General
Dark brown/black in colour.  1.2-1.5mm long, with a wing span of around 3-4mm.
The wings have sparse venation with a number of darkly pigmented areas with prominent y-shaped cells in the centre and rear. They breed in water-logged soil, particularly in peaty soils.

Significance  
In the UK they are a major problem due to their habit of swarming in large numbers and inflicting many bites on humans.

Control
Little can be done to control development sites. Protection may be given by the use of insect repellents which should be applied during outdoor activity. Where swarms are seen, the localised use of a space spray of insecticide is effective. Routine ULV treatments of the room where the problem occurs will provide relief, along with fly screening of windows and doors.