All about snakes

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

Don’t kill him! He isn’t your enemy — snakes don’t prey on humans. In a successful 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. Just let them slither away, which they’ll quickly do, if they can. A snake’s major method of confrontation is: avoid it. Unless you scare them by grabbing or cornering them, they’re peaceful animals. When we can set aside our fears, we find that snakes are fascinating creatures who deserve respect as an important part of a successful wildlife habitat.

Common-garter-snake 3

Garter snake. (Jasonjdking; PD)

What is it about snakes that gives us the willies? Nearly everyone, men and women alike, are afraid of them (called ophidiphobic). Is it the unblinking stare? The scaly skin? The long, limbless body? Their method of locomotion? Or, maybe it’s the flicking tongue and sharp fangs, so dangerous looking. Whatever it is, our response almost seems instinctive. Yet, curiously, instinct may have nothing to do with it — some studies show that children have no fear of snakes; they apparently learn it from adults.

Snakes, so hard for humans to relate to, do have a “soft” side. They aren’t especially smart, but snake owners say their snakes clearly recognize them and show a preference for being handled by them, but not by strangers. Some pet 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 own backyard!)

Snakes are members of the reptile family who 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 that look like spurs. Fossil evidence so far indicates that snakes date back about 120 million years. Snakes inhabit temperate and tropical regions and live on every continent, except Antarctica.

There are about 2,700 species of snakes in the world, with about 120 species living in North America. Only 20 are venomous. Venomous or not, a snake only bites when he thinks he’s under attack. Most bites occur to someone who’s trying to kill or catch a one. What should you do if you happen upon a snake? Slowly back away. It’s as simple as that. Even venomous snakes will avoid striking, if possible.

Physical description
Snakes range in length from Anacondas and Pythons, 25 to 30 feet long, 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 up to 500 pounds or more (Anacondas).

U.S. snakes generally range between 8 inches and 6 feet. Their coloration is highly varied and protects them. As with other animals, their color and pattern is designed to blend into their surroundings, to fool the eye of predators. They may be a uniform color, dull or bright and with 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. It’s this missing feature that 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, too. A clear membrane called the brille protects the 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, but with one exception: the venomous Coral Snake.)

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Like most pit vipers, the Copperhead (Agkistrodon contortrix) has vertical pupils. (© Paul Wolf)

Snakes don’t see color. Except for some species who hunt using their sight, a snake’s vision in unremarkable. Pit vipers are equipped with heat-sensing organs (seen as indentations, “pits,” between the eye and nostril on each side of their face) that can locate warm-blooded prey. The pits give them binocular heat-sensing “vision” that’s especially helpful to nocturnal hunters.

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 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.

Forked tongue

All snakes have a forked tongue. (Jon Nelson / Flickr; cc by 2.0)

Tongue: All snakes have a forked tongue, and what’s with all that flicking in and out they do? Well, as it turns out, they’re tasting 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 a special 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 our soft palate would be. This organ has chemical receptors that are each specialized to receive only a specific type of chemical. Essentially this is what the snake is doing with his tongue: He flicks it out through his “lips” and waves it around in the air to catch microscopic particles in receptors that are on his tongue. He then draws his tongue into his mouth and deposits these 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 it, we are a perceived change and his tongue goes wild.

Jacobsons organ

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

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

Teeth: All snakes have tiny teeth, but they’re not designed for chewing. They’re used to hold prey, which is always swallowed whole. Snakes are known for being able to swallow prey that’s sometimes wider than the snake’s own head. What makes this possible is a unique set of jaws. Where a human’s upper jaw is fused to the skull, the snake’s is held in place by muscles, ligaments and tendons that give it a lot of mobility in all directions. In addition, 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 are sharp teeth at the front and back of a snake’s upper jaw. They’re hollow, which allows venom to pass through them when the snake strikes. The venom originates in a gland located under each eye and flows through a duct to the fangs. Venom is used to immobilize prey. Venomous snakes have long, grooved fangs that fold backward when they’re not needed. Non-venomous snakes have stationary fangs.

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Snake anatomy. 1. esophagus 2. trachea 3. tracheal lungs 4. rudimentary left lung 5. right lung 6. heart, 7. liver 8. stomach 9. air sac 10. gall-bladder 11. pancreas 12. spleen,
  13. intestine 14. testicles 15. kidneys
(Uwe Gille/ Wiki; cc by-sa 3.0)

Scaly skin: A snake’s skin is scaly and made of keratin, the same stuff that makes up our fingernails and hair. There’s a wide variety of types: Some species of snakes have small, soft scales. Some have overlapping scales and some scales are keel-shaped and appear rough. Some scales are soft. Some are smooth and shiny and look like they’re slick. But snakes aren’t slimy. Others have little shine or none at all. Snakes have only a single row of scales along their belly. The scales on a snake’s skin help to camouflage him and provide gripping power for holding prey. As a snake grows, his skin doesn’t grow with him. It eventually fits like a constricting girdle, and the skin can wear out, too, like old clothing. So, he gets rid of it. When it’s time, the snake’s body secretes a fluid between layers of skin that softens and separates them. He moves to a safe hiding place and stops eating. The inner surface of the outer skin liquefies, allowing it to separate from the underlying new skin. He sheds his old skin all in one piece by first rubbing his head against a rough surface to make it peel. Then he spends up to several hours crawling forward out of the skin, leaving it inside out, like a dirty sock laying on the floor. The brille sheds, too, leaving the snake visually impaired or even blind for a few days, during which he stays hidden. The snake’s body now has beautiful new skin. 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 he sheds his skin.

