may·fly / ˈmāˌflī/ • n. (pl. -flies) a short-lived, slender insect (order Ephemeroptera) with delicate, transparent wings and two or three long filaments on the tail. It lives close to water, where the chiefly herbivorous aquatic larvae develop.

mayfly Soft-bodied insect found worldwide. The adult does not eat and lives only a few days, but the aquatic larvae (nymph) may live several years. Adults have triangular front wings, characteristic thread-like tails, and vestigial mouthparts; they often emerge from streams and rivers in swarms. Length: 10–25mm (0.4–lin). Order Ephemeroptera.

mayfly this short-lived insect is proverbial for its brief existence.