Beetles have the largest number of described species of any group of animals. Part of their success depends on the hard forewings (elytra) that protect the hind wings and allow beetles to invade areas that would destroy exposed membranous wings of other types of insects. Elytra would not have been likely to evolve were it not for complete metamorphosis.
The wings of insect with incomplete metamorphosis (such as grasshoppers) develop externally as wing pads. The wing pads constrict the developing wing. When these insects first emerge as adults, the wing is shriveled and must be expanded. In contrast, wing formation in beetles occurs inside the pupa case. The developing wings are not constricted by wing pads. This allows the adult beetles to emerge from their pupa case with elytra that are thick. Complete metamorphosis and internal wing development allows for much greater flexibility of wing shape and character.