Reptiles: Snake

Range: every continent except Antarctica Habitat: every habitat, except where it is very cold

SSSensational serpents!

Snakes are one of several groups of reptiles. They have long, slender bodies, no legs, no eyelids, no ears, and are covered with back-folded skin sections called scales. Like other reptiles, they use the heat of the surrounding air to regulate their body temperature. Snakes' flexible bodies allow them to stretch out to warm themselves quickly, curl up to conserve body heat, or just warm a particular part of their bodies. They are found on land and in water, as well as in every habitat imaginable, except where it is very cold.

What's for lunch?

There are almost 3,000 snake species and most are well known for helping control pest populations by eating rodents and rabbits. But snakes are carnivores and will eat any prey item, from tiny ant eggs to an antelope or tapir for the largest species. Some species are very particular, eating only certain foods, while others eat a wide variety of things. Some species of snakes even eat toxic frogs and salamanders without getting sick, and there are other snakes with special adaptations that allow them to eat bird eggs. These snakes swallow the egg whole and crush the shell with special vertebrae or backbones, digesting the liquid of the egg and spitting out the shell.

Grocery shopping

Snakes find their prey in a variety of ways: by sight, by using heat-sensing pits on the sides of their heads (these snakes are called pit vipers) or on the lips, or by sensing vibrations with their bodies. In addition, when a snake flicks its tongue, it is gathering scent particles from the air and bringing them to a special organ, called the Jacobson's organ, inside the mouth. It's a little like "tasting" the air to see what's nearby. Snakes have two main methods of finding food: active hunting for food or sitting and waiting for food to come to them. It's usually the larger snakes, like pythons, boas, and cobras, that use the "sit-and-wait" technique, but even these snakes may have to move to another area from time to time if they are not successful.

What a mouthful!

Can you imagine trying to stuff a whole watermelon in your mouth? Well, snakes can eat prey that is up to 20 percent of their body size! They begin their meal by swallowing prey headfirst, holding on with sharp teeth that point backward. A snake's mouth bones are loosely attached to each other and to the skull, and the lower jaws have a stretchy band of skin holding them together. Next, throat and body muscles help pull the prey into the esophagus. Also, the opening to their windpipe is at the front of their upper mouth and moveable, so that they are able to breathe while they are swallowing. Depending on the size of the meal, a snake may not have to eat again for several weeks or months.

Quick as lightning

Snakes can strike (or reach forward quickly to grab their prey) with amazing speed. Some just snatch small items and begin swallowing immediately, others grip and constrict around their prey, making it harder for their victims to breathe, while venomous snakes inject a toxic substance into their prey that kills or paralyzes it. People often fear snakes for their venom, but only a third of snake species are venomous and deaths from snakebites are very rare.

Do the locomotion

Most people think of "slither" when asked how a snake moves, but for a group of animals with the same basic body structure, different snake species can move in a surprising variety of ways. Even the way that they slither can vary widely. Special flattened scales on the underside of their bodies, called ventral scutes, give them the traction they need to move. Snakes with scutes on just the underside of their bodies tend to move slower; faster snakes have scutes that extend upwards to the sides of the body: the more scutes, the faster the snake. However, sea snakes have flattened tails that they use like paddles to propel them through the water, and some tree snakes are called "flying snakes," although they don't really fly but can flatten their bodies and spread their ribs to glide from tree to tree.

Raising baby

Most species of snakes are oviparous and lay from 2 to16 eggs in a clutch, although some species lay up to 50 or more. The mother snake incubates her eggs by burying them or by wrapping her body around them and "shivering" to generate heat. In some python species and the king cobra Ophiophagus hannah, the mother stays to protect her eggs from anything that would eat them; in other species, the eggs are left to hatch without any care from the parent. Egg-laying snakes are mostly found in tropical and temperate climates.

Some snakes are live bearers, but whether they are viviparous or ovoviviparous is not known for most species. Live-bearing snakes are found in more extreme climates and at higher altitudes where the weather is colder, because the developing young can be kept warm inside the mother's body.

Changing skin

Snakes continue to grow their entire lives, but their outer skin does not, so they need to shed, or molt, their external skin from time to time. About two weeks before it is ready to shed, the snake stops eating and its skin turns dull. To cast off the old skin, the snake may rub its head against a rough surface to help turn the skin inside out, much like you might pull off your socks! Young snakes shed soon after hatching or birth; because they grow quickly at first, they shed several times in the first year. As the snake gets older, it molts less often, perhaps just two to four times per year.

Staying safe

Snakes are not generally aggressive, but they do have to protect themselves from predators. The most common means of defense is camouflage. Most blend into their surroundings while some have evolved to look like another, deadlier snake. For example, some kingsnakes Lampropeltis sp. have coloration that makes them look similar to dangerous coral snakes or pit vipers, although they themselves are actually quite harmless. Snakes can also flee from danger and some may fool a potential predator into thinking they are bigger or more threatening than they really are: cobras rear up and spread skin around the head and neck to create a large hood. Another trick is to open the mouth really wide to show a flash of white or color, which startles the predator and gives the snake the split second that it needs to escape. And, of course, everyone is familiar with the warning sound of the rattlesnake's tail!

S.O.S. (Save Our Snakes)

With snakes so widely distributed around the world, habitat loss and hunting for food or trade in snakeskins can have an impact on their survival. Yet when you consider how quickly rodents and rabbits reproduce, we owe a big thanks to snakes for helping control these populations. And scientists have been researching ways snake venom can be used in human medicine.

Diverse in size and color, with an important role in the web of life, snakes should be appreciated for their beauty and respected as fellow dwellers on this planet. Please leave them be.