Mayfly, a soft-bodied insect with transparent wings and two or three tail-like projections. Adult mayflies gather in swarms in early spring, often under street lights. Mayflies are eaten by birds, bats, frogs, and fish, particularly trout. Several fishing lures are modeled after mayflies.

The mayflyThe mayfly is a dainty insect with lacy wings and a slender, forked tail.

There are about 1,500 species of mayflies, 500 of which are found in North America. The adult mayfly is about one inch (2.5 cm) long. The best-known North American species is the common mayfly.

The female mayfly deposits her eggs on the surface of a stream or pond, or attaches them to submerged rocks. The young, called water nymphs (or naiads), feed on algae and breathe through pairs of tracheal gills on their abdomen. The nymph stage lasts two weeks to two years, depending on the species. The water nymph emerges in spring, commonly in May (hence the insect's name). The nymph sheds its skin twice before becoming an adult. After the first molt, the nymph becomes a subadult, or subimago. It has wings but lacks reproductive organs. It then sheds its skin again and becomes an adult, or imago. The mayfly is unique among insects in that it molts in winged form. The adult mayfly lacks mouthparts and is unable to eat. It lives no more than two days, during which time it finds a mate and breeds.

Mayflies make up the order Ephemeroptera. The common mayfly is Hexagenia bilineata. Mayflies are not related to true flies (order Diptera).