River Sands and Shingle

River sand and shingles create sandy rivers are a surprisingly rich but neglected habitat. At first glance the banks and islands of bare stones and sand that skirt river edges appear to be devoid of life, however, closer inspection reveals them to be rich in rare flies and beetles.

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

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.

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