in males than in females.

Skin

Snake bodies are covered in overlapping scales composed of a horny material called keratin. These transparent scales make up the dry, smooth, outer layer of skin, whose primary function is to prevent water loss. Snakes owe their coloration to pigment cells located in the skin layer below the scales. Most snakes display drab earth tone colors to blend with their natural surroundings. Arboreal species, such as the emerald tree boa, are often vibrant shades of green, a coloration that helps them hide among leafy foliage. Some snakes, such as coral snakes, have brilliant yellow and orange stripes that warn predators of their venomous bite.

Snakes regularly shed the outer layer of their skin as they grow. Even in snakes that are not growing, the scales become drab and worn over time, and must be periodically replaced by a new, healthy layer. Some species of snakes shed their skin about every 20 days, but other species shed it only once a year. In the shedding process, a new layer develops below the surface of the old one, which gradually separates in preparation for being shed, or sloughed. The snake begins the shedding process by rubbing its nose against rocks or other hard objects to separate the old layer from its lips. After the old layer is loosened, the snake crawls out of its old skin, typically shedding it in a single piece.

Skeleton

A snake’s skeleton is lightweight and highly flexible. Like other reptiles, as well as fish, amphibians, birds, and mammals, snakes are vertebrates—that is, they have a backbone made of small, interconnecting bones called vertebrae. Snakes have an especially large number of vertebrae—all snakes have at least 100 vertebrae, and some species have more than 400. By comparison, humans have just 32 vertebrae. Unlike other vertebrates, the ribs of snakes are not anchored in place by a breastbone, or sternum. Instead, each rib is connected to vertebrae and other ribs by elastic muscles. This makes it possible for a snake to greatly expand its ribcage to pass whole, large prey animals through its digestive tract. These sinuous connections also enable snakes to coil up into compact balls.

Snake skull anatomy shows similar modifications. The bones that make up a snake’s jaws are not rigidly attached to its skull. Instead, they are linked to the rest of the skull and to one another by muscles and stretchy tissues called ligaments. Ligaments also join the two halves of the lower jaw, enabling them to stretch far apart. This flexibility is what makes it possible for a snake to eat animals that are much larger than its head. When swallowing prey, a snake advances its jaws stepwise over the animal by anchoring the teeth from one jaw segment into the prey and then slowly moving the other parts of the jaws forward along the prey.

Windows Live® Search Results

Introduction

Physical Characteristics

Skin

Skeleton