University of Maryland Extension

Fungus Gnats - Houseplants

close up of fungus gnat

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. Overwatering contributes to the growth of the fungi on which the larvae feed.

close up of fungus gnat larva
Fungus gnat larvae

microscopic fungus gnat larva
Fungus gnat larva

Management

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 houseplants 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. 

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