Mayflies: Order Ephemeroptera

Mayflies, or Ephemeroptera, are aquatic insects found in and around freshwater habitats. They are probably best known to fly-fishing enthusiasts, who tie flies to resemble both the flying adult and aquatic nymphal life stages. Ecologically, they are an important dietary component of fishes in these streams, and their presence or absence in water bodies is used as a water quality indicator.

A mayfly nymph
Photographers / Source: John Gooderham & Edward Tsyrlin

The immature or nymphal stages of mayflies are fully aquatic and are common in rivers, streams and lakes. The nymphs are elongated, with gills along the side of the abdomen and three filaments or tails arising from the tip of the abdomen. The adults are very short-lived (a few hours to a few days) and do not feed; they are merely a reproductive phase. The nymphs live for a few months – sometimes up to a year – before they emerge as adults, making the nymph the longest-lived stage.

Some nymphs are flattened and have plate-like gills on the abdomen. These usually live on the surface of rocks and are most abundant in upland streams. They feed by scraping algae from the surface of the submerged rocks. Other nymphs are common in the still waters of ponds or stream banks, and have much more delicate gills characterised by long filaments. They are often found among aquatic plants or in the crevices of submerged logs. They eat leaf and wood material as well as other organic detritus (rotting organic matter). Finally, some nymphs are robust, with a cylindrical body and spiny rigid gills that anchor individuals beneath rocks. These are usually found in stony upland streams where there is good flow. Their mouths are modified for filter-feeding on fine particulate organic material and algae; hairs on the legs assist in this process.

After hatching from the nymphs, the adults often swarm over water bodies. This enables males and females to encounter one another and mate. The ripe female then sheds her eggs into the water and the life cycle begins again.

An adult  mayfly
Photographer: Dr Ken Walker / Source: Museum Victoria