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)