Frogs’ eggs become tadpoles with in two weeks of being laid in the water, but tadpoles may take anything from two months to three years to change completely into frogs.
The time taken seems to depend on the environment. Tadpoles will generally develop faster in warmer waters. Also the more advanced species of frog have simplified and shortened the process of transformation.
Tadpoles, like fish, breathe through gills. They develop lungs during the change-over, gain legs and lose their tails. The menu changes, too-from plants to very small insects.