Drain Fly Facts & Information

Everything you need to know about drain flies

An annoying and troublesome pest to homeowners is the drain fly, also commonly known as the moth fly, filter fly, or sewage fly. Moth flies are frequently found indoors on windows, sinks, and walls. The source of the fly infestation is generally from sinks and floor drains, or from nearby sewage plants or waste disposal areas. Polluted waters and wet organic materials are preferred breeding areas of this fly.

The adult fly is about one-tenth inch long (about one-third the size of a housefly). It has a dark gray body and lighter colored wings. The body and wings are densely covered with long hairs which give the body a fuzzy or hairy appearance, which explains why they are also known as “moth flies”.

Eggs are deposited throughout the spring and summer in moist, decomposing organic materials. The gelatinous organic deposits, which tends to accumulate in drains, provide an ideal breeding site. Eggs hatch into the maggots, which feed in this organic matter. Under favorable conditions, maggots mature in about two weeks and form a hard shell (puparium) within which the pupa forms and from which the adult fly emerges. There are drain fly treatments that can be done in commercial kitchens with floor drains. They are not as prominent in homes.

Not the fly you have?

How Did I Get Drain Flies

Your drains are open and ready to build up the organic matter drain flies love. So keeping them out is difficult. If you’ve started to spot these tiny moth-like flies around your home, you may not immediately realize you have an infestation growing in your pipes. There are a few sure ways to check if more drain flies are living and breeding in your pipes. Drain flies frequently lay eggs in the organic material that builds up right at the opening of your drain. Remove the drain cover, scrape some of the slime off the sides, and look for thin, tube-like, drain-fly larvae. If you don’t spot any here but are certain you have an infestation, this could be a sign that the eggs are being laid deeper within your pipes. You can pour boiling water carefully down your drain 1-2 times a day for about a week to get rid of the drain flies that are already there. This will ensure that the flies do not return overnight if the water did not catch all of the organic material built up inside.

Problems Caused by Drain Flies

Drain flies are not known to transmit human pathogens. Even so, they live in drains and sewers so wherever they land, they are picking up bacteria. They prefer unsanitary conditions so taking care of that source can take care of the drain fly infestation. Once inside your drain, they can plug pipes and spread bacteria to food or food surfaces. They are not strong fliers but can be blown into your home or business by the wind. Keeping them out may be difficult but our bioremediation strategies can help with drain fly control in businesses with floor drains. Drain fly treatment at home is based on sanitation strategies and education. Either way, we can help.

How Do I Prevent Drain Flies

Control varies with the origin of the moth fly infestation. The most economical and sanitary way is to remove the organic material in which they breed. This requires cleaning sinks, drain pipes, and traps with a stiff wire brush or by steam. Several new products are now available that contain either bacteria or enzymes which breakdown the gelatinous scum in drains. They are applied as either a pour around the drain lip or injected as foam. Most pest management companies provide this as a service. To determine which drain is infested, place a jar over the outlet or tape a plastic bag over the opening of the overflow outlet. Check the container at intervals for adult flies.

Drain flies look for pools of sitting water containing sewage and other organic material. Preventing drain fly infestations requires clean pipes that are frequently flushed out either with water, or in more extreme cases, cleaning solutions on a regular basis. If you have a drain that frequently goes days or weeks without use, close it up with a stopper so that drain flies cannot find a home there in the meantime. In addition to pouring boiling water down the drain (carefully!), you can also try a combination of baking soda, salt, and vinegar. This go-to mixture of pantry items creates a natural cleaning solution. Pour it down your drain and let is sit overnight. The baking soda expands with the vinegar, reaching more areas than the boiling water. After letting the solution sit until the morning, flush out the pipe with boiling water.


We’re passionate about keeping flies out of your home or business because we live and work here – it’s our neighborhood, too. We’ve been keeping homes and businesses in Kentucky, Indiana, and portions of Ohio safe from pests since 1972. OPC Pest Services has the experience you can trust.
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Louisville, KY