Fungus Gnat

Family Name

Family Sciaridae





Small to tiny flies; range from 0.04 inch to 0.25 inch in length.


Most species are black, some brown; having very long thin legs and wings.


Fungus gnats are tiny flies that are simply annoying when found in buildings. Sometimes occurring in large numbers, they gravitate toward windows, attracted by sunlight, but may also fly about desks or be attracted to persons by cologne or perfumes. These tiny flies flitting about one’s personal workspace can be disconcerting, prompting calls to have the insects controlled. Gnats are non-biting Midges and are often mistaken for mosquitoes by their appearance.


In nature, fungus gnats breed in the soil, in fungi and any place where suitable moulds might grow, e.g., a rotting log. In buildings, they are most often associated with the soil in potted plants and in atriums. When plants are overwatered, moulds in the soil are capable of reproducing thus providing a breeding medium for fungus gnats. On occasion, these flies have been found breeding in ceilings and walls where water leaks are present or have occurred, but have not thoroughly dried. Moulds thrive in such damp areas and provide a place for fungus gnats (and certain fungus-feeding beetles) to breed.

Tips for Control

The control of fungus gnats involves discovering the breeding sites, then drying them out sufficiently to stop the growth of moulds and thus eliminating the breeding media used by the flies.

To minimize problems with flies, take the following steps:

 The top inch or so of the soil in potted plants can be turned over several times to dry out the soil.
 Plants should then be watered less frequently and only when watering is necessary. Soil in potted plants should not be allowed to stay constantly wet.
 Areas where water leaks have occurred should be dried thoroughly using fans, or wet wood or other building materials need to be replaced.