Types of Insect Metamorphosis

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What is 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.
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.

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.

Insects may undergo gradual metamorphosis, where transformation is subtle, or complete metamorphosis, where each stage of the life cycle appears quite different from the others. In some insects, there may be no true metamorphosis at all. With regard to metamorphosis, entomologists divide insects into three groups – ametabolous, hemimetabolous, and holometabolous.

Illustration by Debbie Hadley, using drawings from Insects - Their Ways and Means of Living by Robert Evans Snodgrass, U.S. Bureau of Entomology. These drawings are in the public domain.

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Little or No Metamorphosis

The springtail is anametabolous, with no metamorphosis.
The springtail is anametabolous, with no metamorphosis.

The most primitive insects, such as springtails, undergo little or no true metamorphosis during their life cycles. Entomologists refer to these insects as ametabolous, from the Greek for "having no metamorphosis". In ametabolous insects, the immature looks like a tiny version of the adult when it emerges from the egg. It will molt and grow until it reaches sexual maturity. Ametabolous insects include silverfish, firebrats, and springtails.

Illustration by Debbie Hadley.

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Simple or Gradual Metamorphosis

The periodical cicada is hemimetabolous, an insect with gradual metamorphosis.
The periodical cicada is hemimetabolous, an insect with gradual metamorphosis.

In gradual metamorphosis, three life stages occur: 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. The nymph resembles the adult in most ways, particularly in appearance. Usually, the nymph also shares the same habitat and food as the adults, and will exhibit similar behaviors. In winged insects, the nymph develops wings externally as it molts and grows. Functional and fully-formed wings mark the adult stage.

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

Illustration by Debbie Hadley, using drawings from Insects - Their Ways and Means of Living by Robert Evans Snodgrass, U.S. Bureau of Entomology. These drawings are in the public domain.

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Complete Metamorphosis

The house fly is holometabolous, with complete metamorphosis.
The house fly is holometabolous, with complete metamorphosis.

Most insects undergo complete metamorphosis. Each stage of the life cycle – egg, larva, pupa, and adult – looks different from the others. 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 a unique name 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.

Illustration by Debbie Hadley, using drawings from Insects - Their Ways and Means of Living by Robert Evans Snodgrass, U.S. Bureau of Entomology. These drawings are in the public domain.

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Hadley, Debbie. "Types of Insect Metamorphosis." ThoughtCo, May. 16, 2014, thoughtco.com/types-of-insect-metamorphosis-1968347. Hadley, Debbie. (2014, May 16). Types of Insect Metamorphosis. Retrieved from https://www.thoughtco.com/types-of-insect-metamorphosis-1968347 Hadley, Debbie. "Types of Insect Metamorphosis." ThoughtCo. https://www.thoughtco.com/types-of-insect-metamorphosis-1968347 (accessed January 22, 2018).