Drain flies (also called moth flies or sewer flies) are tiny, fuzzy, moth-like flies that rest with their wings covering the body. Maryland Extension describes adults as about 1/16 to 1/4 inch long, pale brownish-gray to black. They are poor fliers and often hop or make short flights near sinks, showers, floor drains, and other damp sites.
Adult appearance
- Size: roughly 1/16–1/4 inch long (Maryland Extension).
- Body: delicate and fuzzy / hairy-looking.
- Color: pale brownish-gray to black.
- Wings: broad; held tent-like over the body at rest.
- Flight: weak; hopping is common.
Source: Maryland Extension — Drain Flies. ID overview: Maryland Extension — Identifying common household insect pests.
Larvae and breeding film
Larvae live in the gelatinous slime film inside drains and traps, feeding on algae, bacteria, and fungi. They may also develop in sewer leaks, dirty garbage cans, plant saucers, clogged storm drains, and condensate pans. Adults may live up to about two weeks; egg-to-adult development can take roughly 7–28 days (Maryland Extension).
Focus on finding and cleaning the moist organic film.
Look-alikes
- Fruit flies: often tan with reddish eyes; tied to fermenting food and recycling—see Maryland Extension fruit flies.
- Fungus gnats: slender, mosquito-like, often near damp potting soil; Maryland notes they can also breed in drains with moist debris—see aphids vs fungus gnats and fungus gnats with no plants.
What to do once you identify them
Clean traps and drains mechanically; clean or eliminate other breeding sites. Do not rely on DIY disinfectant pastes mixed from household cleaners—see corrected guidance in gnats in the drain.
Source: Maryland Extension — Drain Flies.
FAQ
Where do I find them? Kitchens, bathrooms, basements near floor drains, laundry rooms, and other damp organic sites.
Are they the same as fungus gnats? No—different shape and usual breeding sites, though both can involve moisture.
