Mayflies of special interest to the Ephemeroptera Recording Scheme
The purpose of this short note is to provide information on two species of mayfly that are of particular interest to the Ephemeroptera Recording Scheme. Heptagenia longicauda, is listed as a UK Biodiversity priority species, whilst if a population of Arthroplea congener was found this species would be probably merit inclusion in the Red Data Book of Insects.
Heptagenia longicauda
Heptagenia longicauda (Stephens, 1835), was previously known as H. flavipennis (Dufour). It was first recorded in Britain from the Kennet and Holybrook Canal near Reading in 1868. It has also been recorded at Staines in 1904 and by the River Wey between Tilford and Elstead, Surrey in 1933.
This species is clearly very rare, however it may be surviving overlooked in some watercourses. The current key to the nymphs of the British Ephemeroptera (Elliott, Humpesch and Macan, 1988) makes clearer the distinction between H. longicauda and H. sulphurea. The distinguishing feature used is the filamentous part of the gills. Unfortunately, the gills are often damaged during kick sampling. In Heptagenia longicauda, the filamentous part of the gills is as large as the flat plate in all gills (Figure 1) whereas, in H. sulphurea the filamentous part in some gills is smaller than the flat plate (Figure 2).
Arthroplea congener
Arthroplea congener Bengtsson, 1909 has only been recorded from the British Isles on one occasion. A single adult male was collected by R. South from Stanmore, Middlesex on the 4th June 1920. This record is now described as doubtful by many writers, and subsequently this species may not be included on future checklists of the British Ephemeroptera.
A. congener is distinguished immediately by its unique maxillary palp (Figure 3) and the lack of a tuft of filaments on all the gills.
If you require further information on either of these species or you think you may have found a specimen of Heptagenia longicauda or Arthroplea congener then please contact the Ephemeroptera Recording Scheme at the above address. Thank you for your assistance.