Description of fungus gnats
Fungus gnats are very common, small, non-biting flies that normally go unnoticed. They are completely harmless, except they are an annoyance by their presence. Fungus gnats are frequently quite plentiful outdoors in fungi, damp soil and decayed vegetable matter. Though fungus gnats occasionally wander in from outdoors, a persistent problem with this nuisance in the house indicates an indoor breeding site. The immature stage of the fungus gnat is a small white maggot that lives in very moist areas high in decaying organic matter. This habitat may occur indoors with houseplants or in slow-running drains, moisture-accumulating cracks and crevices, refrigerator drain pans, and other places where fungi and slime accumulate.
Damage caused by fungus gnats
When houseplants are infested, it is often because they are overwatered. Fungus gnats cannot survive in houseplants if the soil is permitted to dry out almost to the leaf-wilting point between waterings. Otherwise, houseplant insecticide spray can be applied to the surface of the soil and around the edges of the pot.
Management of fungus gnats
Indoor household insecticide aerosols can be used to control the adult gnats. However, this treatment has to be repeated to catch all of the gnats as they emerge and does not usually result in complete control. Controlling the maggots by locating and eliminating the breeding site gives the best results.
Sources of maggots other than houseplants (drains, water-soaked areas, etc.) should be cleaned or dried. In the case of slow-moving drains, physically cleaning the drains with a stiff brush will be of more benefit than chemical drainer openers.
Do you live in Iowa and have an insect you would like identified?
The Iowa State University Plant & Insect Diagnostic Clinic will identify your insect, provide information on what it eats, life cycle, and if it is a pest the best ways to manage them. Please see our website for current forms, fees, and instructions on preserving and mailing insects.
Contact information for each states diagnostic laboratory for U.S. residents. If you live outside of Iowa please do not submit a sample without contacting the Plant & Insect Diagnostic Clinic.