Instar is the name given to the developmental stage of an arthropod between moults.

For example, after hatching from the egg and insect is said to be in its first instar. When the insect moults it is then a second instar and so on.

Instar can be used for insects undergoing complete and incomplete metamorphosis. For example, a butterfly caterpillar can go through several instars before pupation.

A photograph of a first instar assassin bug (_Triatoma infestans_).

A photograph of a first instar assassin bug Triatoma infestans.
Photograph by Centers for Disease Control and Prevention, United States Federal Government.

Other names for (or types of) Instar include:

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