Fungus Gnats - School IPM - USU Extension

    Fungus Gnats

    Sciaridae; Fungivoridae

    fungus gnat

    Adult fungus gnat (Johnny N. Dell, Bugwood.org)

    Fungus gnat

    Adult fungus gnat (Whitney Cranshaw, Colorado State University, Bugwood.org)

    Fungus gnat

    Fungus gnat larvae (Whitney Cranshaw, Colorado State University, Bugwood.org)

    Identification

    • smaller, dark, delicate-looking flies similar in appearance to mosquitoes
    • light gray to clear wings
    • long, slender legs
    • segmented antennae

    Nesting Habits

    • eggs and larvae nest in soil/moist organic material
    • usually originate from soil in potted plants
    • can develop in soil or mulch outside of building
    • attracted to light (e.g., windows and exterior lighting)

    Diet

    • larvae feed on fungi in soil, potting mix, mulch, etc.

    Significance

    • flies inside are a nuisance
    • when present in large numbers, larvae can damage roots and stunt growth of seedlings and young plants

    IPM Recommendations

    • Locate breeding susbstrate and remove or alter.
    • Do not overwater plants.
    • Let soil in potted plants dry out between watering.
    • Keep exterior doors closed, install screen doors, or install automatic door closers.
    • Exclude fly entry via caulking, weather stripping, door sweeps, screens, etc., especially around windows and doors.
    • If flies are coming from outside, consider changing exterior lighting to sodium vapor lighting.
    • Use nematode-based insecticides (e.g., Gnatrol) on soil of affected potted plants.

    Additional Resources

    Fungus Gnats in the Home fact sheet

    IPM for Flies: Integrated Pest Management in Sensitive Environments (University of Nebraska-Lincoln Extension)