University of Maryland Extension

Drain Flies

close up drain fly

Key Points

  • Drain flies are found primarily in rooms or areas where there are drains - kitchens, bathrooms, and basements  near floor drains, etc.
  • Drain flies are small, 1/16 to 1/4 inch long, delicate and fuzzy. They are pale brownish-gray to black. The larvae live in the gelatinous film or slime in drains and traps. They feed on algae, bacteria, and fungi in the slime.
  • They may also breed in areas of sewer leaks and back-ups, dirty garbage cans, saucers under potted plants, clogged storm drains, and in condensate pans under refrigerators and air conditioners.
  • Adult flies may live up to 2 weeks and total development time from egg to adult may take 7 to 28 days.
  • Flies emerge daily once an infestation is underway.
  • Fungus gnats can also breed in drains. 


  • Clean traps and drains mechanically or with an over-the-counter drain cleaner followed by hot water. Clean or eliminate breeding sites. 

Rev. 2020

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