All about snakes

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Jump down to:  Physical description  •  Reproduction •  Habitat / Food sources / Predators

Don’t kill it! In a thriving backyard wildlife habitat expect snakes to be around. You’ll likely never see them, but if you do, it’ll be only for a moment or two, They’ll be just as startled at coming face to face with you. Let them slither away, which they’ll quickly do if you let them. A snake’s primary method of confrontation is: avoid it. Unless you scare them by grabbing at or cornering them, they’re peaceful animals. When we can set aside our fears, we find that snakes are fascinating creatures that deserve respect as an important part of wildlife habitat. They help keep populations of rodents and other pests in our yards under control. And snakes themselves are food for numerous other animals.

Four young children holding a long snake.

Studies have shown that children don’t instinctively fear snakes. (Bill Butcher, USFWS; cc by 2.0)



So, what is it about snakes that gives us the willies? Nearly everyone, male and female alike, is afraid of them (called ophidiophobia). Is it the unblinking stare? The scaly skin? The long, limbless body? Their method of movement? Or, maybe it’s the flicking tongue and sharp fangs, so dangerous-looking. It’s probably all of that. We might think our fear is instinctive, but studies show that children have no fear of snakes; they learn it from adults.

Snakes, so hard for humans to relate to, do have a “soft” side. They aren’t smarter than they need to be for own survival, but owners of pet snakes say their snakes recognize them and show a preference for being handled by them, but not by strangers. Some owners believe their snake enjoys being stroked. Snakes in petting exhibits have even been “socialized” and will accept handling and stroking by strangers. (Don’t try this in your backyard!)

Snakes are members of the reptile family. They belong to the same order, Squamata, as lizards, but to a different suborder. It’s believed they evolved from lizards, although lizards have legs and snakes do not. Snakes don’t preserve well, and fossil evidence is relatively scarce, so scientists don’t yet know why snakes lost their legs, but other anatomical similarities to lizards, including eyes without lids and no external ears is convincing. Besides that, some snakes still have tiny, useless limbs. Fossil evidence so far indicates that snakes date back about 120 million years, to the Cretaceous Period when the world was relatively warm.

Snakes are found in all parts of the world, except Antarctica. There are about 2,700 species. Around 120 of them inhabit North America, including 20 venomous species. 

Physical description
Snakes range in length from that of the Anaconda and Python, which are 25 to 30 feet long, way, way down to a 2008 discovery in Barbados that’s only about 4 inches long (the Barbados Threadsnake, Leptotyphlops carlae). The weight range for snakes runs from 0.002 pounds (0.9 gm) up to 500 pounds (227 kg) or more (the Anacondas). U.S. snakes generally range between 8 inches (20 cm) and 6 feet (1.8 m). 

The coloration of snakes is highly varied and serves to protect them. As with other animals, their color and pattern are designed to blend into their surroundings, to fool the eye of predators. They may be a uniform color, dull or bright, or have subtle markings. Some have colorful patterns of spots, bands, blotches or stripes. Others have a head that’s different in color from the rest of their body. With some, the color changes between the head and the tail.

Eyes: Snakes don’t have eyelids. This missing feature is what gives them the stare we find so disconcerting. In many mammals, including humans, an unblinking stare is menacing, a sign of aggression, but snakes can’t help it. Their eyes fit tightly in their head and have limited movement. A transparent membrane called a brille protects their eyeball.

The pupils of pit vipers, a group of venomous snakes, are vertical and elliptical, which adds to their alien appearance. The pupils of other snakes are round, like a human’s. In the U.S., that’s one way to distinguish a non-venomous from a venomous snake, with one exception: the venomous Coral Snake.)

Side view of a Copperhead snake showing an eye and the pit on its face.

Like most pit vipers, the Copperhead (Agkistrodon contortrix) has vertical pupils and “pits” on the side of their face. (© Paul Wolf)

Snakes don’t see color. And, except for some species that hunt using their sight, a snake’s vision is unremarkable. Pit vipers use special organs (seen as indentations, or “pits,” between the eye and nostril on each side of their face) to help them “see.” The pit organs sense infrared thermal radiation — the heat coming from another animal. This gives them vision of a different sort and is especially helpful to these mostly nocturnal snakes.

