Mayfly - Siphlonurus autumnalis (Siphlonurus autumnalis )

Ecology and life history

This species is associated with medium to large rivers and has been taken from rocky but somewhat quiet edgewaters along relatively large rivers in the Northwest. It has also been collected at a cold, spring brook in Montana.

All mayflies are aquatic in their developmental stages. Their lifespan is spent almost entirely undergoing numerous molts.

Larval existence is usually three to six months but can be as short as two weeks or as long as two years. The nymphs are generalists, moving over stones and weeds to graze off bacteria, collecting from sediments or feeding on detritus. Adults do not eat; they have nonfunctional digestive systems.

Unlike most insects, the mayfly typically has two winged stages. It is the only existing insect that molts after getting functional wings. The first stage, the subimago, is a subadult stage typically found perched on shoreline vegetation; it lasts from four minutes to 48 hours (correlated with the lifespan of the species’ adult stage). Soon after it is formed (in most species), the subimago molts to form the imago, the true adult or reproductive stage. Both subimagos and adults tend to remain along banks at emergence sites.

Mayfly eggs are eaten by snails and caddisfly larvae. The nymphs may be eaten by fish, frogs, birds, flies, or water beetles. The subimagos are eaten by fish, birds, dragonflies, water beetles, or other predatory insects.

Mating occurs in a swarm, and the eggs are laid as the female skims the water. The eggs sink to the bottom, and develop sticky substances or adhesive disks, depending on the species.

Adults of most species are short-lived (less than two hours to three days).

Mayfly dispersal is limited in the larval stage by drainage systems and in adult stages by relatively short life spans and weak flying ability of gravid females. Dispersal at the population level has been little studied. Adult dispersal ability has not been extensively studied; however, several characteristics appear to limit occurrences to a short distance, including weak flying ability, extremely short life cycle, and tendency to remain in the area of emergence. Once a population becomes established, there is little opportunity for exchange of genetic materials with populations in other drainage systems.

Geographic range

In Washington, this species occurred historically in Clallam, Grays Harbor, Jefferson, Lewis, and Pierce Counties; it was recently collected in Clallam County.

For a map of range-wide distribution and conservation status, check out NatureServe Explorer.