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…
Source: Living With Insects Blog