Snakes

A cold-blooded animal with a long, cylindrical body and no legs.

What comes to your mind when you think of snakes? Do you picture slimy, scary, slithering creatures? You might be surprised to learn that snakes are not at all slimy and few are dangerous to humans. Although many people fear snakes, the truth is that they are fascinating animals and an important part of Earth's ecosystems. Let's learn more about snakes.

Snakes are long, slender reptiles without arms or legs. There are over 3,500 different kinds of snakes that have been identified. They range in size from 4 inches (10 cm) to more than 30 feet (9 meters) in length. Snakes can be found on every continent except Antarctica. A few islands, including Ireland and New Zealand, have no native snakes. Most snakes live on the ground, but some live in trees, in underground tunnels, or even in the ocean. Snake habitats range from tropical rainforests to grasslands to deserts.

All snakes are vertebrates, which means they have a skeleton with a backbone. Snakes' backbones are long and flexible. Snakes have as many as 200-400 vertebrae and ribs! Their internal organs – throat, stomach, lungs, liver – are elongated to fit into their long, thin body.

A snake's skin is smooth and dry, and made of a variety of sizes of scales. The scales are composed of keratin, the same substance as human fingernails. The scales near the head are small, while the scales on the underside of their body are thick and protect their bodies from the ground. A snake continues to grow throughout its life, but its outer skin does not.

A snake periodically sheds its skin as part of the lifelong process of growing. This action of shedding, which can take several days, is called molting. When the skin and scales are worn out, the old layer begins to loosen near the snake's mouth. The snake scrapes its head against a rough object to break the skin loose. The snake then crawls out of its skin, leaving the discarded skin intact. If you find a snakeskin, you will see a transparent envelope that shows the snake's scale pattern. Although a snake grows and sheds its scales many times throughout its life, the number and pattern of its scales stays the same.

Snakes do not have external ears. They do have an internal sensory ear bone, called the columella, which detects vibrations from the air or ground. Their eyes do not move inside their heads, and they do not have eyelids. Instead, their eyes are covered by transparent scales, so they remain open even in sleep.

Snakes have specialized senses that help them hunt and defend themselves. They use their long, forked tongues to detect smells in order to find food or avoid enemies. When a snake flicks its tongue, it is smelling its environment. The tongue is gathering odors from the air and from whatever it touches. These collected scents then go to special sacs, called Jacobson's organs, at the roof of its mouth. There, the smell is analyzed so the snake receives the message that food or an enemy is near.

Some snakes have a special pit located near their eyes that allows them to detect small changes in temperature. This allows them to be aware of the heat given off by the bodies of rodents or other animals they might want to eat. Such snakes are able to capture prey animals in total darkness by sensing their body heat.

People are often afraid of snakes because some are venomous. (Scientists do not refer to snakes as poisonous.) Venom is a toxic substance that is injected into a victim, primarily for the purpose of securing prey. It is true that many people have been victims of snakebite. However, of all the snakes in the world, only 15% are venomous, with most of those having venom that is dangerous only to their small prey animals. Just 7% are able to significantly wound or kill a human. Snakes prefer to be left alone, and will bite humans only when they are frightened or provoked. Antivenom medicines have greatly reduced the number of people killed by snake bites.

Scientists classify snakes into five main families: Pythons, Boas, Colubrids, Vipers, and Elapids.

Pythons

Pythons, found in Asia, Africa and Australia, are some of the largest and most powerful snakes, including the world's longest snake, the reticulated python which can grow to 33 feet (10 meters) in length.

Boa

Boas are thick, heavy snakes found in Central and South America, including the world's heaviest snake, the anaconda which can weigh more than 500 pounds (250 kg.)

Colubrids

Colubrids are the largest and most varied group of snakes. Three-quarters of the world's snakes, including common garter snakes, belong to this group.

Vipers

Vipers are venomous snakes with triangular-shaped heads and long, hinged fangs. Pit vipers, such as rattlesnakes, have heat-sensitive pits on the front of the face that detect warm-blooded prey animals.

Elapids

Elapids are slender but highly venomous snakes, including black mambas, cobras, coral snakes and the world's most venomous snake, the Australian taipan.

