Larva, a young animal that must undergo metamorphosis (a marked change in form) before it becomes an adult. The term is applied to crabs, barnacles, frogs, and many other animals in stages of development in which they bear little or no resemblance to the adults, but chiefly it is applied to insects that pass through the successive stages of egg, larva, pupa, and adult. Such insects—including moths and butterflies, beetles, and flies—are said to undergo complete metamorphosis.

The immature forms of insects that undergo incomplete metamorphosis (do not pass through a pupal stage) are called nymphs, or naiads. Grasshoppers, dragonflies, and many other insects, including all true bugs, undergo incomplete metamorphosis. The young of primitive insects, such as silverfish, which develop only in size and sexual maturity, are simply called young.