Ears: Snakes don’t have external ears. They also lack an eardrum and some of the other internal structures common to mammals. Instead, they have a small ear bone called the columella. Ground vibrations are transmitted to the columella through skin, bone and muscle, delivering a sound pattern. Snakes also pick up sound waves through the air, but they probably don’t hear these sounds, as well as a human, does.

Nose: Snakes have a nose and nostrils they draw air through. It’s their primary method of detecting smells, but not their only one.

Garter snake with forked tongue sticking out.

Garter snake. Notice its forked tongue. (Fritz Flohr Reynolds / Flickr; cc by-sa 3.0)

Tongue: Snakes have what’s called a forked tongue, which means it’s split into two separate pointy tips. They seem to flick their tongue all the time. It certainly looks threatening, but they’re using it to “taste” their environment, including us if we’re nearby. 

They use their tongue to sample chemical molecules in the air which they draw into their mouth for identification by an organ named the vomeronasal organ, or “Jacobson’s organ.” Unique to reptiles, the Jacobson’s organ is located on the roof of the snake’s mouth, where a human’s soft palate would be. This organ has chemical receptors that are each specialized to receive only a specific type of chemical.

Here’s what goes on: The snake flicks its tongue out through its “lips” and waves it around in the air to catch microscopic particles in receptors that are on its tongue. It then draws its tongue into its mouth and deposits the trapped particles into the Jacobson’s organ, where they are sorted by chemical type and analyzed. While this is going on, the tongue is already back outside grabbing more particles. The amount of tongue-flicking is directly related to changes in the snake’s environment. When we approach a snake, we are a perceived change, and its tongue goes wild.

Color illustration of a snake's head, showing Jacobson's organ.

Jacobson’s organ. (Fred the Oyster / Wiki; GDFL 1.2)

The results of the chemical analysis are transmitted to the brain, along with other information gathered by infrared sensors located on the snake’s face. The snake arrives at an answer: Yummy, a big, fat rat is right over there! Or, eek! It’s a human!

Jaws: All snakes have tiny teeth, which are used to hold onto prey, rather than for chewing. Snakes can swallow animals that are wider than their own head. A unique set of jaws makes this possible: Where a human’s upper jaw is fused to the skull, a snake’s is not. Instead, it’s held in place by muscles, ligaments and tendons, which give it a lot of mobility in all directions. The lower jaw is double-jointed, allowing it to dislocate when necessary. And, finally, the bones on the front of a snake’s lower jaw aren’t fused into a “chin,” like that of a human; instead, they’re held in place by muscle. All put together; these features allow snakes to open their mouth up to 150 degrees.

Fangs: Not all snakes have fangs. Most do, but even then only a relative few are venomous and, therefore, dangerous to humans. (For example, Florida has 50 native species of snakes, but only six are venomous.) Fangs are long, sharp, grooved or hollow teeth at the front or back of the upper jaw, depending on the species. Venom is a toxin that immobilizes prey. It originates in a gland located under each eye and flows via a duct through the fangs and into the body of the prey when the snake strikes it. Snakes can control the amount of venom they use. Some snakes have fangs that fold back when not in use. If venomous snakes inhabit your neighborhood, follow these tips:  Keep yard safe from venomous snakes

Color drawing snake anatomy with labels.

Snake anatomy. (Uwe Gille; cc by-sa 3.0)

Scaly skin: Snakes have scaly skin designed to camouflage them, as well as provide gripping power for holding prey. Their skin is made of keratin, the same stuff that makes up our fingernails and hair. There’s a wide variety of types: Some species have small, soft scales. Some have overlapping scales. Others are keel-shaped and appear rough. Scales aren’t slimy, but some snakes have smooth, shiny ones that look that way. Others have little shine or none at all. 

