Insects are the only invertebrates that evolved flight. Our understanding of their remarkable flight abilities remains incomplete.
Insect wings are outgrowths of the exoskeleton. There are commonly 2 pairs: the forewings and hindwings, though a few insects lack hindwings.
In some species, only 1 sex has wings; typically, the male. Velvet ants and twisted-wing parasites (Strepsiptera) are exemplary.
Strepsipterans 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 some eusocial species, such as ants and termites, flight is selective. Workers don’t have wings.
Wings may be produced only at a certain time in the life cycle. Aphids wing it only during a dispersal phase.
Insects wings are cuticles made from chitin: the 2nd-most common natural material due to its toughness. Grasshopper legs are also chitin cuticles. For their weight, grasshopper legs are one of the sturdiest organic constructions known.
The cuticle membranes of insect wings are not so tough. They are instead subject to cracking. Yet grasshoppers and locust fly for days, over deserts and oceans, on wings 10 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. Veins that act as crack barriers increase wing durability by 50%.
Wing veins are heavier than the cuticle membrane. There is a mathematically ideal ratio between the protection that veins provide versus the additional weight they impose. Insect wings possess the optimal trade-off between lightweight cuticle membrane segments and vein patterning. Insect wings are a miraculously ideal adaptation.
Insect wings start as living tissue. During maturation into adulthood the cells between the strut work of wing veins die. The dried-out zones may become cellophane-clear or take on coloration; bordered by the vein network, wings may look like stained glass in a cathedral window. How that happens has been mysterious until quite recently.
It was long thought adult insect wings were themselves simply structural cells; as alive as toenails. But they are instead living, breathing appendages. Wing veins have their own respiratory tubes, nerves, and such.