Creatures such as crustaceans (e.g. lobsters, crayfish, sowbugs), millipedes, centipedes, spiders, scorpions, mites and insects are all arthropods.
Most species of arthropods lay eggs. Arthropods have external skeletons made out of non-living tissue. Much of this tissue is thickened and cannot be expanded much. In order to grow, juvenile arthropods must shed this skin, a process called molting. The new skin takes time to harden and color up.
The adults and juveniles look similar. In this case, adults may continue to molt. This strategy includes all non-insects as well as some orders of Hexapods (the class which includes insects).
Typical examples include the Odonata (damselflies and dragonflies) and the Orthoptera (grasshoppers) as well as the Hemiptera (true bugs).
The adults and juveniles may or may not look similar (depends on the order - young grasshoppers look much the same as the adults, but young dragonflies do not). Juveniles which will become winged adults develop structures known as wing buds, in which the wings will develop. (Not all juveniles of some species become winged adults, for instance many mature aphids lack wings). After the final molt, these insects emerge with wings that are, after a short curing period, fully functional. With one exception these adults do not molt - adults of the order Ephemeroptera (the mayflies) molt one more time.
Typical examples include the Lepidoptera (butterflies and moths), the Coleoptera (beetles), the Diptera (flies or true flies) and the Hymenoptera (bees, wasps and ants).
The adults and juveniles look quite different (consider the caterpillar and the butterfly or moth it becomes). This life cycle strategy includes the pupal stage, a stage in which the final development towards adulthood continues inside a sealed container. For butterflies, the pupa is called a chrysalis. For moths, the pupa is contained inside the cocoon. Adults do not molt. Not all juveniles develop into adults with wings (for instance in the case of ants, only reproductive ants develop wings).
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