Mayflies

Hundreds of species in North America.

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Photo of a mayfly
Adult mayflies are slender and soft-bodied, with four membranous, extensively veined wings that are held upright and together. Two long, threadlike cerci extend from the tip of the abdomen.
Jim Rathert
Family

Various families in the order Ephemeroptera (mayflies)

Description

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).

The naiads (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

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.
Size

Length: to 1¼ inches.

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Photo of adult mayfly on a leaf
Mayfly (Adult) On Leaf
Adult mayflies are usually found near water, since they last such a brief time, are aquatic in their juvenile stages, and must lay eggs in water.

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image of a Mayfly
Mayfly (Adult) Perched Under Leaf
Once they become winged adults, mayflies only live a few days. The adults’ only function is to reproduce.

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Photo of a mayfly naiad crawling on rock underwater
Mayfly Naiad Crawling on Rock Underwater
Mayfly naiads (nymphs) often have flattened heads that help them to adhere to rocks in fast-flowing water. There are 3 (sometimes 2) long cerci extending from the abdomen tip.

mayfly_naiad_11-08-12.jpg

Photo of mayfly nymph
Mayfly Naiad
The naiads (nymphs) of mayflies somewhat resemble the adults, though they lack wings and have a series of leaflike gills attached below the abdomen.

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Pseudiron Mayfly
Pseudiron Mayfly
This mayfly nymph is probably the species Pseudiron centralis. They're sometimes called "crabwalker mayflies."

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Photo of a flatheaded mayfly nymph clinging to rock lifted out of water.
Flatheaded Mayfly Nymph
This nymph is in the family Heptageniidae, the flatheaded mayflies. It's hard to see the gills on its abdomen, since it was pulled out of the water and they are collapsed against the abdomen. But you can see the 3 cerci filaments at its hind end.
Habitat and conservation

Usually found near water. The name of the order, Ephemeroptera, is from Greek words for “short-lived” (as in “ephemeral”) and “wing” (the “-ptera” part). It’s a good name, because as winged adults, mayflies only live a few days. The adults’ only function is to reproduce. Their swarms often provoke feeding frenzies among fish. The nymphs (or naiads) play important roles in aquatic ecosystems, eating algae and other small items and being eaten by larger animals.

Foods

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.

image of Mayflies Distribution Map
Distribution in Missouri

Statewide.

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 (or flatheaded) mayfly (Maccaffertium bednariki).

Life cycle

Mayflies are the only insects 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) 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.

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, they can be a nuisance and cause problems for motorists.

Ecosystem connections

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.