WHY DO ALL REPTILES HAVE TAILS?

by Whit Gibbons

March 7, 2010

The fact that a question was asked by a second-grader does not mean it is uninteresting, nor does it mean the answer is simple.

Q.: Why do all reptiles have tails?

A.: Rudyard Kipling offered fanciful explanations for the how and why of many natural marvels in his "Just-So Stories," but he did not address the issue of why all reptiles have tails. Perhaps Kipling realized that no single answer would suffice because the tails of reptiles are used for various reasons.

Some lizards use their tails in defense. The tails break off when caught by a predator, allowing the rest of the lizard to escape. I once saw a king snake stalking a brown skink, a small lizard that lives among ground vegetation in the Southeast. When the snake finally got close enough to strike at the lizard, the lizard scurried away beneath the ground litter. Yet the snake had a mouthful of lizard--the wiggling tail. By the time the snake finished its snack, the lizard was long gone. The venomous Gila monsters of the Southwest are also lizards, but their enormously fat tails are not detachable. The Gila monster uses the tail to store energy during periods when food is scarce. An African chameleon uses its tail as if it were a fifth foot, to hold onto limbs when climbing.

Some snakes also have tails that enable them to hold onto branches or vines to assist them in climbing trees. A rattlesnake uses its tail as a warning device when it feels threatened. Many harmless snakes also vibrate their tails, and if they happen to be lying in dried leaves, they too make a rattling sound. Baby copperheads and cottonmouths use their tails in an intriguing way. When they are born, and for a few months afterward, they have bright yellow tips on the ends. When the snake is coiled, the tail points up from the center and serves as a lure for prey. Small lizards and frogs apparently think the tail looks like a worm ready to be eaten.

In many dark-colored snakes, such as mud snakes and ringneck snakes, the underside of the tail is brightly colored; when threatened, the snake displays the tail, which is in conspicuous contrast to the rest of the body. The sudden display of color can startle a prospective predator. As the dark-bodied snake begins to crawl away, it lowers its tail, and some predators may then be searching for a bright color instead of one camouflaged against the dirt or mud, allowing the snake to escape. Rubber boas of California have short, blunt tails that look almost identical to the head. When threatened by a predator, this snake arranges its body in such a manner that the tail is exposed while the head is hidden safely beneath the snake. The predator that bites the-tail-that-looks-like-a-head is in for an unpleasant surprise. The boa squirts a foul-smelling liquid from the tail region that would make any predator lose its appetite.

Alligators and crocodiles use their flat-ended tails to propel themselves through water. Some sea snakes that spend almost their entire life in the water also have flattened tails that aid in swimming. Some crocodilians use their tails to knock prey off the bank and into the water.

As a rule, turtles do not use their tails for any of the purposes mentioned for other reptiles. Nonetheless, having a short, blunt tail, rather than no tail at all can be vital for a turtle. Adult male turtles, which generally have longer, stouter tails than females, use their tails to hold onto the female's tail during the mating process.

Identifying uses of reptile tails provides insight into some of the ecological purposes to which an appendage can be put. And the second grade is not too early to want to know why the creatures of the world are the way they are. Ecology is often a matter of simple questions and complex answers. Not as whimsical as Kipling's explanations, but every bit as fascinating.

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