Pliability and thickness of the exoskeleton differ in each developmental stage. Bees, butterflies and moths undergo 'complete metamorphosis,' in which the egg becomes a larva that receives adequate nutrition for growth and then enters a resting stage, or pupa. A pupa's cuticle is soft, but the wax walls of a brood cell further protect it. The pupa does not move around; it does not feed, and it is extremely vulnerable to predators and parasites. Even though pupae appear quiescent, they reorganize themselves internally very rapidly. Wings form internally to appear externally just before the pupa changes to an adult.

More than ninety percent of insects display complete metamorphosis. Insects undergoing incomplete metamorphosis avoid the pupal stage. They shed their exoskeletons at intervals (ecdy-sis or molting) while moving and foraging. Growth follows each molt, as the immature form, called an instar, grows stepwise to adulthood. Instars may molt four to eight times, and in some species, molting occurs thirty times. Each time an instar molts, its body is usually pale and soft, but the body soon swells in an hour or two before the exoskeleton hardens and darkens.

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