Metamorphosis: The changes in form that occur as an insect approaches adulthood. When the immature insects and the adults are similar in appearance, the process is called simple metamorphosis, and the juvenile insects are called nymphs. When the immature insects and the adults have different forms, the process is called complete metamorphosis, and the worm, or grub, like juvenile insects are called larvae. After the last larval instar, the insect changes into a pupa. In this stage, the insect does not feed or move around much. It may be covered by a protective cocoon. Eventually the insect molts for the last time and emerges as an adult.

Simple metamorphosis: The immature insects and the adults are similar in appearance, and differ mostly in size.

Simple Metamorphosis: Thysanura (Silverfish)

Complete metamorphosis: The immature insects and the adults have different forms, often live in different habitats, and may have very different behavior.

Complete Metamorphosis: Lepidoptera (Butterflies and Moths)

Egg: Most insects lay eggs in a location that offers some protection and food for the newly hatched juveniles. Many eggs are spherical, oval, or elongate, and some have elaborate sculptured shells.

Nymph: The immature form of insects with simple metamorphosis. (Stages between molts of the exoskeleton are called instars).

Simple Metamorphosis: Heteroptera (True Bugs)

Larva: The immature form (between egg and pupa) of insects with complete metamorphosis. (Stages between molts of the exoskeleton are called instars).

Pupa: When insects undergo complete metamorphosis, this is the form in between the last larval instar and the adult. In this stage, the insect does not usually feed or move around much. It may be covered by a protective cocoon.