Metamorphosis usually takes several weeks. Species that breed in temporary ponds may develop more quickly than this, for if the pond dries up too soon, the underdeveloped tadpoles will perish. By contrast, bullfrog tadpoles may take several years to grow into frogs.
The changes begin when the hind legs sprout. Soon after, lungs develop and the front legs appear. Meanwhile, the tail gradually shrinks. Just before becoming a frog, the tadpole's gills disappear. The tiny froglet emerges from the water with just a stump of a tail, which soon disappears.
In the wild, most frogs live for just a few years. In captivity, well-cared-for frogs can live for 10 or even 20 years. One toad reportedly lived for 36 years under the front steps of a house in England. This toad is said to have been so tame that often came out to be fed and have its back scratched.
gastric brooding frog of Australia swallows her fertilized eggs. The
tadpoles remain in her stomach for up to 8 weeks, until finally hopping
out of her mouth as little frogs. During the brooding period, gastric
secretions cease--otherwise she would digest her own offspring. Among
Darwin frogs, it is the male who swallows and stores the developing
tadpoles--in his vocal sac.
Midwife Toads attach the fertilized eggs to their hind legs. The male carries the eggs around this way for about a month, sometimes dipping them in water to keep them moist. When the eggs are ready to hatch, he brings them to a pond and releases them.
Barking frogs, which live
on rocky cliffs in Texas, are equally devoted fathers. (This toad-like
frog is so named because it has a voice like the yapping of a small
dog.) After the female lays her eggs in a protected crevice, the male
fertilizes and then guards them. For four or five weeks he waits by
the eggs, moistening them with his urine when they become too dry, until
finally the froglets emerge.
© 1999, The Exploratorium