All snakes are carnivorous. That means that they eat other animals. Some snakes are active hunters, while others hide and wait to ambush their prey. Snakes do not have the right kind of teeth to chew their food so they must eat their food whole. The jaws of snakes are not fused to the skull, so the lower jaw can separate from the upper jaw. This allows their mouths to open wider than their own bodies in order to swallow their prey whole. A tube at the bottom of their mouths extends far enough to take in air when their mouths are full of food.

Once swallowed, the muscles of their bodies and their hook-shaped teeth help push the food toward the stomach. The food is then digested over a long period of time, depending upon how warm the snake is. The warmer their bodies, the faster they digest their food. But it generally takes 3–5 days for food to be digested. In very big snakes that eat large prey, digestion can take weeks. Because of this slow digestion process, snakes do not need to eat every day. Depending on their size and diet, they may go for days or weeks, or even months between feedings.

Venomous snakes inject venom into their prey through a pair of hollow fangs in the front of the mouth. This immobilizes their prey and starts the digestive process even before the snake swallows that food. Constrictors, such as nonvenomous pythons and boas, wrap their bodies around their prey and squeeze until their victim stops breathing or its heart stops beating. Then they swallow their prey whole.

Snakes typically eat rats, mice, birds and their eggs, squirrels, lizards, fish, frogs, gophers, and other small rodents. Their digestive organs are highly stretchable to allow for prey much larger than their own bodies. Some smaller snake species consume insects, slugs, or earthworms, and the smallest of all snakes, the 4-inch-long thread snake, eats the eggs of ants and centipedes. Very large snakes, on the other hand, will eat deer, pigs, monkeys, and other large prey. Some snakes, including cobras and kingsnakes, eat other snakes, including venomous snakes like rattlesnakes and copperheads.

Snakes are an important part of the food web in many ecosystems. As predators, they help control rodent populations, which is important because too many rodents can harm plants and destroy crops. When humans attempt to eliminate snakes in a certain region, the result is usually an unwanted increase in rodent populations. Snakes also provide food for other animals as they are the natural prey of hawks, owls, foxes, turtles, coyotes, opossums, and raccoons. Snakes have an important role in the balance of nature.

People, other mammals, and birds are known as warm-blooded or endothermic animals. Our bodies can regulate our temperature internally as needed for our environment. We sweat when we are hot and shiver when we are cold.

Amphibians and reptiles are cold-blooded, or ectothermic. Their body temperatures match that of their surroundings. Because of this, cold-blooded animals cannot survive well in extreme heat or cold. To warm themselves, they will move to a sunny rock or roadside. To cool their bodies, they will seek shade or sometimes even dig a hole in the ground.

The bodies of snakes have no legs, feet, or flippers to propel them along. They must use the action of their scales and muscles to move their bodies across the ground. The scales on the underside of their bodies are specialized for this purpose like the tread on a tire.

Depending on the type of snake and the environment, snakes use one of four methods of movement: serpentine, sidewinding, concertina and rectilinear.

• Serpentine motion, also known as lateral undulation, is the side-to-side, S-shaped movement used by most snakes. In most cases, the snake pushes off firm objects on the surface, such as rocks or twigs, and uses its scales and muscles to thrust itself forward and bend its body to the left and right, creating a series of curves.
• Sidewinding motion is used in environments that lack anything firm to push against, such as sand or slick mud. Sidewinders contract their muscles and fling their bodies, using only two points of contact with the ground. The snake appears to be rolling in a lateral motion rather than straight ahead.
• Concertina movement, sometimes called accordion motion, is especially useful for climbing and in tight spaces such as tunnels that do not have room for side-to-side movement. The snake anchors the front of its body, bunches up the middle of its body into tight curves, and pulls the back forward, much like an inchworm.
• Rectilinear movement, also known as caterpillar movement, is a slow, creeping, straight-line motion. The snake uses scales on its belly to grip the ground while pushing forward. This silent motion is often used by large snakes stalking prey.

See how snakes use these four styles of movement in this video and diagram from How Stuff Works.

Flying snakes may sound like a myth, but some snakes do hang from branches and swing themselves into the air. By flattening their ribcage and making a side to side motion, they keep their bodies in the air long enough to glide for about 300 feet (100 meters) before landing on the ground or another tree. All flying snakes are venomous and live in the tropical rainforests of Sri Lanka and Southeast Asia. No snakes can fly upwards or take off from the ground.

