(Greek, ephemeros = short-lived; pteron = wing)
This is the most primitive order of living, winged insects and, though small, it is nearly cosmopolitan. Nymphs of all species are aquatic and occur in relatively unpolluted, standing and running freshwaters. The adults (both subimagos and imagos) are short lived (a few minutes to several days) and usually do not move far from water.
Adults take no food and the alimentary canal of the male is inflated with air. Imagos of most species have a characteristic, aerial mating flight either over water or over nearby landmarks. A few species reproduce parthenogenetically.
Mayfly adults have two pairs of wings; the front pair is large and well developed, while the rear pair is much smaller. Often the forelegs are very long, which gives the insect a characteristic "elongated" appearance when resting. Adults have reduced mouthparts and do not feed. There are three, long bristles (caudal filaments) at the apex of the abdomen. The two outer bristles are called cerci; a long central filament may also be present to produce the three bristles most commonly seen. Well developed compound eyes are present together with three simple eyes (ocelli). The adult insect is remarkable for its delicacy and fragility and is readily crushed by even gentle touches.
Mating is accomplished during immense swarming clouds of the insects over water. The eggs are deposited in masses directly into the water by the females. The egg masses break apart and individual eggs disperse to the bottom mud. The hatched mayfly larva resembles a wingless adult (a nymph) and it feeds on plants, fungi or fine detritus; some species are carnivorous. Gills are present as a fringe along the length of the abdomen. Nymphs grow by moulting and may take up to three years to mature. On maturity, the nymph reaches the water surface and moults to produce a dull-coloured subimago. This is a winged stage but it is not yet fully adult. The subimago spends much of its time resting although it can fly. The final moult takes place after several hours or days and the adult insect then emerges.
Mayflies are extremely important in the ecology of freshwater streams. They form an important food source for many other organisms. As adults do not feed, their life is limited to several hours or at most, days. Fish eat the adults in vast quantities during egg laying or when the insects fall exhausted to the water surface. Mayfly adults can be collected by sweeping a butterfly net above the water's surface or through overhanging vegetation.
Palaeoptera with mouth-parts mandibulate in the nymph, but vestigial and nonfunctional in the adult; abdomen of both nymph and adult with 2 or 3 long caudal filaments (cerci and terminal filament). Nymph with abdominal gills; adult with subimaginal and imaginal winged stages.