The insect whose adult stage typically lasts only about one day is the mayfly. This brief winged period is so characteristic that the order’s scientific name, Ephemeroptera, comes from Greek words meaning “lasting a day” and “wing.”
Most of a mayfly’s life is spent underwater as an aquatic nymph. Depending on the species and environmental conditions, this immature stage may last from several months to several years. Nymphs molt repeatedly while feeding on algae, plant material, or organic debris before emerging into their short adult phase.
Mayflies are unusual because they molt once more after developing functional wings. This winged immature stage is called a subimago, or “dun” by fly-fishing anglers. After another molt, the insect becomes a sexually mature imago. Adults generally focus on reproduction rather than feeding; many have reduced or nonfunctional mouthparts.
“One day” is an average shorthand, not a strict limit for every species. Some adults survive longer, while the female Dolania americana can live for less than five minutes. Adults often emerge in large synchronized swarms, helping them find mates and overwhelming predators.