As a snake grows, its skin doesn’t grow along with it and eventually gets too tight. Skin wears out, too, like old clothing, so snakes of any age need to shed their skin periodically. Here’s how it’s done.

The snake moves to a safe hiding place and stops eating. Its body secretes a fluid between a layer of inner skin and the outer skin that softens and separates them. The snake sheds its old outer skin all in one piece by first rubbing its head against a rough surface to make it peel. Then it spends up to several hours crawling forward out of the skin, leaving it inside out, like a dirty sock laying on the floor. The snake now has beautiful new skin, but it will remain hidden for a while longer. That’s because the brille (the transparent protective skin that protects the snake’s eyes) sheds along with the rest of the skin, leaving the snake visually impaired or even blind for a few days. 

This process, called molting (ecdysis), occurs as often as needed, perhaps as often as every three weeks or as long as once or twice a year. The faster the snake is growing, the more often it sheds its skin. Snakes never entirely stop growing.

Cold-blooded: Touch a snake, and it’ll feel cool. That’s because snakes are cold-blooded: They’re unable to generate body heat (ectothermic), and their body temperature is the same as the air surrounding them. If the air around it is 40 degrees, it’ll be 40 degrees, too. We humans have a relatively constant body temperature of around 98.6 °F, so a snake will always feel cool to our touch unless it’s been basking in the sun on a 99 °F (37 °C) day. And, that’s not likely: They prefer temperatures in the mid-80s (26.6 °C). In hot weather snakes are inactive, hiding out where they can stay cool. They regulate their body temperature by moving in and out of the sun. When the temperatures start falling at the end of summer, snakes become more visible, spending more time in the sun to warm up. This is when they’re most likely to be seen by us.

Hibernation: Snakes also don’t like to be too cold, so they hibernate in the winter. They crawl into such places as caves or holes in the ground below the frost line, sometimes in large groups. While hibernating, they don’t eat, and they move very little. Some snakes return to the same den year after year. In spring, males leave their den first and the females follow later. Garter snakes, which most of us are familiar with, are relatively cold-hardy and among the last snakes to hibernate in the fall.

Movement: Snakes have four main methods of moving. The S-shaped, “serpentine” movement is the most common. The snake accomplishes this by contracting its muscles and thrusting its body side-to-side. It moves forward by pushing against resistance points, such as rocks and branches. In water, the S-movement easily moves the snake forward (note the curves of the snake’s body in the image at the top of this page.) Watch video of snake locomotion

Snakes can also propel themselves by creating a rippling movement, something like a caterpillar uses. Another method is “sidewinding,” where it contracts its body and then flings it. Snakes can climb by first extending their head and front of their body. Then they bunch up and cling tightly with the middle part while pulling up the tail end. After that, they spring forward to get a new grip with the front end. And so on. Some venomous Southeast Asian species can flatten their body and “fly” by flinging themselves from high tree branches and gliding.

Reproduction
Mating usually takes place in early spring when temperatures begin to warm up, although some snakes mate in the fall. A female lets males know she’s ready to mate by releasing chemicals from glands in her skin. Called pheromones, they leave a scent on the ground as she moves around. Males follow it until they catch up with her.

A male begins courting by crawling all over the female and bumping his head on the back of her head or flicking her body with his tongue. He aligns his body with her’s and wraps his tail around her. When she’s ready to accept him, the female raises her tail to expose her cloaca (klo-A-kuh), which is a multipurpose posterior opening through which the intestinal, urinary and genital ducts empty. And, in this situation, it’s the receptacle for his penis. Mating commences, and semen enters the female’s body. Males are doubly endowed. That’s to say that they have two penises, called hemipenes, which are hidden away when not in use. Mating usually takes place only once a year. After mating, the males go their own way.

The face of a baby snake can be seen as it begins hatching from its egg.

