The Insect Life Cycle

The insect life cycle results from a biological process called metamorphosis, where insects transform from an immature form to an adult form in two, three, or four distinct stages involving relatively abrupt changes to their body structure as the result of cell growth and cell differentiation.

There are four possible stages in the insect life cycle: egg, larvae, pupa, and adult.  Not all insects will go through all four stages. It depends on the type of metamorphosis their species follows.

All insects start out as eggs.  Some eggs require mating and fertilization by sperm to develop. Females of other insects like ants, bees, and wasps can produce female offspring (and in rare cases, males) without requiring fertilization through a process called parthenogenesis.  They will mate when they want to produce male offspring.

Throughout the life cycle of insects, they are required to shed their exoskeleton or outer skin through a process called molting.  They molt as they increase in size and may be required to do so many times in their life as they grow.

Types of Metamorphosis

After an insect hatches, it will follow one of three basic growth and development patterns.  The pattern that is followed is based on the insect species.

Simple Metamorphosis

The simplest insect growth and development pattern is called simple metamorphosis.  This occurs in certain primitive wingless insects like silverfish.  When the eggs of these species hatch, the resulting young insect looks almost identical to its adult counterpart, only smaller.  It consumes the same food in the same manner as its adult counterpart.  As the young insect grows and its outer skin becomes too tight, it occasionally molts, splitting its old exoskeleton and climbing out of it.  After they mature into an adult, they are capable of reproducing.  These insects look basically the same from birth until adulthood.

Incomplete Metamorphosis

The next insect growth and development pattern is called incomplete metamorphosis, where insects pass through three life stages: egg, nymph, and adult.  After hatching, the nymphs may or may not have a similar appearance as their adult parents. 

Insects like grasshoppers do look like their parents, only they have no wings.  The wings do not appear until they molt a few times.  Each time they molt, the wings get larger and more developed.  The last time they molt, the adult has fully developed wings.  These nymphs typically eat the same food and live in the same places as adult forms of the same species of insects. 

The nymphs of other aquatic insects like dragonflies appear quite different from their parents.  While the adults are winged and spend a great deal of time in flight, the nymphs live in water, a very different habitat from that of their parents, and breathe using gills.  These nymphs are often referred to as naiads.  After reaching maturity, the insect crawls out of the water and molts one final time to become a winged adult.

Complete Metamorphosis

The final insect growth and development pattern is called complete metamorphosis, in which the insect goes through four distinct life stages: egg, larva, pupa, and adult.  This occurs in most species of insects like butterflies and moths, ants, bees, wasps, and beetles. 

The larvae look very different from their parents and often live in different places and eat different foods than their parents do.  Most have chewing mouthparts while their parents have sucking mouthparts.  They are missing compound eyes and wings, and some do not even have legs.  Some larvae have special names like grubs for beetles, caterpillars for butterflies, or maggots for flies.  The larvae eat and grow, molting several times.

Once the larva stage has completed, the insect will stop eating and become a pupa. Prior to advancing into a pupa, the larva of some species creates a protective covering such as a cocoon created for a moth or a chrysalis for a butterfly.  During the pupa stage, the larval structures are reformed into adult organs.  Once this process is complete, the fully developed adult insect emerges from the pupal covering.