The Life Cycle of an Insect

Most insects begin life as eggs. The eggs hatch and the insect develops from an immature form to an adult. Because insects are covered in a hard exoskeleton that does not stretch, they must grow in discrete stages and molt each time. They emerge from their old skins to attain the next stage in their development.

Insects are the most diverse group of life on earth and there are many variations in insect life cycles. The four basic types of insect metamorphosis are ametabolous, paurometabolous, hemimetabolous, and holometabolous.

  1. Ametabolous Insects

    • Insects such as silverfish have ametabolous development, the simplest and most primitive type of insect life cycle. These insects lay eggs and the eggs hatch into nymphs. The nymphs are simply smaller versions of the adult form. With each molt, the nymph grows larger, but it does not undergo any major changes in its body plan. Ametabolous insects do not have wings.

    Paurometabolous Insects

    • In paurometabolous development, the only major difference between the nymphs and the adults is the wings. Only the adults are winged. Paurometabolous insects include praying mantises, stinkbugs and cockroaches. When a baby praying mantis hatches from the egg, it comes out looking just like a tiny version of the adult, but it will not be able to fly until it reaches the adult stage.

    Hemimetabolous Insects

    • In hemimetabolous insects such as dragonflies, damselflies and mayflies, the immatures are called naiads. Naiads live underwater, breathe with gills and do not have wings. Naiads hatch from eggs and grow bigger with each molt. At the time of their final molt, they emerge from the water, breathe air and have wings. You will typically find the adult insects flying around near water, because the water is where they grew up.

    Holometabolous Insects

    • Holometabolous development is also called "complete metamorphosis." The holometabolous insects are by far the most diverse and successful. The largest groups of insects are all holometabolous. In this type of development, the young are called larvae and appear wormlike. Complete metamorphosis involves the transition from egg to larva, to pupa and then to a winged adult. During the pupal stage, the insect does not feed or move. It may be surrounded by a protective cocoon, but on the inside, it is breaking down and rebuilding its body. When its development is complete, it will emerge from the pupa in the adult form. Caterpillars that develop into butterflies, maggots that develop into flies, and grubs that develop into beetles are all example of holometabolous insects. The larva and adult have completely different appearances, diets and activities and occupy different ecological niches.

    Parasitoids

    • Within these four broad types of insect life cycles, you can find endless variation and many highly specialized life cycles. For example, many small wasps and flies are parasitoids. This means that the adult form is free-living. They fly around and often feed on nectar and pollen. But the eggs are laid in another insect. The larvae complete their development within the host, feeding on the host's body from the inside. When they emerge as adults, the host is killed.