Varies, but most species have a body ¾- to 1-inch in length.
Varies from pale white to brown to black. Some have bright streaks of yellow or another color.
Mayflies are also known as shadflies or lakeflies. With four wings, a mayfly has three long hair-like appendages extending from the abdomen that are characteristic of these insects. At rest, adult mayflies hold their two pair of large membranous wings folded vertically above their abdomens. Adults live only a short time, long enough to mate and lay eggs. They do not feed. Eggs are deposited in water and the nymphs live at the bottom of the stream, pond and lake where they feed on small aquatic plants, animals and organic material. Typically, mayflies produce but one generation per year and the adults of a particular species emerge in large numbers at the same time. At times, the emerging species become massive swarms where mayflies literally cover the ground in piles after mating. Adults become structural pests when they are attracted to lights at night, sometimes in tremendous numbers.
These insects develop in ponds, lakes and rivers. They are an important part of the aquatic ecosystem because they are an important food source for many animals, especially fish, frogs and other aquatic insects. In fact, the mayfly is an important insect to the fly fisherman who will use many variations of artificial flies to mimic mayfly larvae and adults in the quest to land trout.
Mayflies cannot be controlled through treatments because they breed in aquatic environments and only become pests when attracted by outdoor lights to buildings. Any emergence of mayflies, however, should last only a few days. Where these insects become a problem, exterior light fixtures should be turned off or you should use yellow “bug lights” bulbs. Commercial buildings should use sodium vapor lamps in fixtures rather than mercury vapor lights.