All about snakes

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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 because a snake’s primary method of confrontation is to avoid it. Unless you scare one by grabbing at or cornering it, it’ll leave you alone.

Jump down to: Background  •  Physical description  •  Tongue, Jaws, Fangs, Venom  •  Skin  •  Hibernation (Brumation) •  Movement  •  Reproduction, Lifespan  •  Habitat, Foods, Digestion  •  Predators

When we can set aside our fears, we find that snakes are fascinating creatures that deserve respect for the beneficial animals they are. They help control populations of rodents and other pests in our yards. And snakes themselves are food for other wildlife.

So, what is it that gives us the willies? Nearly everyone—male and female alike—is afraid of them. Is it the unblinking stare? The scaly skin? The long, limbless body? Their slithery means of movement?  Maybe it’s the flicking tongue and sharp fangs. Whichever, Dutch Bihary, a celebrity body paint artist who’s so masculine and muscular he looks like he could take on a pit of vipers single-handed, says that at the sight of a snake he runs away screaming like a little girl! Of course, he’s exaggerating, but here’s the nitty-gritty: Little girls don’t scream and run! We might think our fear is inherent, but studies show that neither girls nor boys have a fear of snakes—they learn it from adults

Five young children holding a long snake.

(© Seth LaGrange / Shutterstock)



Not that there should be, but is there anything about humans that snakes can relate to, and vice versa? Not much. Pets recognize their owners and show a preference for being handled by them rather than strangers. (Snakes in petting exhibits must be “socialized” to tolerate handling by strangers.) Some owners believe their pets like being stroked. (Don’t try this in your backyard!)

Background

Fossil evidence indicates that snakes date back about 120 million years, to the Cretaceous Period when the world was relatively warm. Scientists believe they evolved from lizards. But, lizards have legs, and scientists don’t know why snakes lost their own. There are other anatomical similarities, though, that tie the two groups together, including eyes without lids and no external ears.

Both belong to the scientific class Reptilia and the order, Squamata. From there snakes split away from lizards into their own suborder, Serpentes.

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

Physical description

Snakes range in length from that of the Green Anaconda, Eunectes murinus, native to South America, which can be almost 19 feet long (6 m), way, way down to a 2008 discovery, the Barbados Threadsnake, Leptotyphlops carlae, only about 4 inches (10 cm) long. The weight between species varies wildly, from 0.03 ounces (0.9 gm) up to 500 pounds (227 kg) or more. In the United States, snakes generally range between 8 inches (20 cm) and 8 feet (2.4 m) long. That doesn’t include two non-native species that have invaded Florida: the Green Anaconda and the Burmese Python, Python bivittatus, a native of South and Southeast Asia that grows up to 18 feet.

Like so many other variables about them, skin color differs, too. Snakes may be a uniform color, dull or bright, or have subtle markings. Some have colorful patterns of spots, bands, blotches or stripes. Between sexes, the skin color remains the same and you can’t tell them apart.

Color drawing snake anatomy with labels.

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

Head

Their head has two eyes, located on the sides, a nose with two nostrils, a mouth with a forked tongue, fangs for most, and, for some, a unique set of sensory organs. The brain is small for the size of the body, but studies have shown that captive-bred corn snakes, Elaphe guttata guttata, are capable of being taught how to find their way out of a confined area and remember the cues for doing it again and again.

Eyes

The disconcerting stare that snakes give us? It results from their having no eyelids. In many mammals, including humans, an unblinking stare is menacing, a sign of aggression, but snakes just can’t help it. Also, their eyes fit tightly in their head and have limited movement. A transparent membrane called a brille protects their eyeballs.

Most snakes have round pupils. But, a group of venomous snakes known as pit vipers, have eyes that are vertical and elliptical, which gives them an alien appearance. It’s one way to distinguish non-venomous from venomous snakes, with one exception: the various coral snakes.

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 a pit on the side of its head. They rarely bite, and it’s rarely fatal. (© Paul Wolf/Dreamstime)

Close up of the head of an Eastern Coral Snake, showing its round pupils.

An Eastern Coral Snake, Micrurus fulvius. Unlike other venomous snakes, they have round pupils. They aren’t aggressive and rarely bite, but keep away. (© Jay Ondreicka/Shutterstock)



Snakes don’t see color. And, except for some that hunt using their eyesight, their vision is unremarkable. That is, except for these two groups:

  • Pit vipers: Nocturnal venomous snakes that belong to the family Viperidae. They have a large, unique heat-sensitive depression between the eye and nostril on each side of their head called a pit organ, which gives them a second way of “seeing.” The pit organs are sensitive to infrared thermal radiation—the heat given off by other animals. The snakes can detect the tiniest changes in temperature, which gives them an edge when hunting for prey in total darkness. A pit organ can be easily seen in the two photos above.
  • Boas and pythons: Non-venomous and in the family Boidae. They have smaller pits located in or between the scales that line their upper and sometimes lower lip, usually three or more.