Many species of snakes can move well in water. Some just slide on the surface, while others can actually swim underwater. The heaviest snake in the world, the anaconda, lives in slow-moving South American rivers and swamps. Its eyes and nostrils are located on the top of its head so it can see and breathe while the rest of its body is hidden underwater. Sea snakes live the majority of their lives in the ocean, feeding on fish and eels. They do come to the surface to breathe air, but can often stay underwater for an hour or more. Aquatic snakes use serpentine motion to propel themselves through the water.

The type of teeth a snake has is dependent upon how the species catches food. All nonvenomous snakes have teeth on the upper jaw and the lower jaw. A snake can often grow more teeth as needed because teeth are sometimes lost while feeding. It is possible for a snake to grow and use many sets of teeth over the course of its lifetime. The teeth are hook-shaped and curve backward toward the throat, to keep prey from escaping the snake's mouth.

Venomous snakes have either grooved or hollow fangs. The venom, which comes from glands located under each eye, flows down the groove or through the hollow portion of the fangs and is injected into the prey. In vipers like rattlesnakes, the fangs are retractable: they fold up against the roof of the mouth when the mouth is closed. When striking, the fangs come down to inject the venom. Some vipers' fangs can grow to be two inches long!

Female snakes produce young about twice per year. Most snakes lay eggs, but in some species, the babies are born alive. In a strange combination of the two, some snakes have eggs that stay inside their bodies until the eggs hatch and then the babies are born live. Snakes can have anywhere from one to 150 baby snakes at a time. Baby snakes look very much like their parents, only smaller.

Snake eggs are not hard like a chicken egg, but are leather-like and can be torn open by the baby snake from the inside with a special “egg tooth” that the snake will lose soon after hatching.

Most snakes do not take care of their offspring, but a few species will protect the eggs and then the new babies for a short time after they have hatched. Snakes reach maturity within two to four years and can live as long as 25-30 years. However, natural predators and human activity often limit snakes' lifespan in the wild.

The coloring of snakes can offer protection from predators in different ways. Some snakes have a camouflage coloring which allows them to blend into their surroundings and keeps their potential prey from spotting them. Many tree-dwelling tropical snakes are bright green and look like vines. Other woodland snakes have a brown coloring that match the pattern of dead leaves on the forest floor. Snakes in rocky or desert locations often have pale skin patterns that blend in with gravel or sand.

Some snakes have coloring or behaviors which mimic another snake for the purpose of confusing predators. For example, in North America, the harmless kingsnake has bright red and black rings, similar to the venomous coral snake. The kingsnake's resemblance to a dangerous snake warns potential enemies to stay away. Fox snakes and gopher snakes, when threatened, may rapidly shake the end of their tails. If the tail contacts dry leaves, it sounds like the rattle of a rattlesnake.

Snakes warn predators away in various ways. Some snakes inflate part of their bodies or rise up and spread their neck regions to look menacing. Others give off a bad smell, make hissing sounds, or rattle their scales. Hognose snakes play dead, rolling onto their backs and letting their tongues hang out. In all cases, the snake is trying to avoid contact with an animal or human it perceives as dangerous. A snake's first defense is to move away or escape from a possible threat.

Snakes that live in cold climates must find shelter from winter temperatures by burrowing into holes, tunnels, tree stumps or caves. Some snakes hibernate in communal dens with other snakes of different species. Their bodies are not really asleep, but in a special condition that makes them appear as if they are dead to people who are not aware. This state of inactivity is called brumation. During this time, which can last up to seven months, snakes eat very little and move and breathe very slowly. If there is a warm day during the winter, they may emerge to bask in the sun and then return to sleep. In the spring, snakes can sense when the air is warming and return to normal activity.

The largest gathering of snakes in the world is in the Narcisse Snake Dens in Manitoba, Canada, where tens of thousands of red-sided garter snakes awake from hibernation. Each spring, crowds of people visit to see the snakes emerge from their winter dens.

Idaho is home to 12 species of snakes:

• Rubber Boa
• North American Racer
• Ringneck Snake
• Desert Nightshade Snake
• Striped Whipsnake
• Gophersnake
• Long-nosed Snake
• Western Ground Snake
• Common Gartersnake
• Western Terrestrial Garter
• Prairie Rattlesnake
• Western Rattlesnake

All of Idaho's snake species are nonvenomous except for the two rattlesnake species. The four most common snakes in Idaho are the gopher snake, Western rattlesnake, terrestrial garter snake, and North American racer. Visit Reptiles of Idaho at Idaho State University to learn more about each of the above species.

