Riverfly Census uncovers rare mayfly species: Brown May Dun

The Brown May Dun (Heptagenia fuscorgrisea)

As a result of our species level monitoring of riverfly life as part of our groundbreaking Riverfly Census, the highly elusive brown may dun Heptagenia fuscogrisea has recently been discovered in both the Usk (at Great Hadwick) and the Ribble (at Long Pool).

brown may dun

Significant Discovery

The rare brown may dun has a conservation status of Nationally Notable and is incredibly elusive and localised.

It is occasionally found in Dumfries, Galloway, Thames Catchment and in Ireland; but this is the first reported sighting on both the Ribble and the Usk, and possibly in Wales.

The discovery is significant due to the rare and elusive status of the brown may dun, coupled with it's susceptibility to stressors in the water which make it an excellent indicator species.
The S&TC River Fly Census is as much about protecting the habitat for these rarities and the wild fish who rely on them, as it is about highlighting and then tackling the EA over declining water quality.


Below: Brown May Dun information
brown may dun


Riverfly Census: species level monitoring

We welcome the news and are proud of the discovery, made by our commissioned independent scientist, Dr Nick Everall.

The  elusive brown may dun represents something very positive among the largely damning findings of our Riverfly Census. Yes, much work is needed to secure and enforce better protection for our rivers; but amidst this we find that our bugs are resilient little critters who continue to surprise us.

Furthermore, our high-level monitoring is proving itself a worthy and necessary investment in the work to understand and thereby better protect our waters. Without species-level analysis, this discovery would not have been made.

Indeed, this discovery promotes the power and importance of species level benchmarking for effective and professional monitoring, which is the crux of our work. We cannot (and will not) proceed without robust and in-depth scientific evidence.


Brown may dun & our River Invertebrate App

The rare brown may dun has been added to our unique river invertebrate app, an important resource for anglers, scientists, nature lovers and anyone interested in the life and health of their local river.

Using high quality digital images (produced by Dr Cyril Bennett MBE), the river invertebrate app shows easily identifiable features for each species, plus its pollution fingerprint and conservation value.

Rather than forking out for an expensive identification key or field guide, carrying it on the river bank, and needing to re-purchase when it becomes out of date; or app is an easily accessible, simple to use, and constantly updated resource which does the job for you.

Find out more about the River Invertebrate App.

brown may dun

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