Insects are the only invertebrates that evolved flight. Human understanding of their remarkable flight abilities remains incomplete.
Insect wings are outgrowths of the exoskeleton, located on the thorax (midsection). There are commonly two pairs: the forewings and hindwings, though a few insects lack hindwings.
In some species, only one sex has wings, typically the male. Velvet ants and Strepsiptera are exemplary.
Strepsiptera are endoparasites of other insects, including bees, wasps, leafhoppers, cockroaches and silverfish. Virgin females stay within the host upon hatching, drawing flying males to them by a pheromone locator.
In eusocial species, such as ants and termites, flight is selective. Workers don’t have wings.
Wings may be produced only at a particular time in the life cycle. Aphids wing it only during a dispersal phase.
Insects wings are made from cuticle, the second most common natural material, due to its toughness. For their weight, grasshopper legs are one of the sturdiest organic constructions known.
The cuticle membranes of insects wings are not so tough. Instead, they are subject to cracking. Yet grasshoppers and locust fly for days, over deserts and oceans, on wings ten times thinner than a human hair. The wings withstand hundreds of thousands of beats.
The wings do crack at spots, but the cracks are contained by veins that crisscross each wing, segmenting a wing into hundreds of pieces. The veins that act as crack barriers increase wing durability by 50%.
Veins are heavier than the cuticle membrane. Thus there is a mathematically ideal ratio between the protection that veins provide versus the additional weight they impose. Insect wings possess the optimal tradeoff between lightweight cuticle membrane segments and vein patterning.
Ishi Nobu, Spokes of the Wheel Book 2: The Web of Life (pre-publication)
Jan-Henning Dirks & David Taylor, “Veins improve fracture toughness of insect wings,” PlosOne 7(8): e43411 (August 2012).