There are about 130 species of snakes in the United States. Of these, only 22 species are venomous: the copperhead, the cottonmouth/water moccasin, three kinds of coral snakes, and 17 kinds of rattlesnakes. Copperheads are found in the eastern United States, cottonmouths in wetlands of the southeast, coral snakes in the southeast and southwest, and rattlesnakes in almost all states. Copperheads, cottonmouths, and rattlesnakes are pit vipers, while coral snakes are elapids. The bite of any of these venomous snakes can be dangerous, so anyone who is bitten by one should seek medical attention quickly.

There are a number of different rattlesnake species in North America. Different species of rattlers live in different habitats, including forests, grassland, wetland, brush, and desert. They are known for their rattles, a series of interlocking hollow scales, found at the tip of the tail. A new segment is added to the rattle every time the snake sheds its skin. When a rattlesnake is threatened, muscle contractions cause the scales to click together, warning predators to stay away. Baby rattlesnakes cannot rattle until they have shed their skin at least once, but they can still inject venom when they bite. The Western Diamondback rattlesnake, well-known for its diamond-shaped design along its back, is responsible for the highest number of snake bites in the United States.

The cobra is well known for its hood that it puffs out when in a defensive stance. When in a threat display, it can raise the front of its body 3-4 feet off the ground and pursue its enemy in this position. Cobras are the world's longest venomous snake and are found in the Philippines, India, southern Asia, and Indonesia. They eat birds, small mammals, and other snakes. The cobra's bite has enough venom to kill an elephant. Some cobras can even spit venom up to 6 feet away. The study of cobra venom has led to the development of pain relievers and cancer medicines for humans.

Boa constrictors, nonvenomous snakes found in Central and South America, loop their coils around their prey and squeeze in order to suffocate the animal and stop blood flow. By this method, they may kill their victim before eating it whole. They tend to ambush their prey, often by hanging from trees and dropping down on unsuspecting monkeys, rodents, or deer. Most boa constrictors live in caves or other cool places but have been known to find themselves in cities as people expand into their habitat by building homes and farms.

Anacondas have been the topic of many scary movies which portray them as aggressive snakes that attack people. But the truth is that they like to be alone and are often difficult for scientists to study because they are hard to locate. They live in or near rivers in South America and primarily eat amphibians, birds, and fish, but sometimes larger prey such as jaguars and deer. They can grow to be 30 feet long (9 meters) and 12 inches (30 cm) wide.

Burmese pythons, native to Southeast Asia, are huge constrictor snakes that can grow to 20 feet in length. Unfortunately, about 30 years ago these pythons were introduced into the swamps of the Florida Everglades in the United States. Today there are tens of thousands of invasive Burmese pythons in the area, and because they do not belong in the Everglades ecosystem, they have caused significant damage to the native populations of mammals and birds.

Being cautious about snakes can be important since it helps us be aware of our surroundings when we're passing through territory that might have dangerous snakes. But people also sometimes believe “facts” that aren't true about things they fear. Here are some invented myths about snakes:

MYTH	FACT
Snakes must be coiled up to strike.	A snake only coils as a defense mechanism and to see more clearly. They do not have to be coiled when they strike. They strike quickly and can reach a victim at a distance nearly equal to the length of the snake's body.
Snakes are mean.	A snake lives in a world where they must defend themselves. They are not out to get people. They are just defending themselves because a human is so much larger than they are.
Rattlesnakes always rattle before they strike.	A rattlesnake rattles to warn if they are afraid they have been seen, but studies show that if they are camouflaged, they might not rattle.
Only venomous snakes bite.	Any snake can bite when threatened, and although the bite of a nonvenomous snake has no venom, it can be painful and possibly cause infection.
The number of rattles on a rattlesnake tells the age in years.	A rattlesnake can shed its skin several times per year, so although this does create a new rattle with each shedding, it is not representative of a year's time period. Older rattlesnakes can also lose rattles in battle or while hunting food.
Snakes make good pets.	Gentle species such as corn snakes, king snakes, and smaller ball pythons can make good pets if given the proper care. But too often, snake owners find that they have made a mistake as their snakes grow bigger than expected. Pet snakes can be a 20-year commitment. Anyone who is considering having a snake for a pet needs to learn as much as they can about the snake's needs before making that decision.