Larva

A larva is an immature stage that hatches from the egg looking, and often living, quite differently from the adult it will become. Caterpillars are the larvae of butterflies and moths, maggots those of flies, grubs those of beetles, and tadpoles those of frogs. Many marine invertebrates, from crabs and barnacles to sea urchins and corals, also start life as tiny swimming larvae that drift in the plankton.

Larva and adult often specialize in different jobs. In insects with complete metamorphosis, the larva is built for eating and growing: it feeds, molts its cuticle several times as it enlarges, and then becomes a pupa, inside which the body is rebuilt into the adult form. Because larvae and adults eat different foods and live in different places, they do not compete with each other. In many sea creatures the larva mainly serves to spread the species far from its parents before it settles and transforms. Hormones control these changes; in insects, juvenile hormone keeps a larva in the larval state, and its disappearance allows metamorphosis.

Larvae matter in practice too: forensic entomologists estimate time since death from the age of fly larvae on a body, and many crop pests do their damage as larvae.