Mayflies (Order Ephemeroptera), despite their name, do not emerge only in May. Their Latin name, ephemeroptera, meaning "living a day" is much more accurate. Adult mayflies only live 1-2 days. Their evolutionary lifespan, however, is much longer; the first mayfly emerged 350 million years ago. Adults and nymphs are common food of many freshwater fish, and often bait used by fishermen are modeled after mayflies. The adult mayfly's mouthparts are vestigal, as the adult mayfly does not eat.
Adult mayflies are small to medium sized with soft bodies, and are brownish or yellowish in color. The antennae are quite small and bristle-like. Tarsi have 3-5 segments. The forewing is large and triangular, with many veins. The hindwing is small and rounded, but usually present. The wings are held together about the body when the animal is at rest. The abdomen has 2-3 hairlike tails that can be twice as long as the abdomen itself.
Mayflies undergo simple metamorphosis. Naiads have leaf-like gills on the abdomen and three hair-like tails. Naiads eat tiny plants and small aquatic animals; unlike adults, they have small mouthparts they can bite with. They can distinguished from stonefly naiads as they have 3, not 2 tail-like filaments, and gills on the abdomen and not throrax. Mayfly naiads can live up to four years. The last instar molts at the surface of the water or on an object close to the surface of the water. This form is called a subimago, and is not the adult form. Mayflies are unique among insects in that they molt after developing functional wings. The subimago is has smoky colored wings, and becomes an adult with clear wings after one more molt. Colloquially, the subimago and adult are called dun and spinner, respectively. The adult lives from 1-2 days, and does not eat. Males swarm together in large clouds, seizing up any female that enters the swarm. The eggs will be laid within an hour, on rocks or other objects near the water's surface, or deposited on the surface itself. Adults often emerge in groups, sometimes piling up on shorelines, in both spring and summer.
Nymphs are aquatic, and are generally found in freshwater ponds and streams. Adults are usually found in the vicinity of nymph habitats.
Number of species
There are 585 species found in North America, and 2100 worldwide.
There are suborders in this order, principally separated by wing venation and tarsel segmentation.