PestControlBasics
Menu

Identify

Treat

Local

About

Drain Fly (Moth Fly)

Psychodidae (shown: Clogmia albipunctata)[6][2]

Drain flies, also called moth flies or filter flies, are small, fuzzy, non-biting flies whose larvae live in the slimy film inside drains, toilets and other places where water stands.[1][2][3]

Group
Insect
Order
Diptera
Family
Psychodidae
US records
48 states
Sources
6 cited
Updated
2026-10-06
Adult drain fly (moth fly), fuzzy with wings held roof-like
Adult drain fly (moth fly), fuzzy with wings held roof-like. (c) Katja Schulz, some rights reserved (CC BY) — via iNaturalist, CC BY 4.0
On this page
  1. Identification
  2. Look-alikes
  3. Where it lives
  4. Biology
  5. Damage and signs
  6. Health risk
  7. Control
  8. Telling small indoor flies apart
  9. Related profiles
  10. Common questions
  11. Sources

How to identify it

  • Adults are about 1/16 to 3/16 inch long and dark, with bodies and broad, leaf-shaped wings covered in fine hairs, giving a fuzzy, moth-like look.[2][3]
  • At rest the wings are held roof-like over the body; they sit on walls near drains and make short, hopping flights.[1][2][3]
  • When swatted or mashed, they disappear in a cloud of fine dust from their wing scales.[1]
  • Larvae are small, slender and gray and can sometimes be seen wriggling in the water film.[1][3]

Look-alikes

Look-alikeHow to tell them apart
Fruit flyTan with red eyes, not fuzzy, and breeds in fermenting food.[4][2]
Fungus gnatSlender, dark and mosquito-like, staying near moist potting soil.[2]
Phorid flyHumpbacked and runs rapidly over surfaces when disturbed; breeds in decaying matter, leaking sewage and even dead animals.[2]

Where it lives

Indoors they breed in sink, shower, tub and floor drains, little-used toilets, and refrigerator drain pans; outdoors in low wet spots such as air conditioner drainage and clogged gutters. They can also signal a broken sewer line.[1][3]

US map: public records from 48 states since 1990 (GBIF).

Biology and life cycle

Females lay clusters of 10 to 100 eggs on gelatinous organic films; eggs hatch in about 48 hours at around 70°F.[2][1]

The life cycle takes about 10 to 15 days at 70°F and can continue year round indoors.[1]

Larvae feed on decaying organic matter, bacteria, algae and fungi in the water film, and can trap air bubbles to survive submerged for a day or more.[2][1]

Damage and signs

  • Few flies after a trip usually means a temporary problem that ends once water flows normally again; many flies over several weeks means a persistent breeding site.[1]

Health risk

Drain flies don't bite or transmit disease directly, but because they breed in filth they could carry bacteria.[2][3]

Control

Sanitation

Scrub the slime out of drains and traps with a stiff brush; an enzyme or biological drain cleaner helps break down the film.[1][2][3]

Boiling water, bleach or chemical drain cleaners alone don't solve the problem, and insecticides should not be poured down drains.[3][1]

Traps and physical control

Find the source: tape (sticky side down) or an inverted clear cup lightly coated with oil or petroleum jelly over a drain for a few days will catch emerging adults.[1][3]

When to call a professional

If flies persist with no source in drains, suspect a sewer line break under the floor; confirming it may require opening the floor or slab.[3]

Telling small indoor flies apart

Fruit flies: tan with red eyes, around ripe or fermenting food, trash and recycling. Fix: remove the fermenting source.[2][4]

Fungus gnats: slender, dark and mosquito-like, near houseplants. Fix: let potting soil dry and remove organic debris.[2][5]

Drain flies: fuzzy, moth-like, on bathroom and kitchen walls. Fix: scrub out drain slime.[2][1]

Phorid flies: humpbacked, run before flying, around garbage, drains and decaying matter. Fix: find the decaying source, which can be hidden.[2]

Common questions

Will bleach get rid of drain flies?
No. Bleach, boiling water and chemical drain cleaners aren't effective; scrubbing out the slime layer is.[3]
Why do drain flies show up after vacation?
They develop in standing water in little-used drains and toilets; normal water use usually ends a small infestation.[1]

Sources

  1. University of Kentucky Entomology, “ENTFACT-615: Drain Flies or Moth Flies.” entomology.mgcafe.uky.edu/ef615 (accessed 2026-10-06)
  2. University of Kentucky Entomology, “ENTFACT-657: Small Flies.” entomology.mgcafe.uky.edu/ef657 (accessed 2026-10-06)
  3. University of Minnesota Extension, “Flies (reviewed 2024).” extension.umn.edu/garden-and-home/home-maintenance/household-insects/flies (accessed 2026-10-06)
  4. University of Kentucky Entomology, “ENTFACT-621: Fruit Flies.” entomology.mgcafe.uky.edu/ef621 (accessed 2026-10-06)
  5. University of California Statewide IPM Program, “Pest Notes: Fungus Gnats, Publication 7448 (August 2013).” ipm.ucanr.edu/legacy_assets/PDF/PESTNOTES/pnfungusgnats.pdf (accessed 2026-10-06)
  6. iNaturalist, “Clogmia albipunctata taxon page (order and family).” www.inaturalist.org/taxa/258813 (accessed 2026-10-06)

Updated 2026-10-06. Built from sourced records. Spot an error? Tell us.