What are drain flies?

Drain flies (also known as moth flies, sewer flies, family Psychodidae) are tiny flying insects commonly found around bathroom and kitchen drains.

Their bodies are about 2–5 mm long, and their bodies and wings are covered with fine, dense hairs, giving them the appearance of miniature moths — at rest, their wings are held roof-like over the body.

Drain fly larvae live in the organic buildup inside drain pipes (soap scum, grease, hair, food debris, and the biofilm of bacteria and fungi) — they feed on this sludge.

After emerging from the drain, adults usually rest motionless on nearby walls; their flight is weak and slow.

Drain flies do not bite or transmit diseases, but large numbers of them indicate a serious accumulation of organic matter in the drain that needs cleaning.

Treatment methods: ① Physical cleaning — use a pipe brush to scrub the organic buildup from the inner walls of the drain (this is the most effective method).

② Boiling water flush — pour a large pot of boiling water down the drain once a day for a full week.

③ Baking soda + white vinegar — pour into the drain, let it foam for 15 minutes, then flush with boiling water.

Do not pour insecticides or bleach down the drain — they will not kill the larvae and eggs inside the pipe, and bleach can corrode metal pipes.