Mayfly (Heptagenia longicauda)

Heptagenia longicauda adult, photographed in laboratory
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Mayfly fact file

Mayfly description

GenusHeptagenia (1)

This invertebrates_freshwater 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).


Mayfly biology

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 invertebrates_freshwater 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).


Mayfly range

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).

You can view distribution information for this species at the National Biodiversity Network Atlas.

Mayfly habitat

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


Mayfly status

Classified as Endangered in Great Britain (2).


Mayfly threats

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


Mayfly conservation

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).

There may be further information about this species available via the National Biodiversity Network Atlas.
The UK Biodiversity Action Plan for this species is available at UK BAP.

Find out more

For more on the Ephemeroptera Recording Scheme see:



This information is awaiting authentication by a species expert, and will be updated as soon as possible. If you are able to help please contact:


In arthropods (crustaceans, insects and arachnids) the abdomen is the hind region of the body, which is usually segmented to a degree (but not visibly in most spiders). In crustacea (e.g. crabs) some of the limbs attach to the abdomen; in insects the limbs are attached to the thorax (the part of the body nearest to the head) and not the abdomen. In vertebrates the abdomen is the part of the body that contains the internal organs (except the heart and lungs).
Stage of insect development, similar in appearance to the adult but sexually immature.


  1. National Biodiversity Network Species Dictionary (September 2003):
  2. UK BAP Grouped Action Plan for river shingle beetles (September 2003):
  3. Ephemeroptera Recording Scheme (September 2003):
  4. Buczacki, S. (2002) Fauna Britannica. Hamlyn, London.
  5. Burnie, D (Ed) (2001) Animal. Dorling Kindersley Limited, London.

Image credit

Heptagenia longicauda adult, photographed in laboratory  
Heptagenia longicauda adult, photographed in laboratory

© Karlheinz Teufert

Karlheinz Teufert


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