Heptagenia longicauda (Stephens 1836)

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).

This mayfly is a priority species under the UK Biodiversity Action Plan (UK BAP). Further searches for this species are proposed; the Species Action Plan aims to maintain any new populations should come to light as a result (2). The Ephemeroptera Recording Scheme has provided information on the identification of the nymphs of this important rare species on its website (3).

This mayfly is very rare in Britain, and has only ever been found three times in this country (3). The aquatic nymphs of Heptagenia longicauda can be distinguished from those of the similar species H. sulphurea by the details of the filamentous gills at the very tip of the abdomen (3). All adult mayflies, which are very short-lived, fly weakly on their gauzy, delicate wings. The wings are not folded over the body when at rest, but are held aloft; this characteristic has earned mayflies the alternative name of 'upwing flies'(4). Mayflies are so called because in many species the adults emerge in May. They are not true flies, however, but belong to the order Ephemeroptera, the most primitive group of winged insects (5).

The nymphs of Heptagenia longicauda are known to occupy riffles and shallows in lowland areas of large, clean rivers (2).

The first record of this mayfly in Britain occurred in 1868 near Reading, Berkshire along the Kennet and Holybrook Canal. It was then found at Staines, Middlesex in 1904. The species was last recorded in Britain in 1933 on the River Wey in Surrey, and despite dedicated searches, it has not been found since (2). It is thought that the species may be surviving elsewhere at present (3). In mainland Europe the species is fairly widely recorded (2).

Classified as Endangered in Great Britain (2).

The threats facing this species in Britain are unknown at present (2).