In search of Sandy River Flies
The areas of sand and bare stone at the edge of rivers are referred to as Exposed Riverine Sediment – or ‘ERS’. This unusual habitat has been recently shown to support unique and diverse communities of rare beetles, but this is not the only reason these areas are important.
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| Southern silver stiletto-fly © Steve Hewitt |
In hot pursuit of three flies listed on the UK Biodiversity Action Plan, Buglife secured funding from Natural England, The Environment Agency, SEPA and the John Lewis Spedan Trust Fund, to investigate the fly fauna of this poorly understood habitat.
Unique and Rare Flies
Two of the Biodiversity Action Plan (BAP) flies are ‘stiletto’ flies (Therevidae): the ‘Southern silver stiletto-fly’ (Cliorismia rustica) and the ‘Northern silver stiletto-fly’ (Spiriverpa lunulata). These are moderately large, furry flies, and are easily recognised by the silvery males which glitter as they dance in the sunlight.
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| Southern silver stiletto-fly larva © Steve Hewitt |
Their larvae are less flamboyant and are long, thin, white and worm-like; they are ferocious predators with a glossy hard skin that lets them slither through dry sand as they chase their insect prey. The third species the project is studying is a rare cranefly Rhabdomastix laeta whose larvae live in the shallow water at the edge of sandy streams and rivers.
The Survey
From 2005 to 2006, consultants Martin Drake, Andy Godfrey, Steve Hewitt and John Parker surveyed 18 rivers all over the UK and stiletto-flies were found several times. Greatly expanding the area where stiletto-flies were previously known to occur and providing numerous new records. For the Southern silver stiletto-fly new sites were found on the Wey, Rother and Tay and they were recorded for the first time in Scotland! The Northern silver stiletto-fly was found to be numerous and widespread on the Spey and Tay in Scotland, and outside of Scotland there were new records for the rivers Lune, Coquet, Till and Beamish. A link to the survey report is provided at the bottom of this page.
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| River Rye © Roger Key |
Taxonomic confusion
The BAP cranefly Rhabdomastix laeta after further research actually turned out to be two species! Consequently all previous records masquerading under this name were actually for a different cranefly species japonica. However, the true laeta was found for the first time in Britain on a sandy Devon river in 2004, confirmed by a Buglife survey in 2005. For more information on the research done by Andy Godfrey, see links below to his report and the appendices:
Rhabdomastix Report 2007 and Additional Appendices
The Future
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| River Rother © John Feltwell |
These are just the tip of the iceberg of flies associated with sandy rivers; however this survey has provided a starting point for future research. This initial survey has shown ERS to be rich in fly species with 850 species recorded, 87 of which were nationally rare or scarce species, with six species that are new to Britain, see the report below for more information.
Click here for a copy of the 'Fly Assemblages of Sandy Exposed Riverine Sediment' (9MB pdf.)
As a direct result of Martin Drakes' survey work he published three papers in the 'Dipterist Forum', on three new fly species to Britain: Rhaphium suave, Hilara tenella and Hilara aartseni. See a link to the papers below:
Three new fly species to Britain
The continuing work of Buglife and others on this habitat is revealing a whole new field of study and highlighting pressing conservation issues. Further information on Buglife's involvement in riverfly conservation can be found by clicking here.
