In some mining and industrial sites, surveys of frogs in the local area have been used to detect accidental pollution of waterways. The life cycle of a frog Most people only realise that frogs are about when they hear them calling near a pond or stream. Each species makes its own particular sound, but it is the male frog who does all of the calling, to attract the females. If the female frog is also ready to breed, she will approach the male frog. As she releases her eggs, the male frog releases sperm over the eggs.
Fertilisation occurs outside of the female's body, usually in pond water.
The fertilised eggs develop and hatch to produce tiny tadpoles, which grow and develop into frogs over a period of months. This change from tadpole to frog is called metamorphosis. The process involves not only the loss of the tail and the growth of legs and arms, but also the replacement of the tadpole's internal gills with lungs. Its digestive system also changes, to cope with a diet of insects rather than algae and decaying animal matter. The aquatic tadpole metamorphoses to become a land-dwelling frog.