Mayflies

Definition

Aquatic insects of the order Ephemeroptera, characterized by an ancient wing venation pattern held vertically at rest, a brief adult lifespan (often hours to days), and an extended aquatic nymphal stage. Adults typically have non-functional mouthparts and do not feed; reproduction occurs in swarming mating flights. The order comprises over 3,000 species in 42 families and, together with dragonflies and damselflies, forms the Palaeoptera—one of the most basal lineages of winged insects.

Etymology

From 'May' (referring to their typical emergence season in temperate regions) + 'fly', though adults appear across spring and summer months depending on latitude and species.

Example

The burrowing mayfly Hexagenia limbata emerges synchronously from Great Lakes sediments in billions, creating visible radar signatures and providing critical food pulses for fish, birds, and terrestrial insectivores.

Synonyms

• Ephemeroptera (order name)
• Dayflies (archaic)
• Shadflies (regional)

Related Terms

• Ephemeroptera
• Palaeoptera
• Aquatic Insects
• Incomplete metamorphosis
• Swarming
• Subimago
• Drake (angling term)
• Bioindicator

Usage Notes

The common name emphasizes the fleeting adult stage, though nymphs live months to years underwater. 'Mayfly' is sometimes used loosely in angling for any Ephemeroptera, but specialists distinguish families by body form and habitat preference. The subimago (dun) stage—unique among insects where a winged molt occurs—is critical for identification and fly-fishing mimicry. Not to be confused with caddisflies (Trichoptera) or stoneflies (Plecoptera), which share aquatic habitats but differ in wing posture, antennae length, and life history.