University of Maryland Extension

Fungus Gnats

fungus gnat close up


Fungus gnats are tiny, black flies that are commonly seen around lamps and windows. They are annoying but harmless. The larvae breed in moist soil, primarily in potted plants containing soil rich in organic matter. Larvae feed on fungi in the moist soil. Over watering contributes to the growth of the fungi on which the larvae feed.


To control fungus gnats, determine if the gnats are coming from a particular plant or drain. To do this, cover the plant or drain with screen or cheesecloth and check the next day for evidence of the flies. If the fungus gnats are breeding in potting soil, dry it out. When the soil dries, the larvae will die. Change the watering cycle of the house plants to prevent the soil from remaining wet. If they are breeding in a drain, use a commercial drain cleaner and or clean out the trap to eliminate the breeding site.

Picture of Larva of a fungus gnat. 
Larva of a fungus gnat


Dark Winged Fungus Gnats PictureDark Winged Fungus Gnats

A very unusual insect occurrence may be noticed during wet years, near wooded areas or even crossing a driveway. These insects are a species of dark winged fungus gnat larvae. These and related species have this interesting habit of moving in snake-like masses. The larvae are harmless and live in decomposing organic matter in wooded areas.

Photo: S. Klick, UME-IPMnet


Maintained by the IET Department of the College of Agriculture and Natural Resources. © 2019. Web Accessibility