Window Gnat, window fly (Sylvicola fenestralis)



The large numbers of these flies which can emerge from pupation areas means that these flies can
 constitute a nuisance in domestic premises where they are often found, as their common name implies, on
 the windows.

Control of window gnats

If a single specimen is found then treatment would not be necessary, however, if swarms of flies are present
 then an attempt should be made to locate the larval breeding sites and eliminate them if possible. We deal effectively and efficiently with swarms of adults by using a space spray of insecticide.

An approved formulation must be used for controlling this species at sewage works to prevent contamination of the water supply. For advice about this or other pest species call CSS pest control on  0800 254 5003.

Key features

Adult fly is 6 – 7 mm in length with a wing span of
 15 -17 mm. The fly is predominately dark
 brown with a light striped appearance. The wings are strongly veined and there are brown
 shaded areas in the membranous zones of the
 wings with a particularly dark patch on the leading
 edge of the wing.


Adult females lay their eggs, in a complex egg mass, in wet areas rich in organic matter. These flies are
 commonly found at sewage works.

The larvae which emerge are essentially aquatic, feeding on organic matter.

Having pupated in their aquatic environment the adults emerge and are typically found in distinctive 

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