Pest Library
Fungus Gnat
Fungus gnats are tiny, dark, long-legged gnats that drift weakly around houseplants, windows and desks. Larvae feed on fungi and organic matter in constantly damp potting soil, so overwatering is nearly always the cause.
Profile
- Scientific name
- Bradysia spp.
- Identification
- Delicate dark body, long legs, mosquito-like silhouette but no biting mouthparts.
- Typical size
- About 1/8 inch (2-4 mm).
- Behavior
- Weak, erratic flight near soil surfaces and lit windows; adults are short-lived.
- Habitat
- Overwatered potted plants, interior planters, damp organic debris and wet crawl space soil.
- Diet
- Fungi and decaying organic matter in soil.
- Lifecycle
- Egg to adult in roughly two to four weeks in warm, moist soil.
- Why it matters
- A nuisance pest and, in offices and retail, a professionalism concern. Heavy larval populations can damage plant roots.
- DIY considerations
- Yellow sticky cards plus reduced watering resolves most cases without any treatment.
- Professional considerations
- Service confirms the moisture source, uses monitoring, and treats interior planters or damp areas where correction alone is not enough.
Signs of activity
- Gnats rising when a plant is watered or disturbed
- Gnats trapped at windows near planters
- Consistently wet potting soil surface
Prevention
- Let the top of potting soil dry between waterings
- Remove standing water in saucers and decorative planters
- Replace chronically infested soil and remove decaying plant debris
- Address crawl space and interior planter moisture
Sources
Related information
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