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Drain flies

Drain flies are a small moth-like insect that can be a real nuisance in large numbers. Drain flies are also known as “moth flies”, “sewage flies”, and “filter flies”. The most obvious sign of a drain fly infestation is usually a sighting of the adult flies, typically found on kitchen, bathroom, or basement walls. If left alone, an adult drain fly will live approximately two weeks.


Drain Fly

  • Colouration can be brown, grey, and/or black
  • Approximately 1.5 to 5 millimeters long
  • Broad wings that are covered with small hairs, fuzzy appearance
  • Wings are held “roof-like” when body is at rest
  • Antennae are 12 to 16 segmented; long hairs are present on each segment of the antennae

picture of a drain flies

Habitat and Behaviour

A day in the life of a drain fly

These flies are not particularly adept at flying long distances, instead they will choose to “jump” or fly short distances. If you find drain in a particular room, there’s a very good chance that the source or breeding area is nearby.

Drain flies feed on decomposing organic matter and sewage. Typical breeding sites include clogged and greasy drain pipes in kitchens and bathrooms, storm drains, moist compost, and septic tanks. Female drain flies deposit anywhere from 30 to 100 eggs on the surface of the breeding medium. The larvae and pupae thrive deep within the gelatinous film and extend breathing tubes to the surface. Drain fly eggs can mature to adults in 7 to 28 days.

Drain Fly Life Cycle

Drain flies, also known as moth flies or sewer flies, are small, hairy, moth-like insects measuring 2 to 5 millimetres long depending on the species. They are weak fliers and are often seen walking near breeding sites. Females lay 30 to 100 eggs in masses on the surface of breeding medium. Drain flies are known for laying eggs in wet organic matter such as the build up that can be found in poorly maintained drains, wet manure, sewage, and compost piles. Depending on temperature, the eggs hatch in 30 to 48 hours. The larvae, also known as maggots, are legless, 3.5 to 10 mm long, pale in the middle and darker in colour on the ends.

The larval stage of drain flies lasts up to 24 days, while the pupal stage lasts between 1 and 2 days at most. The larvae feed on bacteria, fungi, and other microorganisms that develop in the breeding medium in drains, standing water, and even sewage treatment beds. When food sources become scarce, drain fly larvae may become cannibalistic. Adult drain flies usually live up to two weeks as long as a liquid food source, such as nectar, is available. A large amount of flies in the home typically indicates a problem with poor sewage drainage or overflows, which can become a continuous breeding ground. If you notice a large population of drain flies, contact a pest control professional to handle the infestation.


Why should I be concerned?

Surprisingly, drain flies are not known to transmit any diseases to humans. However, an untreated infestation will eventually lead to hundreds of flies that can make residents and visitors uncomfortable. Flies of any kind will leave a poor impression on the professionalism of businesses and their ability to maintain the establishment.

While many DIY sites will tell you that pouring boiling hot water or bleach is an effective remedy, those methods will not solve the problem. These flies deposit their eggs in the organic matter stuck to the inner walls of sewage and drain pipes. Without the removal of clogs and appropriate cleaning of the pipes, adult flies will repopulate in the very same drain. Orkin Canada’s technicians will identify the source of the problem and may use natural enzymes (not insecticides) to break down the organic matter and eliminate the breeding grounds for these flies.

Do Drain Flies Bite?

Drain flies, also known as moth flies and sewer flies, do not bite humans. Compared to other fly species in Canada, drain flies are relatively harmless.

While drain flies are not considered as threats for disease transmission, they are known bronchial asthma in susceptible individuals. The maggots (larvae) of some drain fly species can cause myiasis, a parasitic infestation.

Although their breeding behaviour makes them potential carriers of disease causing pathogens, drain flies are not known to transmit such pathogens to humans. Large infestations of drain flies are unsightly and often prove to be difficult to eradicate without professional assistance.

Tips for prevention and control

These tips may help you keep drain flies out of your home:

  • Ensure that all potential breeding sites are inspected and cleaned to eliminate and gelatinous rotting:
    • Toilets when not in use
    • Sinks in kitchens and bathrooms
    • Bathtub and shower drains
    • Floor drains in basements
  • Repair broken or loose ceramic floor tiles
  • Inspect the exterious to eliminate standing water and mold from condensation and rainwater

Get Rid of Drain Flies

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