hemimetaboly

Hemimetaboly, or incomplete metamorphosis, is a form of insect development in which the immature stages, called nymphs or naiads, resemble the adults in body plan but are smaller and sexually immature. The life cycle proceeds through a series of molts, with each successive instar becoming more like the adult. There is no pupal stage.

Nymphs typically lack fully developed wings; wing pads may appear in the later instars. Many hemimetabolous juveniles are aquatic (naiads) in their early instars and undergo aquatic to terrestrial transitions before reaching the winged or wingless adults, while others remain terrestrial throughout life.

Major hemimetabolous orders include Hemiptera (true bugs such as aphids, cicadas, and leafhoppers), Odonata (dragonflies and damselflies), Orthoptera (grasshoppers and crickets), Mantodea (mantises), Blattodea (cockroaches), Dermaptera (earwigs), and Plecoptera (stoneflies). In grasshoppers, nymphs resemble adults but are wingless or have small wing pads; in dragonflies, the aquatic naiads have gills and differ markedly from the winged adults.

Hemimetaboly contrasts with holometaboly, in which larvae such as caterpillars and maggot-like forms are morphologically distinct from adults and are separated by a pupal stage. It also differs from ametaboly, where juveniles resemble adults with little or no metamorphosis. The term derives from Greek hemi- "half" and metamorphosis.