Stiletto fly (Cliorismia rustica)

Chorisima rustica specimen
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Stiletto fly fact file

Stiletto fly description

GenusCliorismia (1)

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

Psilocephala rustica.
Length: 10-11 mm (2)

Stiletto fly biology

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).


Stiletto fly range

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).


Stiletto fly habitat

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).


Stiletto fly status

Classified as Rare in Great Britain (3).


Stiletto fly threats

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).


Stiletto fly conservation

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).


Find out more

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:



In arthropods (crustaceans, insects and arachnids) the abdomen is the hind region of the body, which is usually segmented to a degree. In crustacea (e.g. crabs) the limbs attach to the abdomen; in insects the limbs are attached to the thorax (the part of the body nearest to the head) and not the abdomen. In vertebrates the abdomen is the part of the body that contains the internal organs (except the heart and lungs).
Stage in an animal's lifecycle after it hatches from the egg. Larvae are typically very different in appearance to adults; they are able to feed and move around but usually are unable to reproduce.
Part of the body located near the head in animals. In insects, the three segments between the head and the abdomen, each of which has a pair of legs.


  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):

Image credit

Chorisima rustica specimen  
Chorisima rustica specimen

© The Natural History Museum, London

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United Kingdom
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Fax: +44 (0) 207 942 5443


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