Mayflies are the most primitive winged insects. The aquatic nymphs live for 2-3 years, but the adults, who do not feed, have a very brief life-span, in some species surviving for just 24 hours (5). This trait earns the mayflies the collective name ‘Ephemeroptera’, derived from the Greek ‘ephemeros’, meaning ‘lasting a day’ (4).
Mayflies are unique in that they undergo a final moult after the wings have formed. The ‘subimago’ winged insect that emerges from the nymph (known as a ‘dun’ to anglers, as they are often drab in colouration) undergoes this last moult. The mayfly that emerges, the ‘imago’ stage, is mature and will occupy its brief life with mating and, if it is a female, egg laying (4).
Very little is currently known of the ecology of this particular species of mayfly in Britain, as it is extremely rare. The nymphs feed on organic detritus and gather their food by scraping it together. The subimagos emerge at late afternoon, and imagos fly at dusk in May and June (2).