What are the small flies resting on bathroom walls?
What are the small flies resting on bathroom walls?
The small flies that rest motionless on bathroom walls are drain flies, also known as moth flies.
Characteristics of drain flies
Drain flies are easy to identify with several distinct features:
- Very small (about 2-3 mm), appearing more "stocky" than fruit flies.
- Bodies and wings covered with fine hairs, giving a fuzzy appearance.
- Wings are broad and oval; when resting on walls, they look like a small cloak covering the body.
- Color is grayish-brown or light gray.
- Poor fliers; they often move in short, jerky hops along walls.
Why do they appear in bathrooms?
Their presence indicates that larvae are breeding in the drain or floor trap. Larvae live in the organic sludge on the inner walls of drainpipes and bends, feeding on grime and microorganisms. Adults emerge from the drains and rest on walls — so what you see are adults; the real problem is in the pipes.
Difference from fruit flies
- Drain flies: fuzzy, round wings like moths, rest on walls, appear in bathrooms.
- Fruit flies: red eyes, smooth body, fly actively in the air, appear near kitchen garbage.
How to deal with them?
Since drain flies come from the drains, the core treatment is cleaning the pipes:
- Use a brush to scrub the inner walls of the floor drain.
- Pour a pot of boiling water down the drain to kill eggs and larvae.
- Replace the floor drain with an insect-proof type (with spring or magnetic seal) or install a drain insert.
- Spray dinotefuran-containing household insecticide on bathroom walls and around drains to kill adults.