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 which detects ground vibrations. It can also pick up sound waves transmitted through the air, but they probably don’t hear these sounds as well as a human can.

Nose

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

Tongue

You already know that snakes have a forked tongue and they like to flick it fast and repeatedly. It’s like a reptilian challenge, and they’re ready to take us on! Dukes up! But, in reality—get this—they’re tasting us!

Garter snake with forked tongue sticking out.

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

 

The “threatening” tongue is simply collecting samples of chemical molecules in the surrounding air for delivery to the vomeronasal organ, or “Jacobson’s organ,” where it’s located on the roof of the mouth, where a human’s soft palate would be. It’s unique to reptiles.

It’s all rather fascinating, really. Here’s what goes on: The snake flicks its tongue out through its “lips” and wildly waves it around in the air to catch microscopic particles in receptors on its tongue. It then draws in its tongue and deposits those particles into the Jacobson’s organ, where they are sorted by chemical type and analyzed. Each receptor is specialized to receive a specific type of chemical. It’s like a mini-lab in there! 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 one, we’re a perceived change and the tongue shifts into overdrive.

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

Snakes have tiny teeth, but they’re used only to hold onto animals. They aren’t needed for chewing, because snakes swallow their prey whole. Even prey that’s bigger than a snake’s head.

Indian Python with large mouth wide open as it yawns.

A yawning Indian Python, Python molurus. (© mamboo / Shutterstock)



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 that 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 a human’s; instead, they’re held in place by muscle. All put together these features allow snakes to open their mouth up to 150 degrees!

Fangs, venom

Fangs are long, sharp, grooved or hollow, teeth at the front or back of the upper jaw, depending on the species. With some, they fold back when not in use.  Most, but not all, snakes have fangs, and only a few are venomous. For example, Florida has fifty native species of snakes, but only six are venomous.

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 and often don’t inject a full amount.  How to keep yard safe from venomous snakes  

Scaly skin

Snakes are covered in scaly skin that’s composed of keratin, the same protein that forms our hair and fingernails. Scales protect from abrasion and dehydration, give snakes their body color, and provide traction for movement. They’re not one-size-fits-all; besides color, there are other differences, as well. Some species have small, soft scales. Some have overlapping ones. Others are keel-shaped and appear rough. Snakes aren’t slimy. They’re very dry, actually, but some species have smooth, shiny scales that give that appearance. Scales on the top and sides are thinner and smaller than those on the bottom.

As a snake grows, its skin doesn’t grow along with it and eventually gets too tight, like our clothes if we gain weight. And, it wears out, so snakes of any age need to shed it periodically. Here’s how they do it:

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 which softens and separates the two. 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. The snake, now with beautiful fresh skin, 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 it visually impaired or even blind for a few days. 

Orange colored snake shedding its skin, which is a transparent gray.

Bush Viper, Atheris squamiger, shedding its skin. A venomous species endemic to west and central Africa. (© Mark Kostich / Shutterstock)

This process, called ecdysis, occurs as often as needed, perhaps 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 it’s cold-blooded, that is, unable to generate body heat (ectothermic). Its body temperature is the same as the surrounding air. So, if it’s 70° F (21° C), that’s what the snake will be. Because we humans have a relatively constant body temperature of around 98.6° F (37° C), a snake will always feel cool to our touch unless it’s been basking in the sun on a 99° F day.

Snakes prefer the mid-80s (26° C), and they regulate their body temperature by moving in and out of the sun. If the weather becomes too hot, they hide out in a cool spot and remain inactive, When the temps start falling at the end of summer, that’s when they’re most likely to be seen because they’re “sunbathing” more to warm up.

Hibernation (brumation)

Although snakes like to be cool, they don’t want to be too cold, so those that live in cold areas brumate in the winter. “Hibernation” is the commonly used term for any animal that sleeps through the winter, but “brumation” is a metabolically different process and the technically correct word for reptiles. In this state, they sleep, but not deeply as in true hibernation, and they occasionally stir. They don’t eat during this time.

Beforehand, they crawl into such places as caves or holes in the ground below the frost line, sometimes in large groups. (Garter snakes, with which most of us are familiar, are relatively cold-hardy and among the last to hibernate in the fall.) Some snakes return to the same den year after year. In the spring, males leave their den first, and the females follow later.

Movement

When we see a snake slithering away, doesn’t it form a familiar S-shape? That’s typical, and to quote poet William Stafford, “When the snake decided to go straight, he didn’t get anywhere.”

That’s pretty funny, but not entirely true because they can use specialized muscles and the scales on their belly to give them traction to move in a straight line, if they really, really want to.

The S-shape is the most common, but there are four methods of movement.

An Eastern Ratsnake, which has black skin, climbing a Silver Maple tree.

