Drain Flies

The Drain Fly

Drain flies are commonly found in humid and tropical regions, but the 2600 species of these flies are scattered all across the world. They are harmless pests that can be a nuisance nonetheless by infesting plumbing and sewage systems. Due to their moth-like appearance, they are also known as moth flies. They are small true flies belonging to the order Diptera.


Drain flies are easy to identify because of their unique appearance. Unlike house flies, blowflies or fruit flies, these flies are furry and have widely set apart flattened wings.

  • Can be 1.5mm to 5mm long
  • Dense coat of small hairs all over the body
  • Flattened wings that are not closely connected at the centre
  • Ovoid wings
  • Six Legs
  • Rainbow-like sheen on wings at times
  • Furry, segmented antennae
  • Wings are covered with scales
  • Their larvae resemble wiggling, white worms

Appearance, Behavior, Signs

Drain Fly

Drain Fly. By gbohne from Berlin, Germany – tropical moth fly (Diptera: Psychodidae) – indet., CC BY-SA 2.0, 

Drain flies look like miniature versions of moths and are attracted to damp areas. Washbasins, washrooms, kitchens, plumbing units, and drainages are all areas where they frequently breed and thrive. These furry brown flies mate and lay eggs in stagnant water. They infest areas in large numbers, and so can be a nuisance. The decomposing organic material is what allows the flies to lay eggs that can hatch and start a new generation of flies. They usually breed outdoors in the summer.

Drain flies themselves feed on organic matter – decomposed or otherwise. Moisture is what is ideal for the drain flies. However, larvae of drain flies can survive drastic temperature and oxygen level changes. They breed at a rapid pace – in just two weeks you can have a full-blown infestation. They are not known to be carriers of any diseases. The drain fly can fly fast and are often hard to swat with a hand. Drain flies will also settle on other things, such as food (and this can lead to contamination).

Signs of these flies include spotting them resting on walls, pipes or inside washbasins. Bathroom walls are a favorite resting area for these flies. They are frequently found near rotting logs, compost pits and stagnant water bodies as well.


Most homes have a few drain flies at any given point of time. But you can have an intense drain fly infestation if the excess dampness of the house is not dealt with. Leaky pipes, constantly wet washrooms, and unused buckets full of used water….these are the kind of situations that attract drain flies. Even damp walls drain alongside the house and dense vegetation (that has stagnant puddles) can make your house susceptible to drain fly invasion. Moisture is what they seek – so if your house provides it they will choose to enter it.

Kitchens, washrooms, damp basement, house sewage lines, water tanks – these are the common places that attract drain flies. Even window sills that are full of rainwater can attract them, and so can the drain pans of refrigerators. These flies can make their way through the smallest of spaces – such as cracks in walls and tears in window nets.


Drain flies are a nuisance and an eyesore. On being swatted they turn into lumpy dust. There are much better ways of eliminating them –

  • Set a vinegar trap for the drain flies near the area they are infesting. Fill a bottle with apple cider vinegar, cover with a plastic wrap that has holes in it. The drain flies will fly right inside.
  • Pour bleach down the drains to remove organic filth and eliminate the flies.
  • Keep your house clean. Do not leave any floors or walls wet for long periods of time.
  • Regularly clean the pipes, sewage and plumbing systems.
  • Fix any cracks, damaged pipes and openings in the house.
  • In case of an excessive amount of drain flies creating a nuisance in your house, seek the help of a professional local exterminator.

Drain Fly Facts

  • The drain fly is found in every state of the US
  • These flies make short hopping movements when disturbed
  • In rare cases, they have been known to trigger asthma in people
  • They are clumsy fliers

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