Red-eared turtle hatching out of its egg

Egg layer

Oviparous animals lay eggs, inside which the young then develop before hatching occurs. Birds, reptiles, amphibians, fish, invertebrates and even some mammals (the monotremes) all lay eggs but they're of very different size and construction. The patterns on bird eggs are produced by glands right at the last moment as the egg is laid. For terrestrial species that lay their eggs on land, a waterproof shell prevents the contents from drying out.

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Egg size range

An illustration showing the range of egg sizes

A comparison of egg size

Animals with this behaviour





Cartilaginous fish

Ray-finned fishes





Crabs, shrimp and krill


Snails and slugs


Polychaete worms

Sea urchins


BBC News about Egg layer

Video collections

Take a trip through the natural world with our themed collections of video clips from the natural history archive.

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