The life cycle of an insect begins with an egg, which then hatches into a larva.
For the juvenile insect, life is taken up with eating, growing, moulting, and
growing bigger until it is ready to become an adult.
To grow bigger, an insect needs to shed its tough outer exoskeleton, or moult.
When the insect is ready, the old exoskeleton cracks open and the insect slowly
crawls out. Free of its old ‘skin’, the insect stretches itself
out, puffs itself up and dries out its new exoskeleton.
Juvenile insects moult many times as they grow, often changing into quite
different organisms by the adult stage. A change in form is known as
metamorphosis. Depending upon the species, an insect’s life stages are
characterised by either complete or incomplete metamorphosis.
Insects that undergo complete metamorphosis are called holometabolous. They have
four life stages: egg, larva, pupa and adult. The larva looks dramatically
different to the adult insect, and must go through a pupal stage before it
develops into an adult.
Pupation occurs at the final moult. It is an apparent inactive stage during
which the larva undergoes dramatic change. When it emerges, the pupa has become
an adult. It has wings, fully functional reproductive parts and looks just like
Complete metamorphosis gives insects a significant survival advantage. The
adults and larvae, being different, do not compete for the same food sources
and have different predators.
Complete metamorphosis occurs in 85% of known insect species. That includes
all of the major successful insect groups such as beetles, wasps, bees, ants,
flies, moths and butterflies. Other insect species that undergo complete
metamorphosis include fleas, alderflies, lacewings, scorpion-flies and
Insects that undergo incomplete metamorphosis are called hemimetabolous. They
have three life stages: egg, nymph (larva) and adult.
A hemimetabolous insect begins life as a wingless nymph. In many cases it looks
like a miniature adult. With each successive moult, the insect increases in
size and looks more and more like an adult. On a flying insect, wings will
gradually appear. After the last moult the insect is fully adult, able to use
its wings and reproduce.
Insect species that undergo incomplete metamorphosis include silverfish,
mayflies, dragonflies, damselflies, stoneflies, cockroaches, termites, praying
mantids, earwigs, grasshoppers, stick-insects, web-spinners, booklice,
parasitic lice, true bugs and thrips.