How are insect wings built from the exoskeleton?

Insect wings are formed as paired outgrowths or folds of the integument, which is the outer body covering of the arthropod exoskeleton. Specifically, these structures bud out from the wall of the thorax.

During development, these cuticular sacs flatten, pressing two layers of membrane together. This structure is then stiffened by thickenings of the cuticle that form cylindrical veins. These veins serve a vital function by carrying tracheae, nerves, and circulating blood to all parts of the wing. While the wings of most insects are thin and membranous, in some groups—such as beetles—the forewings have become thick and horny, serving as protective sheaths for the delicate hindwings.12