The Types and Stages of Insect Metamorphosis

Black Swallowtail (Papilio Polyxenes) caterpillar pupating into chrysalis, Hill Country, Texas, USA
Danita Delimont / Getty Images

What is metamorphosis? With a few odd exceptions, all insect life begins as an egg. After leaving the egg, an insect must grow and transform until reaching adulthood. Only the adult insect can mate and reproduce. The physical transformation of an insect from one stage of its life cycle to another is called metamorphosis.

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What Are the Types of Metamorphosis?

The physical transformation of insects from one life stage to the next is called metamorphosis. Insects may undergo gradual metamorphosis, complete metamorphosis, or none at all.
Illustration by Debbie Hadley

Insects may undergo gradual metamorphosis, wherein the transformation is subtle, or complete metamorphosis, wherein each stage of the life cycle appears distinct from the others. 

Yet other insects may not undergo metamorphosis at all. 

Entomologists classify insects into three groups based on the types of metamorphosis they undergo – ametabolous, hemimetabolous, and holometabolous.

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Little or No Metamorphosis

The springtail is anametabolous, with no metamorphosis.
Illustration by Debbie Hadley

The most primitive insects, such as springtails, silverfish, firebrats, undergo little or no true metamorphosis during their life cycles. Entomologists refer to these insects as ametabolous, from the Greek for "having no metamorphosis". Immature ametabolous insects look like tiny versions of their adult counterparts when they emerge from the egg, molting and growing until they reach sexual maturity. 

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Simple or Gradual Metamorphosis

The periodical cicada is hemimetabolous, an insect with gradual metamorphosis.
Illustration by Debbie Hadley

In gradual metamorphosis, three life stages take place: egg, nymph, and adult. Insects with gradual metamorphosis are said to be hemimetabolous (hemi = part). Some entomologists refer to this type of transformation as incomplete metamorphosis. 

Growth happens during the nymph stage. Nymphs resemble the adults in most ways, particularly in appearance, exhibit similar behaviors, and typically share the same habitat and food as the adults.

In winged insects, nymphs develop external wings as they molt and grow. Functional, fully-formed wings mark the adult stage.

Some hemimetabolous insects include grasshoppers, mantids, cockroaches, termites, dragonflies, and all true bugs.

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Complete Metamorphosis

The house fly is holometabolous, with complete metamorphosis.
Illustration by Debbie Hadley

Most insects undergo complete metamorphosis. Each stage of the life cycle – egg, larva, pupa, and adult – looks different from the next. Entomologists call these insects holometabolous (holo = total).

The larvae of holometabolous insects bear no resemblance to their adult parents. Their habitats and food sources may be entirely different from the adults as well. Larvae grow and molt, usually multiple times. Some insect orders have unique names for their larval forms: butterfly and moth larvae are caterpillars; fly larvae are maggots, and beetle larvae are grubs.

When the larva molts for the final time, it transforms into a pupa. The pupal stage is usually considered a resting stage, although much activity occurs internally, hidden from view. The larval tissues and organs break down entirely, then reorganize into the adult form. After the reorganization is complete, the pupa molts to reveal the mature adult with functional wings.

Most of the world's insect species are holometabolous, including butterflies and moths, true flies, ants, bees, and beetles.