RAINY WEATHER BRINGS MORE FROG QUESTIONS

by Whit Gibbons

December 13, 2009

Whether because of the exceptionally rainy weather or some other reason, I have received more questions about frogs and toads than usual. Michael Dorcas, an amphibian biologist at Davidson College, Charlotte, N.C., has also noticed an increase in questions. The following are our answers to some of those questions.

Q. Where are the most species of frogs and toads found in the United States?

A. Indisputably, the greatest biodiversity of U.S. frogs and toads is in the southeastern states from the Carolinas to Florida, Georgia, and Alabama. Each of those states has at least 30 species of native frogs, which is more than any of the western states.

Q. Why do so many frogs have long legs?

A. Frogs have comparatively longer legs, particularly the hind legs, than any other group of vertebrate animals. Some species of frogs have much longer legs than others, but the hind limbs are longer than the front limbs in all species of frogs. Toads generally have shorter legs in proportion to their body than the true frogs or the treefrogs, but even toads have hind legs that are relatively longer than their front legs or than the hind legs of most other animal species. The most obvious reason for having strong, elongated hind legs is that they allow the animal to jump long distances relative to its body length. Jumping, which aids in rapid transportation, is especially effective for escaping from predators, thus offering a significant advantage to an otherwise vulnerable prey species. The single adaptation of jumping, or saltatory (proceeding by leaps) locomotion, is considered by many amphibian biologists to be responsible for the worldwide success, that is, high biodiversity, of this group of amphibians. The powerful hind legs of some frogs are used not only for jumping but also for swimming. A large bullfrog can jump several times its body length from a riverbank into the water, and its strong legs and large webbed feet can then be used to propel the frog rapidly underwater. The long legs of treefrogs are used for reaching out to grasp the next leaf or tree branch.

Q. How far can frogs jump?

A. Many frogs can jump at least 30 times the length of their body, and some of the smaller species of treefrogs can probably jump more than 50 times their own length. This would be equivalent to a human jumping the length of a football field without a running start (as if a running start would really matter that much). Although the exact record is disputed, a couple of larger species within the family Ranidae, which includes the bullfrogs and leopard frogs, have been reported to jump more than 30 feet from a sitting position. Some of the frogs in the genus Rhacophorus, the so-called flying or gliding frogs in Asia, can go the longest distances, depending on the height they jump from, because they actually glide through the air. Because jumping long distances is important to the survival of many species of frogs for predator avoidance, the skeleton of some species is modified to absorb shock when they land, although the force of landing for small frogs is of little consequence. Some frogs, such as the narrow-mouth toads of the Southeast or the Mexican burrowing frogs, can only hop a few inches at most.

Q. Are frogs slimy?

A. Most frogs have moist skin, and frogs closely associated with aquatic habitats typically have slimier skin than do those that are found on land in drier areas. Some frogs produce mucus that makes them so slimy that they are difficult to hold on to, which allows them to escape from some predators. All tadpoles are slippery. Frogs have lungs, but many species also breathe by transporting oxygen from the air across the skin. For this form of respiration to occur, the skin must remain moist. In general, toads have drier skin than do other frogs, but there are a number of exceptions to this rule. Many frogs and toads produce toxins in the skin that make them unpalatable to some predators. This toxin is mixed in as part of the "slime" on the back and legs of poisonous frogs.

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