Stiletto fly (Cliorismia rustica)

Synonyms: Psilocephala rustica
GenusCliorismia (1)
SizeLength: 10-11 mm (2)

Classified as Rare in Great Britain (3).

This stiletto fly has a greyish-black thorax. The abdomen is long and tapering, and is patterned with grey and black (2).

In Great Britain, this species is recorded predominantly from the Welsh Marches, including the rivers Usk and Monnow. It is also recorded from a few isolated sites in West Sussex and north-eastern Yorkshire. There have been very few new sites discovered in recent years despite increased recording effort, furthermore it seems that it has been lost from a few former sites (2). Although the European distribution is broad, the status of this fly is not clear (2).

Occurs around lowland rivers; adults inhabit sandy riverbanks where ridges of sand have formed. Alders or other trees and bushes are present to provide shade, but the species also appears to require bare sand in sunny areas (3).

Very little is known of the ecology of this species. The larvae of all stiletto flies are active soil predators, and it is presumed that those of Cliorismia rustica dwell in loose sand (3).

Main threats facing this species appear to include the removal of sands and gravels from rivers and their banks for use as aggregate, as well as deepening and canalisation of rivers, and water abstraction resulting in decreased river flow (3).

This stiletto fly is a UK Biodiversity Action Plan (UK BAP) priority species, and a Species Action Plan has been written in order to outline action required to conserve it, with the over-riding aim being the maintenance of all current populations (3). The organisation responsible for the delivery of these actions (the 'lead partner') is the Environment Agency. Future work on this fly will aim to determine the ecological requirements and distribution of the species more precisely, and to produce guidance on sympathetic river management (2).

For more on this species see the UK BAP Species Action Plan available on-line at:
For more on the Environment Agency see:

Information authenticated by the Environment Agency:

  1. National Biodiversity Network Species Dictionary (August 2002)
  2. Environment Agency (2000) Focus on biodiversity. The Environment Agency, Bristol.
  3. UK BAP Species Action Plan (August 2002):