• Size: Small to tiny flies; range from one millimeter to one-fourth inch in length.
  • Color: Most species are black, some brown; have very long thin legs and wings.
  • Behavior: 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. The tiny flies flitting about one’s personal workspace can be disconcerting, prompting calls to have the insects controlled.


In nature, fungus gnats breed in the soil, in fungi, and any place where suitable molds 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, molds 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. Molds 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 molds, thus eliminating the breeding media used by the flies.

  • 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.