Life cycle of a frog — free printable diagram

The stages of a frog's life cycle

A frog's life cycle is the classic example of metamorphosis — the animal changes body form completely rather than simply growing larger. The diagram is drawn as a circle because an adult frog returns to the water to spawn, starting the cycle again. The stages below are the ones normally labelled.

Stage 1

Egg — laid in water in a jelly-like mass called frogspawn

Stage 2

Tadpole — hatches with a tail and external gills

Stage 3

Tadpole with legs — back legs appear first, then front

Stage 4

Froglet — tail shrinks, lungs develop

Stage 5

Adult frog — leaves the water and can breed

Type of change

Metamorphosis

• The eggs are laid in water and must stay there — frogspawn has no shell and would dry out on land. That is why the whole early cycle is aquatic.
• A newly hatched tadpole breathes through gills like a fish. As it develops it grows lungs and begins coming to the surface for air, which is the change that eventually lets it live on land.
• The back legs appear before the front legs. Asking students which pair comes first is a quick way to check they are reading the diagram rather than guessing.
• The tail is not shed. It is gradually absorbed by the froglet's body and reused, which surprises most classes.
• Metamorphosis means the body form changes completely between stages. It is worth contrasting with an animal such as a human or a horse, whose young are simply smaller versions of the adult.
• How long the cycle takes varies with species and water temperature, so it is better described in general terms — several weeks to a few months for many common frogs — than as a fixed number.