Eastern Ratsnake, Pantherophis alleghaniensis, climbing a tree. (Richinpequea / Wikimedia; CC BY-SA 3.0)

Serpentine: The S-shaped movement we usually call “slithering.” The snake accomplishes this by contracting its muscles and thrusting its body side to side. In water, the S-movement is used exclusively. (Note the shape of the snake’s body in the image at the top of this page.)

Rectilinear: This is straightforward movement. The body moves through the action of three sets of muscles, including one within the skin of the belly, that propel it forward. Watch video of this

Sidewinding: The snake contracts its body and then flings it sideways; commonly used in habitats with loose sand, like deserts.

Concertina: A snake can climb by using this method. It moves its head forward, then bunches up the middle and clings tightly while pulling up the tail end. Following that, it springs forward to get a new grip with the front end. And so on.

Reproduction

Mating usually takes place in early spring as temperatures begin to warm, although some snakes mate in the fall. There’s a frenzy of activity as males follow pheromone trails left on the ground by females. Sometimes dozens of males will try to wrap themselves around a single female and form a “mating ball” as they try to be the victorious suitor.

Two Northern Water Snakes lying on ground surrounded by twigs, one loosely wrapped around the other.

Mating Northern Water Snakes, Nerodia sipedon. A non-venomous species. (brunop / Flickr; CC BY 2.0)

In more refined situations, where there’s a single courting couple, a male begins 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 hers and wraps his tail around it. 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 intestinal and urinary matter exit the body, and, also, where copulation occurs.

Anatomically, males are doubly endowed in a way. They have two sex organs, called hemipenes, although only one is used at a time in mating. (They’re hidden away when not in use.) Mating usually takes place once a year. After mating, males leave with the ambition of finding more females before the season is over.

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

Snake hatching. (PublicDomainPictures / Pixabay; PD)



Eggs and live birth

Some snakes are oviparous (egg-laying) and others are viviparous (live birth). The time between mating and laying eggs is normally one to two months, depending on the species. The eggs, leathery-shelled and numbering up to a hundred, are usually laid in early summer, in a spot that will provide protection and moisture. Once laid, the mother gives her eggs no attention—the eggs and new babies are on their own (a few exotic species, like pythons, will guard their eggs for a few days). Some viviparous species produce up to 150 babies.

There’s a name for baby snakes. Newborns (live birth) are called neonates, and newly hatched are called hatchlings. When they get a bit older, the young ones are snakelets.

A snake that will hatch from an egg has a bump on the front of its jaw that curves forward in front of the snout, called an egg tooth. Its edge is flat and very sharp, and when the right time comes, it will be used to slice the shell open. The egg tooth will disappear later on.

New babies range in length from 3 to 17 inches (7.6 to 43 cm), depending on the species. They’re miniature versions of adults and can start hunting immediately. They grow quickly at first, then slow down considerably after maturity. 

Lifespan
Snakes live ten to forty years, depending on the species.

Habitat

There are four types of snakes: arboreal (tree-dwelling), fossorial (burrowing), terrestrial (ground-dwelling), and aquatic. Most are considered terrestrial, even when they spend a lot of time in trees, underground or in water.

Snakes are found nearly 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 like deserts, but a brook or pond with lots of cover around it attracts the most.

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

Food sources

Snakes use hearing, sight, taste, and ground vibrations to locate food. In the case of pit vipers, they also use their infrared, heat-detecting pit organs. Species may use one sense more than others, depending on their lifestyle.

All snakes are carnivores, and they’re doing us a favor when they visit our yards because rodents are high on their list of delicacies. The US Natural Resources Conservation Service says snakes are earth’s “most effective control of the rodent population.”

They also gulp down vast quantities of insects, other reptiles, and just about anything else they can swallow, including a gardener’s pet peeve—slugs. Smaller snakes eat smaller prey. Most eat once a week to once a month. The frequency depends on the availability and size of food. That said, not all snakes eat all things. For instance, some species seek out eggs or snails only. There are others that feed on worms and insects.

Snakes can swim very well and search for some of their prey in or near water. Since their eyes and nose are located at the top of the head, they can see and breathe while swimming.

Digestion

Snakes eat their food whole. Some can eat up to one hundred percent of their body weight in one meal! After a meal, they raise their body temperature to speed up digestion. They make this happen 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 entire body of their prey, including the bones.

Predators
Snakes are prey for birds, skunks, opossums, raccoons, fish, other reptiles, minks, ferrets, and house cats. Humans take a large toll on their populations. Their most significant threat is habitat loss.

Let them flee

Snakes just want to get away from humans and will quickly do it given half a chance. A cornered snake will be frightened and express it by hissing and shaking its tail. (The shaking tail may rustle nearby brush and sound like the rattles of a rattlesnake. Many harmless snakes are killed because of this.) Because it’s trapped, a snake 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. 

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

More reading:

Snakes: frequent questions   
Proper rescue, care for injured or orphaned urban wildlife
For this snake, ‘rough’ takes on new meaning  

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