Drain fly vs Fungus gnat

These two are easy to mix up. Here's how to tell a drain fly from a fungus gnat, and whether either one bites or stings.

Fungus gnat

Bradysia coprophila

Fungus gnats are more slender, longer-legged and have clear wings with visible venation; they are associated with potted soil rather than drains.

	Drain fly	Fungus gnat
To humans	Nuisance, allergen	Non-toxic
Size	2-5 mm long (body)	2-4 mm long
Colours	Dark grey, Light grey (hairy dusting), Brown (legs and antennae)	Black, Dark gray, Brown
Family	Psychodidae	Sciaridae
Habitat	Man-made wet habitats: sink and floor drains, sewage traps, septic tanks, drain pipes, grease traps, moist organic buildup in basements and boiler rooms.	Moist, organic-rich soils, potted plants, greenhouses, compost, decaying plant material
Range	Cosmopolitan in temperate and tropical regions, commonly found worldwide wherever indoor plumbing provides breeding sites.	Cosmopolitan in temperate regions; common wherever potted plants, greenhouses or decaying organic matter provide habitat
Active	Active year-round indoors; most active near dusk and at night. Outdoors in warm climates during spring-summer.	Year-round in heated greenhouses and indoors; spring to fall outdoors in temperate regions, most active in warm, damp conditions and at dusk
Pest?	Yes	Yes

Tiny (2-5 mm), densely hairy body and wings giving a fuzzy, moth-like look.
Broad, rounded wings held roof-like over the body with reduced wing venation.
Weak, fluttering flight; often walk or hop near drains rather than fly long distances.
Gather in groups on walls or near the drain where they breed, especially in bathrooms and kitchens.

Adults are 2-4 mm long, slender, dark-bodied flies with long legs and long multi-segmented antennae.
Larvae are white or translucent maggots with a dark head capsule, found in the top 1-3 cm of moist potting soil.
Adults are weak fliers and often seen walking on soil or flying low in swarms near plants or lights.
Species-level separation from other sciarids requires microscopic examination of adult genitalia; look for general sciarid morphology for field ID.

Fungus gnats are more slender, longer-legged and have clear wings with visible venation; they are associated with potted soil rather than drains.

Drain fly: Nuisance, allergen. Fungus gnat: Non-toxic. Drain flies do not bite or sting. Adults do not bite or sting.

Identification from photos is never certain: don't handle insects you can't identify, and get medical advice for bites, stings or allergic reactions.