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 (antenna-like appendages extending from the tip of the abdomen).
Larval mayflies, called naiads or nymphs, are aquatic and somewhat resemble the 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 and often have a flattened head that helps them to adhere to rocks in fast-flowing water. Nymphs possess 3 (sometimes 2) long cerci extending from the tip of the abdomen.
Key identifiers of adult mayflies:
- Slender, soft-bodied
- Wings 4, membranous, extensively veined, held upright and together (like a butterfly)
- Forewings much longer than hindwings, often overlapping them
- Two long, threadlike cerci (antenna-like appendages extending from the tip of the abdomen)
- Front pair of legs are often held outward when perched
- Antennae short
- Eyes large, compound
Length: to 1¼ inches.
Statewide.
Habitat and Conservation
Usually found near water, but since they can fly, they may be found in many places.
The nymphs (or naiads) are usually found clinging to rocks in fast-flowing streams with well-oxygenated water.
Food
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.
Status
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).
Life Cycle
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 creep around on submerged 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 (called a subimago or dun). Often within hours, another molt occurs and the final stage emerges — the reproductive adults, which live for only days or hours. The adults’ only function is to reproduce.
Human Connections
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, as often occurs in the Great Lakes region, they can be a nuisance and cause problems for motorists. The swarms can be so large that meteorologists see them on Doppler radar images.
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.
Ecosystem Connections
Adult mayflies are eaten by terrestrial predators such as spiders and birds. When adult mayflies occur in swarms, it can provoke feeding frenzies among fish, which overwhelms their predators' capacity to eat them all. It is similar to the swarms of periodical cicadas.
Mayfly naiads play important roles in aquatic ecosystems, eating algae and other small items and being eaten by larger animals. 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.
