metamorphosis

Metamorphosis is a biological process in which an animal physically changes form after birth or hatching, often resulting in a larval stage that looks very different from the adult. The transformation can involve major remodeling of tissues and organs and may occur gradually or relatively abruptly.

Metamorphoses are classified by the extent of change. Complete metamorphosis (holometabolism) includes egg, larva, pupa, and adult, a pattern seen in many insects such as butterflies, moths, beetles, bees, and flies. Incomplete metamorphosis (hemimetabolism) has egg, nymph, and adult, with nymphs resembling small adults, as in grasshoppers, true bugs, and crickets. Some groups show direct development, where young resemble adults and simply grow.

Endocrine control drives metamorphosis. In insects, ecdysone triggers molts while juvenile hormone influences developmental direction. Holometabolous development involves larval tissues often being replaced during pupation by adult structures from imaginal discs. In amphibians, thyroid hormone initiates metamorphosis from aquatic tadpoles to terrestrial or adult forms.

Evolutionary, holometabolism is considered highly successful because larvae and adults exploit different resources, reducing intraspecific competition. Metamorphosis is widespread across insects, amphibians, and some marine invertebrates, reflecting convergent strategies to occupy varied ecological niches.

In literature and culture, metamorphosis is also used metaphorically to describe dramatic transformations, most famously in Franz Kafka's The Metamorphosis.