Fungus gnats are tiny black flies, frequently numerous in greenhouses and around certain house plants. Often called manure flies or mushroom flies, the adults do not feed on or damage plants. The larvae primarily feed on fungi and organic matter in the soil. Sometimes the maggots also feed on the roots of flower crops, especially poinsettias, geraniums, lilies, African violets and chrysanthemums. Heavy infestations cause plants to wilt, lose vigor, and drop their leaves. Larvae are pests because of the damage they cause to plants; adults are considered pests because they fly about the house in large numbers.
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Identification and Control Information
- Home & Garden Insect Series: Fungus Gnats as Houseplant and Indoor Pests (PDF)—Colorado State University Extension
- Utah Pests Fact Sheet: Fungus Gnats in the Home (PDF)—Utah State University Extension
- Structural and Public Health Pests: Flies (Drain flies, Fruit Flies, Fungus Gnats) (PDF)—University of Maine Cooperative Extension
[Photos, left to right: David Cappaert, Michigan State University, Bugwood.org; Whitney Cranshaw, Colorado State University, Bugwood.org; David Cappaert, Michigan State University, Bugwood.org]