Adult

Definition

The sexually mature, reproductively competent life stage of an organism; in arthropods, the final instar or post-metamorphic stage characterized by fully developed wings (when present), functional gonads, and cessation of somatic growth. Contrasts with immature stages (egg, larva, nymph, pupa) in which reproduction is impossible. In holometabolous insects, the adult emerges from the pupa; in hemimetabolous insects and arachnids, the adult typically follows a terminal molt after which ecdysis ceases.

Etymology

Latin adultus, past participle of adolescere, to grow up

Example

In the monarch butterfly (Danaus plexippus), the adult stage lasts 2–6 weeks for summer generations, during which individuals mate, migrate, and oviposit; only the migratory generation enters reproductive diapause and lives several months.

Synonyms

• Imago
• sexually mature stage

Related Terms

• instar
• Imago
• sexual maturity
• holometabolous
• hemimetabolous
• terminal molt
• oviposition
• Diapause
• life stage
• subadult

Usage Notes

In entomology, "adult" and "imago" are often interchangeable, though imago strictly denotes the winged adult of insects. "Adult" is preferred over "imago" for apterous groups (fleas, lice, some beetles) and arachnids. Some specialists distinguish "subadult" or "teneral adult" for individuals that have completed the terminal molt but not yet achieved full sclerotization or reproductive readiness. In population ecology, "adult" may be operationally defined by size or age thresholds when direct assessment of gonadal maturity is impractical.