Sandy River Flies

In search of 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.

In hot pursuit of three engaged and declining flies listed on the UK Biodiversity Action Plan, Buglife secured funding from Natural England, The Environment Agency, Scottish Enivoronmental Protection Agency (SEPA) and the John Lewis Spedan Trust Fund, to investigate the fly fauna of this poorly understood habitat.

Unique and Rare Flies

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. Another stiletto fly that was previously on the BAP list, is the 'Northern siliver stiletto-fly' (Spiriverpa lunulata). However, due to more detailed surveys (including the Buglife survey) and information gathered on its numbers and locations in the UK this species was removed from the BAP list

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 fly 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 of sandy river flies

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.

In 2007 and 2008 a detailed survey was completed on the river shoals - ERS - in Cheshire by Steve Hewitt and John Parker. 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 its' future conservation, see link to report below.

River Rye © Roger Key

Taxonomic confusion

The BAP cranefly Rhabdomastix laeta after further research 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

Buglife publications on ERS and habitat surveys

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. Here is a link to those papers: Three new fly species to Britain

To learn more about Buglife's work on the Southern silver stiletto fly in Cheshire, see Steve Hewitt's and John Parker's report 'Distribution of stiletto fly Cliorismia rustica on Cheshire rivers ' for a copy of this report please click here

In 2008/9 Buglife completed another piece of work on the important invertebrates that live on river shores. This project looked at developing a means 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. For more information on this click here to see our report 'ERS invertebrate habitat survey of the rivers Eden in Cumbria and Irwell in Lancashire'.

We also produced an initial report looking at assessing gravel extraction in the North West entitled 'Impact of gravel extraction on ERS invertebrate communities on the river Eden in 2008 - Pilot study' for a copy click here. All this work was undertaken by Steve Hewitt and John Parket and was funded by the North West Enivornment Agency.

River Rother © John Feltwell

The Future

These surveys 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. Further information on Buglife's involvement in freshwater conservation can be found by clicking here.