The most ancient extant lineage of winged insects. Unlike all other insects, Ephemeroptera have a winged sub-adult stage. The adults do not feed and live only a few minutes to a few days. Nymphs of all species live in freshwater. The nymphs of most species are general collectors-gatherers.
Some species are filterers or scrapers and there are a few predatory species.
Nymphs are the preferred form as many adults are secretive. Nymphs are generally abundant and easily collected by routine benthic sampling, but must be handled with care. Many species are restricted to shoreline areas. Some benthic forms from large rivers are rarely collected. Active swimmers may avoid nets.