'Hemimetabolism' or 'hemimetaboly', also called 'incomplete
metamorphosis', is a term used to describe the mode of development of certain insects that includes three distinct stages: the
egg,
nymph, and the adult stage, or
imago. These groups go through gradual changes; there is no
pupal stage. The nymph often resemble the adult somewhat, as they have compound eyes, developed legs and wing stubs visible on the outside.
Examples of hemimetabolous insects
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Hemiptera (
scale insects,
aphids,
whitefly,
cicadas,
leafhoppers and true bugs)
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Orthoptera (
grasshoppers and
crickets)
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Mantodea (
praying mantids)
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Blattaria (
cockroaches)
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Dermaptera (
earwigs)
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Odonata (
dragonflies and
damselflies).
Previously used nomenclature
Hemimetabolous insects used to be further divided into two categories: 'paurometaboly' and 'heterometaboly'. In paurometabolous insects, the
nymph and the adult would live in the same environment (water, air, soil, etc.). This is the case of the
Orthoptera (grasshoppers and crickets) and some
Hemiptera (true bugs) are examples of this. The nymph and adult of heterometabolous insects live in different environments. For example,
Odonata naiad live in the water and cicada nymph underground, whereas the adults are aerial.
Terminology of aquatic entomology
In aquatic
entomology, different terminology is used when categorizing insects with incomplete
metamorphosis. Paurometabolism refers to insects whose
nymphs occupy the same environment as the adults, as in the family
Gerridae of
hemiptera. The hemimetabolous insects are those whose nymphs, called
naiads, occupy aquatic habitats while the adults are terrestrial. This includes all members of the orders
Plecoptera,
Ephemeroptera, and
Odonata. Aquatic entomologists use this categorization because it specifies whether the adult will occupy an aquatic or semi aquatic habitat, or will be terrestrial. This classification system is similar to previously used nomenclature in terrestrial entomology.
See also
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Holometabolism
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Ametabolism
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Metamorphosis