Touch a snake and he’ll feel cool. This is because snakes are cold-blooded; they can’t generate body heat (ectothermic). Their body temperature is the same as the temperature surrounding them. If the air around him is 40 degrees, he’ll be 40 degrees, too. Humans have a relatively constant body temperature of around 98.6 degrees, so a snake will always feel cool to our touch, unless he’s been basking in the sun on a 100 degree day. And, that’s not likely: They prefer temperatures in the mid-80s. In hot weather they’re inactive, hiding out where they can stay cool. Snakes regulate their body temperature by moving in and out of 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.

Since snakes also don’t like it to be too cool, in winter they hibernate. They generally crawl into 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. Harmless and common, garter snakes are very cold hardy and among the last snakes to hibernate in the fall. In spring, males leave their den first and the females follow later.

Movement: If a snake is cornered by a human, he’ll become frightened and express it by hissing and shaking his tail. Trapped, he may advance as a bluff to try to scare the individual away. If that fails, he may eventually strike. A snake can strike about half the length of his body. Snakes have four main methods of moving. The S-shaped, “serpentine” movement is the most common. The snake accomplishes this by contracting his muscles and thrusting his body side-to-side. He moves himself 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.)

Snakes can also propel themselves by creating a rippling movement, something like a caterpillar uses. Another method is “sidewinding,” where he contracts his body and then flings it. Snakes 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. Finally they spring forward to get a new grip with the front end. And so forth. Some snakes can “fly” by flinging themselves from high tree branches. They don’t actually fly, they flatten their bodies and glide. They are venomous and, fortunately for us, live far away in Southeast Asia.

Habitat
Snakes live everywhere: parks, meadows, woodlands, mountains, grasslands, swamps, marshes, deserts and urban yards. Snakes like a warm climate and prefer temperatures no lower than about 65 degrees. Some are desert species, but a brook or pond with lots of cover around it will probably attract the greatest number of species. All snakes can swim very well and look 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 him to see and breathe while swimming.) Snakes come in four varieties: arboreal (tree-dwelling), fossorial (burrowing), aquatic and terrestrial (ground-dwelling). 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 huge 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 life style. 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 very powerful 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 him. Venomous snakes bite their prey to paralyze or kill them before eating.

Reproduction
Mating usually takes place in early spring when temperatures begin to warm up, although some 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 about. The males follow it until they catch up with her. A male begins courting by crawling all over her and bumping his chin 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 the posterior opening through which the intestinal, urinary and genital ducts empty. Mating commences and semen enters the female’s body through this opening. Males, uniquely, are doubly endowed. That is to say, they have two penises, called hemipenes, which are hidden when not in use. Mating usually takes place only once a year. After mating, the males go their own way.

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 laid usually 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.) Baby snakes 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) and carry their babies for 3 months or more. There are also some snakes who hold their eggs until they hatch and then deliver live babies. Newborns range in length from 3 to 17 inches. They’re miniature versions of the adults and are able to start hunting immediately. Males and females look alike throughout their lives. The babies grow quickly at first, slowing down considerably after maturity. They never completely stop growing. Snakes live 10 to 40 years, depending on the species.

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

Snakes at a glance

Appearance: Coloration highly varied, incl. stripes, spots, bands.
Size U.S. snakes: 2 in. to 9 feet.
Lifespan: 10 to 40 years.
Range/habitat: Lives anywhere there’s cover and food. Hides in undergrowth, grasses, debris, under rocks, in woodpiles, under shed, in crawlspace. Most often seen in fall.
Behavior: Docile, but will bite if cornered or handled.
Foods: Small mammals, lizards, snakes, toads, frogs, eggs, slugs, worms, fish.
Nest: Hibernates in a den with others through the winter. Emerges in early spring.
Reproduction: Mating in early spring or fall. May be live birth or eggs laid in soft, protective place. Gestation usually 1 – 2 months.
Predators: Birds of prey, other snakes, crows, raccoons, opossums, shrews, foxes, humans.
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: Squamata
Suborder: Serpentes
Family: Over 15 families
Species: Over 2,700
 

*Top photo: Red-sided Garter Snake (Thamnophis sirtalis parietalis). Widely distributed and harmless. (WW)

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