Tadpole, also called polliwog, is an immature frog or toad. A tadpole is a larva, which is an early stage of an animal. Tadpoles live in water. When a tadpole hatches from its egg, it looks like a small fish. The tadpole grows larger and eventually develops the physical characteristics of the mature animal. The process of changing from a larva to an adult is called metamorphosis. The tadpole stage may last from 10 days to more than 2 years, depending on the species of frog or toad.