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Why Are There Tiny Flies Coming From My Drain?

Written by PestMan Editorial TeamTechnical review pendingPublished Updated

Quick answer

Small, fuzzy, moth-like flies resting near a shower, basin or laundry drain are drain flies. Their larvae live in the slimy organic film that builds up inside drains and traps. Scrubbing the drain with a long brush and hot water, and cleaning the strainer and overflow, removes the breeding site. If they keep coming back, check for a leak or broken pipe.

Why this happens

Drain flies lay eggs in the gelatinous film of soap, hair, skin and food residue lining pipes. The larvae feed in this film and the adults emerge into the room.

Drains that are used rarely, or have a slow flow, build up more film. Hidden leaks under showers or broken pipes under slabs can also create wet organic matter where drain flies breed.

What you may be seeing

  • Small grey, hairy flies with leaf-shaped wings on bathroom or laundry walls.
  • Flies that hop or flutter weakly rather than flying fast.

What you can do

  • Remove the drain grate and strainer and clean them thoroughly.
  • Scrub inside the pipe as far as you can reach with a long, flexible drain brush.
  • Flush with hot water; repeat every few days for a couple of weeks.
  • Clean basin and bath overflows, which also collect film.
  • Tape a clear plastic bag over a drain overnight to confirm which drain they come from.

What not to do

  • Do not rely on pouring chemicals down the drain; the film must be physically removed.
  • Do not pour insecticides into drains.

When professional help may be needed

If drain flies persist after cleaning, a plumber can check for broken pipes, leaks or poorly draining traps. That is often more useful than pest treatment.

Flies

Two-winged insects that breed in rotting organic matter. House flies, blowflies, vinegar flies and drain flies each point to a different breeding source, and finding that source is the key to getting rid of them.

Species mentioned

Drain Fly (Moth Fly)

Family Psychodidae

Small, fuzzy, moth-like flies that breed in the organic slime lining drains and appear on bathroom and laundry walls.

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Sources & further reading

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