Frogs are usually small animals that have smooth, moist skin, bulging eyes, and external eardrums behind the eyes; the adults lack a tail. Frogs have long hind legs, and most species can take long leaps. Many species also have webbed feet, making them excellent swimmers. Most frogs, especially males, are quite vocal. As the frog forces air through the voice box, or larynx, the vocal cords vibrate to make calls distinctive of its species.
A much louder sound is produced by the males of species that possess vocal sacs, which swell enormously when the frog calls to attract a mate. The frog’s tongue is attached at the front of the mouth instead of at the rear, and it is covered with a sticky substance, making it an efficient trap. Like most amphibians, most frogs pass through a free-living fishlike larval stage before undergoing true metamorphosis into adult frogs.
Many of these frogs lay their eggs in water, although some lay their eggs on vegetation above the water, in wet places on land, or even on the back of one of the parents. The breeding season varies according to species and geographic region but often coincides with heavy spring or summer rains. Tadpoles have gills and a tail, and most feed on algae and other vegetation, although a few are carnivorous and may even feed on their siblings. As tadpoles mature, the tail is absorbed, lungs develop, the gills disappear, legs appear, and the adult frog form is established.
Some frogs, especially in the tropics, do not go through a larval phase; these frogs lay eggs, usually in damp places out of water, that hatch directly into froglets. Behavior Frogs live in a variety of habitats, but most prefer moist regions. Although they are air breathers, frogs can stay underwater for long periods, and they can breathe through the skin. Tree frogs are adapted for tree living; other frogs are permanently aquatic; still others spend most of their lives in underground burrows, coming up only to feed or breed.
Like all amphibians, a frog’s body temperature depends on its surroundings, and in colder regions frogs burrow in mud to hibernate. Some kinds, such as certain Australian frogs, estivate-that is, lie in a state of torpor during intense heat-after burying themselves in sand and clay. Frogs subsist principally on insects, worms, spiders, and centipedes. Aquatic frogs sometimes eat other frogs, tadpoles, and small fish. Larger frogs eat objects as large as mice or small snakes.