Snake hatching. (PublicDomainPictures / Pixabay; PD)



The time between mating and laying eggs is normally one to two months, depending on the species. Leathery-shelled eggs (up to 100) are usually laid in early summer, in a spot that will provide protection and moisture: under rocks, in leaves, under debris. Once laid, the mother gives her eggs no attention; the eggs and babies are on their own (a few exotic species, like Pythons, will guard their eggs for a few days.) The babies have a sharp bump on their snout, called an egg tooth. They use it to slice their way out of the shell. The egg tooth disappears later on. Some snakes give birth to live young (up to 150 at a time). Newborns range in length from 3 to 17 inches (7 to 43 cm).

The babies are miniature versions of the adults and can start hunting immediately. Males and females look alike throughout their lives. They grow quickly at first, then slow down considerably after maturity. 

Lifespan
Snakes live 10 to 40 years, depending on the species.

A mass of Red-sided Garter Snakes, Thamnophis sirtalis infernalis, laying on a pile of large stones.

Red-sided garter snakes, Thamnophis sirtalis infernalis, outside their den. (Greg Schechter / Flickr; cc by 2.0)

Habitat
Snakes live everywhere: parks, meadows, woodlands, mountains, grasslands, swamps, marshes, deserts and urban yards. They like a warm climate and prefer temperatures no lower than about 65 °F (18 °C). Some are desert species, but a brook or pond with lots of cover around it will probably attract the highest number of species.

All snakes can swim very well and search for some of their prey in or near water. (A snake’s eyes and nose are located on the top of the head, which allows it to see and breathe while swimming.) Snakes come in four types: arboreal (tree-dwelling), fossorial (burrowing), terrestrial (ground-dwelling), and aquatic. The snakes living in your yard will most likely be terrestrial. Most snakes are considered terrestrial, even when they spend a lot of time in trees, underground and in water.

In urban areas, snakes hide out in untrimmed shrubs, woodpiles, debris piles, in rock piles, under deep mulch, under porches and sheds, in crawlspaces, in basements with a rodent problem. In summer, snakes seek cool, moist places. In winter, they seek warmth and hibernate below the freeze line.

Food sources
All snakes are carnivores, and they’re doing us a favor when they visit our yard: Rodents are high on their list of delicacies. In fact, the U.S. Natural Resources Conservation Service says snakes are earth’s “most effective control of the rodent population.” Snakes also gulp down vast quantities of insects, other reptiles, just about anything else they can swallow, and depending on your gardening pet peeves, including slugs. Most eat once a week to once a month. The frequency depends on the availability and size of food. Not all snakes eat all things. Some species seek out eggs or snails only. Others feed on worms and insects. Smaller snakes eat smaller prey.

Snakes use their hearing, sight and Jacobson’s organ to locate prey. In the case of pit vipers, they also use their infrared, heat-detecting ability. Some species use one sense more than others, depending on their lifestyle. Snakes eat their food whole. Some can eat up to 100 percent of their body weight in one meal. After a meal, they raise their body temperature to speed up digestion. They do it by sunbathing, lying under a warm rock, or even by extending into the sun only their body section that contains the digesting prey while staying otherwise hidden.

Snakes have potent digestive enzymes capable of breaking down the bodies of prey, including their bones. Some snakes, like boas, suffocate their prey by wrapping their body tightly around it. Venomous snakes bite their prey to paralyze or kill them before eating.

Snake behavior when cornered
Snakes just want to get away from humans and will quickly do so, if given a chance. A cornered snake will be frightened and express it by hissing and shaking its tail. Because it’s trapped, it may advance as a bluff to try to scare the individual away. If that fails, it may eventually strike. A snake can strike forward about half the length of its body. 

Predators
Birds, birds of prey, skunks, opossums, raccoons, fish, other reptiles, minks, ferrets, house cats. The most significant threat to snakes is habitat loss and killing by humans.

*Top photo: Red-sided Garter Snake (Thamnophis sirtalis parietalis), widely distributed and harmless. (Tara Allison / WelcomeWildlife.com; cc by-nc 3.0)

More reading:

Snakes: frequent questions   
Proper rescue, care for injured or orphaned urban wildlife  

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