The final stage of a mayfly’s life cycle is called an “imago” or “spinner,” and clouds of these mating insects are often visible dancing in the air above a river. Spinners are usually easy to identify by their transparent wings, extra-long tails, and large eyes. The aquatic insects are born in the streambed and live as nymphs for up to a year. The nymphs then rise to the surface, where the winged dun breaks free of the nymphal shuck. The duns fly to streamside vegetation, where they usually live

As a mayfly larvae emerges out of its shell, this will be the most important—and only—day of its adult life. | National Geographic