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Managing the Moth Fly


Managing the Moth Fly
Joseph Berger, Bugwood.org

Moth flies (Psychoda sp.) are a common small fly generally seen buzzing around drains - thus its common name of drain fly. Though it causes no real damage, its high numbers can cause it to become a nuisance pest in or around the home.


The drain fly can be identified by:

  • 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.


Because it is a poor flyer, able to fly only a few feet at a time, it is identifiable by its habit off making short, hopping flights when disturbed, rather than flying a distance. This also means that the moth fly is usually found near the source, although because of its size and light weight, it can be carried on the wind to a home from a sewage plant up to a mile away. Once there, the fly is small enough to get in through standard screening.

The moth fly feeds on decaying organic material in mud, moss, and polluted 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. During the day, the fly will generally rest in shaded spots outside or, inside, on sides of showers and unused sinks


  • In the home: sink drains, floor drains in basements and garages, in and around unused sinks, windows, walls near drains, unwashed garbage disposals, infrequently used toilets – in the bowl and/or tank, loose tiles where moisture accumulates.

  • Outside, around the home: compost piles, dirty garbage areas, damaged septic lines, standing water (rain barrels, tree holes, shallow polluted ponds), or even a nearby sewage plant,

  • In nature – shallow, polluted water or high-moisture organic material or comp


Moth flies cause little damage, they:

  • do not bite.

  • are not know to transmit disease, however, because they breed in filth, such transmission is possible.

But they:

  • can become a severe nuisance pest as the eggs can be laid in masses of 10 – 200 eggs 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 period, and often seem to appear suddenly.


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

A clear plastic cup

  1. Lightly coat the inside of the cup with vegetable oil or petroleum jelly.
  2. Invert it over a suspected drain.

  3. Leave in place for several days, but check daily.

A glueboard

  1. Place glueboard upside down over a suspected drain (elevated by a cardboard frame.)

  2. 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 over another suspected drain or area.

  • If you cannot find a source inside the house, expand your search to outdoors.

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.


  • Clean in and around drains, sinks, drain pipes. Clean down into drains with 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.


  • 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.

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