There are about1500 species, but only 500 of them occur in North America. A mayfly has four transparent wings held vertically, two or three long tail filaments, short antennae and bulging eyes that are sensitive to light.
Some nymphs live in burrows in the mud, while others live in quiet or swift waters.
As the nymphs eat, they grow larger and larger so they have to shed a lot of times, because their skins become too tight. Their diet consists of small water animals and other plant fragments. Mayfly nymphs have pads on their backs where future wings will be grown. After 10 to 20 molts, mayflies transform into a flying, dull- colored winged insect, called dun or subimago. This stage may last a day or more.