ECOS Guide to the Ecology of the Northern Rockies

How do Insects Develop?

The word metamorphosis means a change in form and is an appropriate word to describe how an insect develops.  Some insects change a great deal as they grow from an immature insect into an adult.  There are 2 general types of metamorphosis – complete and simple.

Follow this link to see what type of metamorphosis insect orders go through. 

Complete Metamorphosis

Insects with complete metamorphosis (also called holometabolous insects) go through four stages:  egg, larva, pupa and adult.  These four stages are very different from one another - the animal looks and behaves different, may eat different types of food and usually lives in different places. 

Adult females usually lay eggs near the food the larvae will need to eat.  After the eggs hatch, the main job of larvae is to eat and grow. Due to its rigid exoskeleton, as a larva grows it must shed or molt the exoskeleton.  Each time the larva does this we call the different stages instars.  Different species go through different numbers of instars.

When it is time for the larva to become an adult it goes into the pupa stage, which sometimes involves forming a protective case.  On the outside it appears that pupae don’t really do anything because they aren’t eating or moving.  They are actually very active as the larva transforms into an adult.  After pupation, adults emerge to mate and lay eggs.

This is the life cycle for a fly (Urophora species):

This type of fly lays its eggs in the seedheads of knapweed where the developing larva will have access to food.  When the egg hatches the larva will develop and feed inside the seedhead. This fly larva will go through 3 instars before becoming a pupa.  After pupation, the adult will emerge from the seedhead to mate and lay eggs. 
Many different groups of insects go through complete metamorphosis including butterflies, moths, flies, beetles, ants, bees and wasps.

Simple Metamorphosis

Insects with simple metamorphosis go through 3 stages:  egg, larva (sometimes called nymphs or naiads) and adult.  The wings on these insects develop on the outside of the body.  If the adult insect has wings small wing pads can be seen on immature insects. 

There are three types of simple metamorphosis:  ametabolous, paurometabolous and hemimetabolous. 

Ametabolous (meaning “no” metamorphosis) is the type of metamorphosis that primitive insects go through.  Immature springtails, diplurans, proturans, bristletails and silverfish look like small versions of the adults but are not sexually mature. 

Paurometabolous insects (meaning “gradual” metamorphosis) include insects whose larvae and adults live in the same habitat, eat the same food and generally look alike except the adults have full wings.  Larvae have small wing pads that get larger each time the insect molts.

Some common insect groups with this type of metamorphosis include grasshoppers, crickets, true bugs and cockroaches.

Insects with hemimetabolous metamorphosis (meaning “incomplete” metamorphosis) are those whose larvae, sometimes called naiads, are aquatic and adults are terrestrial.  The larvae have small wing pads and may look very different from the adults.  Examples include dragonflies, mayflies and stoneflies.

Mayfly Larva

Mayfly Adult

ECOS Program
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