What is a primary characteristic differentiating complete from incomplete metamorphosis?

The primary characteristic that differentiates complete metamorphosis from incomplete metamorphosis is the presence of a pupal stage. In organisms that undergo complete metamorphosis, such as butterflies, beetles, and bees, the life cycle includes four distinct stages: egg, larva, pupa, and adult. The pupal stage is a transformative phase during which the organism undergoes significant changes, often within a protective casing, allowing it to emerge in a completely different form as an adult.

In contrast, incomplete metamorphosis includes three stages: egg, nymph, and adult. The nymphs often resemble smaller versions of the adult and do not have a pupal stage. As they mature, nymphs go through a series of molts before becoming adults, but they do not undergo the dramatic transformation associated with the pupal stage.

Understanding this key difference helps clarify the life cycles of different insect groups and the varying developmental processes they undergo as they progress from immature forms to fully developed adults.