Fungus Gnats - School IPM - USU Extension

    Fungus Gnats

    Sciaridae; Fungivoridae

    fungus gnat

    Adult fungus gnat (Johnny N. Dell,

    Fungus gnat

    Adult fungus gnat (Whitney Cranshaw, Colorado State University,

    Fungus gnat

    Fungus gnat larvae (Whitney Cranshaw, Colorado State University,


    • 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)


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


    • 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)