Conisternum obscurum
A small greyish species with a reddish frons and face. Legs reddish yellow. Halteres yellow. Wings clear with yellow veins. Palps rather long, somewhat flattened and yellow. Antennae with second segment pale, but otherwise dark. Wing length: ♂ 4.1 - 5.0 - 6.0 mm (6); ♀ 4.1 - 4.2 - 4.3 mm (5).
Berté & Wallace (1987)[1] describe the biology of this species in Ireland. The larvae are aquatic and were found in the egg masses of Limnephilid caddis flies in stony streams and rivers. Larvae moved around within the jelly of the egg mass and fed on eggs they encountered by slashing through the chorion with their mouth hooks. Occasionally they protrude their prominent posterior spiracles through the surface of the jelly for a short time. Larvae left the egg mass to pupate and, in no case, were all the eggs in an egg mass consumed. Adults are usually swept from long vegetation beside such water bodies in June to August.
This appears to be a scarce but widespread species in northern and western Britain.
World distribution: Palaearctic: Belgium, Czech Republic, Denmark, Estonia, Finland, France, Germany, Ireland, Netherlands, Norway, Poland, Slovakia, Sweden, Switzerland; Russia: north European and Eastern Palaearctic; Asia: Mongolia.