Riverflies

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. Go to the 'Anglers Riverfly Monitoring Initiative (ARMI)' page of this website 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.

More than 270 species of mayflies, caddisflies and stoneflies have been recorded in the UK, eight of which 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.

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'.

Reported apparent declines in riverfly numbers are of increasing concern whilst the factors that may cause a detrimental impact to riverfly populations are numerous, including:

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 runoff, 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 riverfly 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 Mayfly

Plecoptera 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

Questions on riverflies

If you have specific questions concerning riverflies contact Craig Macadam from the Riverfly Recording Schemes via email info@ephemeroptera.org.uk.