Life Cycles
Most insects come from fertilized eggs that are laid by the adult female. There are, however, exceptions. The eggs of some insects, for example, hatch within the female's body and the young are born alive; this is called viviparous birth. Some female insects produce young without mating, a process called parthenogenesis. And some insects are able to reproduce while immature.
The development followed by most insects is called metamorphosis. There are two types: incomplete and complete.
This type of metamorphosis takes place in three stages—egg, nymph, and adult. Nymphs hatched from the eggs look like miniature adults, except they lack wings and are sexually immature. As a nymph grows and matures, the exoskeleton is shed, or molted, several times. Insects that undergo incomplete metamorphosis include grasshoppers and dragonflies. The nymphs of dragonflies and certain other insects are aquatic and are called naiads.
Incomplete metamorphosis takes place in three stages: egg, nymph, and adult.This type of metamorphosis takes place in four stages—egg, larva, pupa, and adult. It is the most complex form of development among insects and is found in such insects as bees, flies, and butterflies.
A larva hatches from the egg. It is worm-like, and does not resemble the adult insect it will become. Examples of larvae are caterpillars, grubs, maggots, army worms, and wrigglers. Some of the greatest destruction by insects occurs when they are in the larval stage. During this period they grow rapidly and require large amounts of food. The larva molts several times.
During the pupal stage, the insect is usually enclosed in a case. The pupa appears to be inactive, but major structural changes take place during this period. At the end of the pupal stage, the fully grown, mature insect emerges.
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