Images from left: Up-wingfly Ephemera danica © Mark Pike NIW prize winner; Stonefly Perlodes microcephala © David Pryce; Caddisfly Limnephilidae species © Emma Ross
Riverflies: Mayflies (Ephemeroptera or up-wing flies), caddisflies (Trichoptera) and stoneflies (Plecoptera)
The Riverfly Partnership interest focuses on three key groups of riverflies: the up-wing flies or mayflies (Ephemeroptera), caddisflies or sedges (Trichoptera) and stoneflies (Plecoptera) in whatever habitats they occur (rivers and still waters).
Riverflies, along with other freshwater invertebrates, are at the heart of the freshwater ecosystem and are a vital link in the aquatic food chain. Their common characteristics of limited mobility, relatively long life cycle, presence throughout the year and specific tolerances to changes in environmental conditions make them good biotic indicators of water quality and useful indicators of change in local environmental conditions. See Anglers Monitoring Initiative for further information on how angling (and other interested) groups are playing an instrumental role in protecting the health of their local rivers by monitoring their riverfly populations.
There are a total of 278 species of mayflies, caddisflies and stoneflies, of which eight species have Biodiversity Action Plan status and therefore are recognised as of priority for conservation by the government.
For further information on these riverfly groups see also the Riverfly Recording Schemes pages hosted by the Biological Records Centre.
Riverflies - the canary of our rivers
The health of a river is dependent on many factors, three primary ones being water quality, habitat and flow. Riverfly populations reflect the health of our rivers and still waters. They are sensitive indicators of water quality and commonly referred to as the rivers 'canary'.
The Angler's Monitoring Initiative is a Riverfly Partnership project where trained volunteer groups monitor the water quality of their rivers by recording the abundance of riverfly groups. Should abundances fall below a site specific level the groups alert the relevant statutory body for further investigation. The initiative, launched in 2007, has already led to three successful Environment Agency prosecutions of the companies responsible for the falls in water quality first detected by the volunteer groups.
Reported apparent declines in riverfly numbers are of increasing concern.
Factors that may cause a detrimental impact to riverfly populations, include, amongst others:
Habitat loss
Many ponds have been lost in recent years through in-filling, draining or natural succession. Modification of river channels e.g. straightening, causes the loss of critical bank-side and shallow in-stream habitat.
Point source and diffuse pollution
Agricultural run off, high in nutrient levels
Excess nutrients may also lead to large algal growths which smother vegetation and reduce dissolved oxygen levels creating unfavourable conditions for riverflies. The impact of insecticides on aquatic-invertebrates is demonstrated in that a teaspoon full of the pesticide cypermethrin can devastate all life to the volume of water equivalent to an Olympic size swimming pool.
Siltation
Soil erosion may lead to unnaturally high levels of silt in watercourses which smother the river bed
Low flows as a result of climatic causes or abstraction. Reduced flow can reduce habitat availability and cause pollutants to become more concentrated.
Climate change & temperature variation
Light pollution
Artificial light may cause disorientation in adult riverflies attracting them away from their natural bankside habitat.
Biodiversity Action Plan riverfly species
Eight species of riverfy qualified for conservation status on the new Biodiversity Action Plan Species list. Inclusion on the list means that there is government commitment to support conservation measures for these species. The riverfly species included are:
Ephemeroptera Nigrobaetis niger Southern Iron Blue, Potamanthus luteus Yellow MayflyPlecoptera Brachyptera putata Northern February Red, Isogenus nubecula Rare medium stonefly
Trichoptera Glossosoma intermedium Small Grey Sedge, Hagenella clathrata Window Winged Sedge, Hydropsyche bulgaromanorum Grey Flag, Ironoquia dubia Scarce Brown Sedge
For further information see here.
The Riverfly Partnership are carrying out a three year project to increase our knowledge of the Biodiversity Action Plan riverfly species in England, with funds granted through Natural England Countdown 2010. The project includes surveys and conservation action.
Images from left: Baetis niger © Stuart Crofts; Hagenella clathrata © Matthew Wallace; Isogenus nubecula © Mike Hammett
Riverfly articles
Articles by Peter Barnard, Scientific Director of the Royal Entomological Society and former Research Entomologist specialising in Trichoptera, on the History of fishing flies and the Swarming of riverflies published in Salmo Trutta (2005 pp.58-59 & 2006 pp.69-72 respectively) are available here by kind permission of The Wild Trout Trust.
» Riverfly swarming by Peter Barnard – PDF-File, 982.7 KB
» Brief history of fishing flies by Peter Barnard – PDF-File, 2.0 MB
Grannom hatch © John Levell
Questions on riverflies
If you have specific questions concerning riverflies contact Craig Macadam from the Riverfly Recording Schemes via email info@ephemeroptera.org.uk.
