Fungus gnats are small, short-lived (7 to 10 days) flies whose larvae–depending on the species–feed on detritus and/or plant roots and/or fungi, thereby contributing to the decomposition of organic matter. The adults are only 2–5 mm long but are nevertheless important pollinators for both plant pollen and mushroom spores. Fungus gnats are often a nuisance indoors, however, where their numbers can quickly build (depending on the severity of the infestation), hatching out from potted plants or containers with damp soil that is rich in organic matter. Their eggs are deposited in the soil and the entire life cycle from egg to adult can take as little as 20 days. The adult flies are fast and evasive fliers, making them difficult to squash in mid-air via clapping! They are attracted to lights, which can be particularly aggravating when they flit about on one’s TV/computer monitor or iPhone/tablet, etc. screen. For anyone who wears glasses at night, they will also be attracted to any spots of reflected light from the eyeglass lenses, bringing them in close to one’s eyes and face which can be extremely annoying.
The root-feeding that is done by some species of fungus gnat larvae can harm many plants, causing stunting and wilting (see the fact sheets below for more information and for management strategies you may wish to employ to reduce or eliminate their numbers). The larvae are also capable of transmitting certain soil-borne plant pathogens.
- Fungus Gnats (Ohio State University Extension)
- How to Control Fungus Gnats (University of Nebraska Extension)
- Dark-winged Fungus Gnats (a common family of fungus gnats) (BugGuide.net)