Mayfly larvae (also called naiads or nymphs) are slender and soft-bodied, like adults, though they lack wings, have a series of leaflike or feathery external gills attached along the sides or on the top rear portion of the abdomen, have smaller eyes than adults, and often have a flattened head that helps them to adhere to rocks in fast-flowing water. Nymphs possess 3 (sometimes 2) cerci (antenna-like appendages extending from the tip of the abdomen).
Adult mayflies are slender, soft-bodied, with four membranous, extensively veined wings held upright and together (like a butterfly). The forewings are much longer and often overlap the hindwings. When perching, the front pair of legs are often held outward. They have short antennae and large compound eyes. There are 2 long, threadlike cerci.
Length: ½ to 1 inch (does not include cerci or other appendages).
Habitat and Conservation
Mayfly naiads play important roles in aquatic ecosystems, eating algae and other small items and being eaten by larger animals. Often they are found clinging to rocks in fast-flowing streams with well-oxygenated water. The name of the order, Ephemeroptera, is from Greek words for “short-lived” (as in “ephemeral”) and “wing” (the “-ptera” part): As winged adults, mayflies only live a few days. The adults’ only function is to reproduce. Their swarms often provoke feeding frenzies among fish.
Different species of mayflies eat different things in their aquatic immature stages, but most creep around on rocks in lakes, ponds, streams, or at river edges, eating algae and other small plants. Once they float up to the surface and molt into a winged adult, they have only vestigial (remnant) mouthparts and cannot eat or drink.
Members of this order of insects are common throughout the state near ponds and streams. Three species of mayflies are listed as Missouri Species of Conservation Concern and thus are vulnerable to extirpation from our state: One is these is Baetisca obesa, which has no common name; the other two are Frison's serratellan mayfly (Serratella frisoni) and a heptageniid mayfly (Stenonema bednariki).
Mayflies are the only insect to have two “adult” molts. They begin life as eggs laid on the surface of the water that sink to the bottom. The aquatic nymphs of mayflies (naiads) and creep around rocks and vegetation. After months or years of growth (depending on the species), they float to the surface and molt to a winged but sexually immature subadult. Often within hours, another molt occurs and the final stage emerges — the reproductive adults which live for only days or hours.
In places where mayflies synchronize their maturation and mating cycles, appearing in swarms, they usually cause fish to swarm, too, and anglers create fishing flies to resemble adult mayflies. Where swarms are especially large, they can be a nuisance and cause problems for motorists.
All life stages of mayflies are favorite foods for fish such as trout, bass, and many others, as well as smaller aquatic predators in the food chain. Adult mayflies are also eaten by terrestrial predators such as spiders and birds.