WSU Extension


Moth flies (drain flies)

(revision date: 7/30/2015)

Use Integrated Pest Management (IPM) for successful pest management.

Moth flies (sometimes called drain flies) are small hairy moth-like dipterans (true flies) in the family Psychodidae. As a group, they don’t get much larger 5 mm (about 1/5 inch) long. The small larvae are aquatic and their legless bodies end with an obvious breathing tube. The adult flies have the habit of holding their wings roof-like over their bodies. In nature they are often found in shady places along streams with decaying waste material or around sap emanating from trees. When found in human habitats, they develop in decaying organic debris in sewage beds, compost, septic tanks, or filthy garbage containers. In homes they emerge from the drains of sinks, bathtubs, or shower stalls where bacteria, fungi, and sludge have accumulated. In nature they are considered beneficial recycling organisms. In human habitats, most species are merely a nuisance. Occasionally, when adult numbers become excessive, they have been implicated in cases of inhalant allergy.
Management Options

Non-Chemical Management
  • Do not allow moist organic debris to accumulate in or around the house. Keep garbage pails dry and clean.
  • Keep the drains in bathtubs, sinks, and shower stalls clear from build-up of sludge.
  • Biological drain cleaners (non-toxic) can be used to remove the organic slime layer and organic debris in the drain.
Select non-chemical management options as your first choice!

Chemical Management

None recommended. If you can not manage your moth fly problem contact a licensed pest management professional.

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Caption: Drain fly or Moth fly
Photo by: Ken Grey