Adults: The upright wings and long, fine tails are unmistakable descriptors coupled with a slow, graceful flight. Identifying the adults to species is a difficult task reserved for expert entomologists.

Larvae: While quite variable in appearance, general descriptors are as follows: often three tails, gills are tiny flaps on abdominal segments, single claw on each leg. Larval gill structures are varied in shape, size, and arrangement. Species capable of living in stagnant water move their gills to regulate oxygen intake. Fast water species use their gills for adhesion to hard, smooth surfaces.

Habitat: Adults can be seen flying low over the water or on vegetation in the vicinity of their hatch site. They are attracted to lights at night. While all mayfly larvae are aquatic, habitat preference within aquatic systems varies. See the “ecology” section for more information.

Ecology: Fourteen families with 622 species in the United States make up the ephemeroptera clan. A high abundance of mayfly nymphs (larvae) in a body of water is an indication of high water quality. These delicate creatures depend on high levels of dissolved oxygen as they work to break down particulate organic matter. Larvae specializations are as unique to where they live as they are to what they eat. Most mayfly larvae are categorized as “grazers” or “collector gatherers” in their foraging habits. Algae and particulate organic matter (detritus) are their primary foods. There are many shapes and sizes of mayfly larvae and each design is specialized for a specific niche. Nymphs that live in fast moving currents have a flattened body with sprawling legs used to anchor it to rocks. Burrowing mayflies have tusks for digging and feathery, moveable, gills that obtain oxygen even in a burrow. Nymphs that swim are streamlined with short tails. Mayflies are short-lived (ephemeral) as adults and spend most of their adult lives mating and depositing eggs in or over water. Adults provide a food source for birds, bats, and fish. Adult mayflies do not feed but are a well known pest of car windshields.

Life History: Depending on the species, mayflies live as short as 90 minutes to a maximum of 72 hours. The incomplete metamorphosis cycle includes a sub-imago or “dun” adult stage. This sub-imago then molts into a sexually mature imago form. The imago or “spinner” is recognized by clear wings and long, stiff tails (2-3 times body length). When ready to mate, males fly in a swarm over a body of water. The egg-carrying females enter the swarm, become fertilized, and deposit the fertile eggs over the water. The method and location of egg release is dependant upon the species. The larvae hatch from eggs as tiny versions of mature larvae. Each nymph will molt 12 to 45 times before reaching maximum size. Most species have one flight period each year where the sub-imago adult emerges from within the nymph exoskeleton.