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Flies - (Drain Flies, Moth Flies, Sewer Flies)
Flies – (Drain Flies, Moth Flies, Sewer Flies)

Flies – (Drain Flies, Moth Flies, Sewer Flies)


  • Color: yellowish, brownish-gray, or blackish.
  • Size: adults – 1/16 to 1/4 inch long; larvae – 1/8 to 3/8 inch long.
  • Moth flies are very delicate and “hairy” flies with pointed, leaf-shaped, white-speckled wings held roof-like over their backs when at rest.
  • Larvae are long and cylindrical with the fore-end of the body somewhat flattened on the lower side which has eight suckers.

Habits of Drain, Moth, and Sewer Flies:

  • Females lay 30 to 100 eggs in the jelly-like film that line the water-free portions of drain pipes.
  • Developmental time (egg to adult): seven to 28 days.
  • Life span of adults: up to two weeks.
  • The larvae feed on algae, fungi, bacteria, and sludge.
  • Adult flies are poor fliers and are found in great numbers on walls or flying weakly in the area where they developed.
  • Adults are more active at night and are seen hovering near the breeding site; during the day they rest on vertical surfaces indoors and in protected areas outside.

Damage From Drain, Moth, or Sewer Flies:

  • Moth flies or drain flies become an annoyance within some structures when they breed in the liquids found in drains, dirty garbage containers, and septic tanks.

Look for:

  • Black slime in drains, broken drain pipes, e.g., no water in the trap, very moist accumulations of decaying organic matter, e.g., plugged or unused garbage disposal, dirty evaporation pan, e.g., dehumidifier, air conditioner, refrigerator, etc.

How to Control and Kill Drain, Moth, and Sewer Flies:

  • Infestations which develop in drains can be eliminated by scrubbing the area with a brush and sink-cleaning materials followed by very hot water. It is important to scrub the drain all the way to the trap.
  • If the drain trap is not holding water, it should be repaired. To prevent water evaporation in the trap of seldom-used drains, a small amount of vegetable or mineral oil should be placed on the surface of the trap water.
  • Large numbers of adult flies are easily controlled using a vacuum.

Innovative Pest Management serves the Washington, D.C., Northern Virginia, and Maryland area. Call us at (240) 755-0077 to schedule a free quote or appointment.