How to Get Rid of Drain Flies Indoors or Outside

Drain fly or Moth fly (Psychoda sp.)
Drain fly populations can explode quickly. Stavros Markopoulos/Moment/Getty Images

"Drain" flies can be a problem anywhere that standing waters, particularly around drains -- which is how this Moth fly (Psychoda sp.) got its common nickname. Though this small fly, which is often thought to be a fruit fly, causes no real damage, its high numbers can cause it to become a nuisance pest in or around the home.

Drain Fly Identification

Though it will likely take a magnifying glass to see all the specific characteristics of the drain fly, you may be able to see some of the following with just your eyes (or a pair of reading glasses):

  • It is 1/5 - 1/10-inch long.
  • Its body and wings are covered with long hairs that make it appear fuzzy and moth-like.
  • It has dark gray to black body and lighter colored wings.
  • Its antennae are long and curved.
  • It is also known as a drain fly, sewage fly or filter fly.

The Drain Fly "Hops"

Because it is a poor flyer, able to fly only a few feet at a time, you can identify the drain fly by its habit of making short, hopping flights when disturbed, rather than flying a distance. Because of this, it also is usually found near the source. However, its small size and light weight can enable it to be carried on the wind to a home from a sewage plant up to a mile away! And once at a home, the fly is small enough to get in through standard screening.

The drain fly feeds on decaying organic material in mud, moss, and standing water, as well as flower nectar. It can live and breed almost anywhere that standing water or organic material accumulates for a week or more.

It is most active in the evening.

Drain Flies Are Most Likely to be Found:

  • In the home: in, on, and around sink drains, floor drains in basements and garages, unused sinks, the sides of showers, windows and walls near drains, unwashed garbage disposals, infrequently used toilets – in the bowl and/or tank, and loose tiles where moisture accumulates.
  • Outside, around the home: in or around compost piles, garbage areas, damaged septic lines, and standing water (rain barrels, tree holes, shallow polluted ponds)
  • In nature: in and around shallow, polluted water or high-moisture organic material or compost

Drain Flies Are Nuisance Pests

Drain flies cause little damage, as they do not bite and are not know to transmit disease, however, because they breed in filth, such transmission is possible.

Additionally these drain flies can become a severe nuisance pest as the eggs can be laid in masses of 10 – 200 eggs at a time, and they hatch within two days. The flies then mature within two weeks and adults live for about two weeks. So populations can grow quite large in a short time, and often seem to appear suddenly.

Find the Drain Fly Source with Traps

They key to control is finding and eliminating the source. Simple traps can be made with:

A clear plastic cup

  • Lightly coat the inside of the cup with vegetable oil or petroleum jelly.
  • Invert it over a suspected drain.
  • Leave in place for several days, but check daily.

A glueboard

  • Place glueboard upside down over a suspected drain (elevated by a cardboard frame).
  • Leave in place for several days, but check daily.

    Whatever type of trap is used, be sure to check it regularly:

    • if flies emerge they will stick to the oil or jelly and you will have found your source
    • if no flies are detected after several days, move the trap (or recoat another cup) and place it over another suspected drain or area.
    • If you cannot find a source inside the house, expand your search to outdoors.

    Get Rid of Drain Flies

    Once the source is found, you can eliminate it through removal or cleaning of the source. However, it can take persistent, ongoing work to completely eliminate a drain fly problem.

    Indoors

    • Clean in and around drains, sinks, drain pipes. Clean down into drains with a long, stiff brush.
    • Fix leaky pipes.
    • Clear any organic material, cleaning in and around all garbage containers.
    • Eliminate any other standing water or moist areas, such as wet lint in the laundry area and standing water under in drain pan beneath refrigerators or house plants.

      Outdoors

      • Eliminate standing water wherever possible.
      • Clean garbage bins, air conditioners, bird baths.

      Once you have eliminated the population, prevent future problems by keeping the area clean and clear of standing water.