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| Southern silver stiletto-fly © Steve Hewitt |
Where can you find Sandy River Flies?
The shoals 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; they can support endangered and declining sandy river flies. Two associated flies are listed on the UK Biodiversity Action Plan (BAP).
Unique and Rare Flies
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| Southern silver stiletto-fly larva © Steve Hewitt |
One of the Biodiversity Action Plan (BAP) flies is a ‘stiletto’ fly (Therevidae): the ‘Southern silver stiletto-fly’ (Cliorismia rustica). This is a moderately large, furry fly, and is easily recognised by the silvery males that glitter as they dance in the sunlight.
Stiletto larvae 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 second BAP fly species is a rare cranefly Rhabdomastix laeta whose larvae live in the shallow water at the edge of sandy streams and rivers.
Good news!
Another stiletto fly, the 'Northern silver stiletto-fly' (Spiriverpa lunulata), was previously on the UK BAP list. Due to more detailed surveys (including Buglife surveys) and information gathered on its numbers and locations in the UK this species has now been removed from the BAP list.
Buglife’s Sandy River Flies Projects
In 2005 Buglife secured funding from Natural England, The Environment Agency, Scottish Environmental Protection Agency (SEPA) and the John Spedan Lewis Trust Fund, to investigate the fly fauna of this poorly understood habitat. Further funding from the Environment Agency and the Countryside Council for Wales has meant that Buglife has been able to continue increasing knowledge about the ERS habitat and associated invertebrate species through further surveys.
Surveys have 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 table below for a summary of the work done for the project so far.
Project time-line and achievements
| Year | Activity | Reports |
| 2005 | Research done by Andy Godfrey showed that the BAP cranefly Rhabdomastix laeta was two species. Consequently it was assessed that all previous records for this species were infact for a different cranefly species Rhabdomastix japonica. 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. Further research on this subject was done by Andy Godfrey. | Rhabdomastix Report 2007 Click here Additional Appendices Click here |
| 2005 - 2006 | Surveys were undertaken of 18 rivers all over the UK. Stiletto-flies were found several time, 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. 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. | Fly Assemblages of Sandy Exposed Riverine Sediment Click here Three new fly species to Britain Click here |
| 2007 - 2008 | A detailed survey was completed on the river shoals - ERS - in Cheshire. This survey found a number of new records for the Southern silver stiletto fly, indicating that Cheshire is a strong hold for the fly and the county is an important area for future conservation of this species. | Distribution of stiletto fly Cliorismia rustica on Cheshire rivers Click here |
| 2008 | We produced an initial report looking at assessing gravel extraction in the North West | Impact of gravel extraction on ERS invertebrate communities on the river Eden in 2008 - Pilot study Click here |
| 2008 - 2009 | In 2008/9 Buglife completed another piece of work on the important invertebrates that live on river shores. This project looked at developing a method of recording the characters of river shores and so assessing their ability to support important ERS invertebrates. As a result the quality of river shores for invertebrate could be easily assessed and monitored. | ERS invertebrate habitat survey of the rivers Eden in Cumbria and Irwell in Lancashire Click here |
| 2010 | Survey method developed in previous project assessed on high quality ERS sites in Wales | ERS invertebrate habitat survey of the rivers Afon Ystwyth and Afon Rheidol in Ceredigion – March 2010. Buglife. Click here |
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| River Rye © Roger Key |
The Future
The surveys so far have provided a starting point for future research into ERS habitats. The continuing work of Buglife and others on this habitat is revealing a whole new field of study and highlighting pressing conservation issues.
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| River Rother © John Feltwell |
To see the Sandy Riverflies project summary sheet click here.
For information on Buglife’s other freshwater projects click here or click on the links in the left hand panel.
