Tadpoles come from newly hatched frog and toad eggs. New tadpoles have no arms or legs, and most cannot breathe atmospheric oxygen. They also have long tails. As they mature, the tadpoles develop extremities, lose their tails and those born unable to breathe air grow lungs and develop that ability.
The process by which tadpoles become adult amphibians is called metamorphosis. It happens gradually and involves dramatic changes to every aspect of the developing frog or toad.
Metamorphosis lasts six to 12 weeks. It begins with the growth of long, powerful hind legs. The tadpoles soon develop arms and absorb their tails into their growing bodies. Those born without lungs develop them and lose their gills, rising to the surface of their watery home as they learn to breathe air. This is a crucial and stressful period during which many drown because they are not able to leave the water and have no natural instinct to do so.
Metamorphosis also involves gastrointestinal changes. Most tadpoles are herbivorous, although some species cannibalize other tadpoles when sufficient vegetation is unavailable. During metamorphosis, the digestive tract shortens and adapts to the carnivorous diet of adult frogs and toads.The tadpole's narrow mouth also expands until it's as wide as its head.
In the period immediately following metamorphosis, young frogs and toads learn adult survival skills. Captive frogs released later in life find it difficult or impossible to adapt to the wild, and many of them die.