Why do beetles have such hard wing covers?

The beetle forewings are transformed into elytra, tough shields that meet along a straight line down the back. These protective covers can be especially useful for insects that live in wood, leaf litter, soil or under bark, where abrasion and predators are constant threats. The flight wings fold under the elytra when not in use, keeping them safe and compact. Beetles are the largest insect order, with over 400,000 described species, so this design has clearly been successful evolutionarily.