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Snakes: Love 'Em or Leave 'Em?

Ophidiophobia is an irrational fear of snakes. Many people, perhaps a majority, claim to have a loathing or dislike of these limbless reptiles. Why do snakes get such a bad rap? A recent scientific study has concluded that the fear of snakes is evolutionary, passed through the mammalian tree since the first mammals lived in a world dominated by reptiles. This may be true, but in most of the world today, a fear of snakes is out of proportion to the danger that snakes pose to humans.

Snakes lack limbs, eyelids, and ears. They are covered in scales, sport forked tongues, and have the flexibility of contortionists. Some people find their looks reason enough to resent having to share the planet with them, while others love everything about these fascinating reptiles. One thing is for sure, snakes excite interest in just about everyone. Here we present some basic facts -- as well as some myths -- about snakes, and then about snake bites.

Snake Basics
Snakes are found on every continent except Antarctica, and in every country except Ireland, Iceland, and New Zealand. (Recent fossil finds show that there were snakes in New Zealand 20 million years ago.) There are about 3,000 snake species worldwide and just under 140 species in the United States and Canada.

Snakes continue to increase in length throughout their lives, but their growth rate slows after they reach maturity. While the world's largest snakes, Anacondas, can reach 25 to 30 feet in length, North America's longest snake on record was an Eastern Indigo Snake that measured 8 feet 7 1/2 inches.

The giant boa constrictors of the American Tropics, including the Anaconda, are among the most feared snakes. There are a couple of species of boas in North America, but these reach only about three feet long. Boas are not the only snakes that kill prey by constriction, however. North America's constrictors include the common and widespread Milk Snake.

Snakes display a full rainbow of colors and patterns; some even have iridescent scales. North American snakes come in blue, red, yellow, orange, and green, as well as more mundane grays, browns, and blacks, and are adorned with spots, bands, stripes, diamonds, and other often beautiful patterns. The Milk Snake and the Common Kingsnake are among the most variable species, with numerous subspecies of varying and bold coloration. Snakes periodically shed their outer layer of skin, usually in one piece. A rattlesnake adds a new segment to its rattle each time it sheds its skin, normally two to four times a year. Several species of birds use shed snake skins in nest-building.

It's What's Inside That Counts
The vertebrate body has evolved differently in snakes than in other reptiles or in mammals, fish, or birds. In snakes the left lung is either very small or is absent altogether. The kidneys are aligned vertically rather than side by side as they are in mammals.

Snakes can swim, climb trees, and burrow underground, and they do all of this without the assistance of arms or legs. A snake can have as many as 400 vertebrae in its spine; humans have 32 to 34. That's one reason why a snake can tightly coil its body and a human can't!

If you get into a staring contest with a snake you are bound to lose, because snakes don't have eyelids and therefore can't blink. A transparent cover protects the eye. Snakes lack ears and don't "hear" sounds but they can sense vibrations on the ground (or tree or water). Snakes also have other ways of making sense of their environment. One way is by flicking the forked tongue in and out. They don't exactly smell with their tongues but they pick up chemicals in the environment with them. An organ inside the mouth interprets the information brought in on the chemicals, alerting the snake to potential prey, a mate, or even just the way home.

Most of North America's venomous (or poisonous) snakes, including rattlesnakes, copperheads, and cottonmouths, are pit vipers. They are named for small craters in the face that detect temperature changes and help the snake detect prey -- or predator. These pits are so sensitive they can register a temperature change of a tiny fraction of a degree.

The Snake in the Garden
Snakes are meat eaters. Among the foods they eat are birds, mammals, lizards, frogs, eggs, insects, spiders, centipedes, and scorpions. Most are useful residents of the backyard, as they eat rodents, slugs, snails, and other creatures that can be garden pests. Blind snakes live in burrows and consume termites. Some snakes even eat other snakes; the Black Snake, for example, preys on Copperheads, and kingsnakes will eat those and rattlers and coral snakes, too.

All snakes swallow their prey whole. A snake's lower jaw unhinges in the front, enabling the snake to fit a prey item, even a large egg, into its mouth. Some snakes kill their prey first, while others eat it alive. Constrictors kill by coiling their body around the victim and squeezing tighter each time the animal draws in a breath. Before long the prey's heart can no longer fill with blood or its lungs with air.

A snake can adjust the position of its respiration tube so that it can still breathe while its mouth and throat are stuffed with food. It takes days to weeks for a snake to digest a meal, depending on the prey's size. Once fed, a snake may not eat again for months. A large Anaconda may eat only once or twice a year.

Myths and Realities
The folklore about snakes is rich and fanciful. Milk Snakes were once thought to suckle vast quantities of milk from cows. Rainbow Snakes (also called Hoop Snakes), it is said, chase people by forming a hoop shape (holding the tail in the mouth) and rolling after them. Coachwhips have been rumored to speed after adversaries and then whip them to death with their tails. Despite the persistence of such myths, snakes do not chase people; most snakes flee people, some stand their ground in an encounter, but none are known to give chase.

Many people are repelled by the idea of numerous snakes writhing around together, and it's true that snakes gather communally. In much of the United States and Canada, snakes hibernate for the winter. Many gather in communal dens often consisting of several different species. A den may contain several hundred snakes; there are reports of 1,000 snakes denning together. In another snake-gathering ritual, some species of snakes form a "breeding ball," in which numerous males coil around a single female and try to mate with her. While these images frighten some people, the truth is that very few people have ever actually witnessed a hibernation den or a breeding ball. These mainly occur off the beaten path of most of us.

Although it may sound like a creature out of the trials of Hercules, the two-headed snake is a rare but real phenomenon. Two-headed snakes form in the same way as human conjoined twins. If the two heads also have separate necks, they may compete with each other for food and fight over which direction to move in. They sometimes even try to eat each other. The San Diego Zoo had a resident two-headed snake named Thelma & Louise who bore 15 offspring -- all one-headed.

Snake Bites
Many people who are afraid of snakes are more specifically afraid of snake bite. Snakes rarely bite people, but when they do it is often in response to being picked up, poked at, or otherwise disturbed. Americans are more likely to die of a bee sting, the flu, bubonic plague, salmonella poisoning, measles, a lightning strike, a heat wave, fire, choking, or slipping in the bathtub than of a snake bite.

The best way to avoid snakebite is to leave snakes alone. Even nonvenomous snakes will bite if harassed. Some will issue a warning rattle by vibrating the tail in dead leaves, others will flatten and expand the neck in imitation of a hooded cobra, and many species will hiss. Rattling, hissing, and other displays are pretty obvious warnings. If you don't back off, a snake behaving in this way may bite in self-defense.

Only about 20 of North America's snake species are venomous. These include rattlesnakes, Copperheads, Cottonmouths, and coral snakes. Different species have different types of venom, some more dangerous than others. These snakes rarely bite people, and even when they do, the vast majority of venomous snake bites are not fatal. Indeed, North America's venomous snakes are estimated to release venom in only about 50 percent of bites on humans. Still, they are not to be messed with, and snakebites are no joke. Medical professionals have reported that 40 to 100 percent of venomous snakebite victims they have treated have been drunk, and the majority of them have been young males. Poor judgment seems to be one of the biggest risk factors for snake bite.

View a ZipGuide to the venomous snakes of your region.

View a field guide to all the snakes of North America.

Read more about how snakes eat.

 

 

 

 

 

2007 eNature.com