Ephemera (Gr. that which lasts a day), the name given by Linnaeus to a genus of insects of the order neuroptera, so named from their appearing in the winged state only for a day, though in the larva and nymph states they are said to live beneath the surface of the water for two or three years. Appearing above this, in the air, generally toward evening in fine summer weather, they provide for the continuation of their race and die. The body is long, slender, and soft, the wings of very unequal size, and the abdomen with long articulated appendages. They are usually called May flies. Though but frail and delicate insects, they have been found in certain districts in France covering the ground in such enormous numbers as to be collected by cart loads for manure. One species, the ephemera albi pennis, or white-winged, is sometimes seen in such quantities by the banks of rivers as to whiten the air and the ground like drifting snow.