Incomplete metamorphosis

Definition

A developmental mode in insects characterized by three life stages—egg, nymph, and adult—without an intervening pupal stage. Nymphs resemble miniature adults, typically differing only in size, wing development (often with external wing buds that enlarge through successive molts), and sexual immaturity. Each molt produces a larger nymph (instar) until the final molt yields the winged, reproductive adult (imago). The process is gradual and externally visible, contrasting with the concealed transformation of complete metamorphosis.

Etymology

Latin in- (not) + completus (finished); Greek meta- (after) + morphe (form)

Example

A grasshopper nymph hatches without wings, develops increasingly large external wing buds through five or six instars, and molts directly into a winged adult capable of reproduction—never entering a pupal stage.

Synonyms

• hemimetabolism
• hemimetaboly
• partial metamorphosis
• paurometabolism

Related Terms

• complete metamorphosis
• hemimetabolous
• Exopterygota
• nymph
• instar
• wing bud
• Juvenile hormone
• ametabolous

Usage Notes

Preferred in general entomology; 'hemimetabolism' is more common in technical literature. Paurometabolism specifically denotes gradual change where early instars differ little from adults (as in true bugs), whereas some sources restrict 'incomplete metamorphosis' to cases with pronounced nymph-adult similarity. Not used for ametabolous insects (silverfish, bristletails) where adults continue molting, or for holometabolous insects with pupal stages. The adjective form is 'hemimetabolous'.