A Mayfly (Order Ephemeroptera) landed on the back of my hand. This is a "sub-imago": essentially an adult capable of flight, it will molt once more to become sexually mature. The true adult's wings will be transparent. Mayflies are the most ancient order of flying insects with ancestors dating to the Carboniferous (300+ million years ago). Their nymphs live in water and breathe through gills. The adults do not feed and live only hours to days at most - thus the Latin translation "brief-wings" for Ephemeroptera.