Instar
An
instar is a developmental stage of arthropods, such as insects, between each moult, until sexual maturity is reached. Arthropods must shed the exoskeleton in order to grow or assume a new form. Differences between instars can often be seen in altered body proportions, colors, patterns, or changes in the number of body segments. After moulting, i.e. shedding their exoskeleton, the juvenile arthropods continue in their life cycle until they either pupate or moult again. This period of growth, instar, is fixed. Some arthropods can continue to moult after sexual maturity, but these subsequent moults are generally not called instars. For most insect species, the term
instar is used to denote the developmental stage of the larval or nymphal forms of holometabolous or hemimetabolous insects, but the term can be used to describe any developmental stage including pupa or imago. Two instars of a caterpillar of
Papilio polytes The number of instars an insect undergoes depends on the species and the environmental conditions. Lower temperatures and humidity often slow the rate of development.