DRAIN FLIES                                  

Drain flies sometimes appear suddenly and mysteriously, becoming a nuisance in homes, restaurants and sewage disposal plants. Adult flies may become so numerous indoors that they congregate at windows, darken lamp shades at night, fall into food and accumulate around showers, bathtubs, sinks and floor drains, especially in the basement.  


Adult drain flies are tiny. The antennae are long (13 segments), with each segment having a "bulbous swelling" with a whorl of long hairs. Wings, appearing too large for the body, are held roof-like over the body when at rest, giving a moth-like appearance. They are weak fliers and make irregular, hesitating flights covering only a few feet in short, jerky lines. Eggs are tiny, brown or cream-colored and are laid in irregular masses of 10 to 200. Larvae are legless, about 3/8 inch long, wormlike and gray, with both ends somewhat darker.

Life Cycle and Habits

Drain flies reproduce in areas of "standing" water. The eggs, larvae and pupae can be found in the muck, slime, or gelatinous film often accumulating on the sides of drains and overflow pipes in homes, or in sewage disposal beds, septic tanks and moist compost. They have also been found in dirty garbage containers, rain barrels and tree holes. Eggs, which can hatch in 32 to 48 hours at 70 degrees F, are laid in and on the moist media. Larvae feed on the decaying organic matter, microorganisms, algae and sediment in the media. Larvae mature in 9 to 15 days and are considered valuable organisms along with the organic film in purifying sewage water. Larvae live in the organic film, breathing through tubes and feeding on sediment, decaying vegetation, along with microscopic plants and animals in filters at sewage plants. Pupae occur in or on the surface of the breeding media and, after 20 to 40 hours, new adults emerge.

The life cycle can be completed in one to three weeks. Adults live about two weeks, with old ones dying and new ones emerging. They feed on flower nectar and polluted water. During the day, adults rest in shaded areas or on walls near plumbing fixtures and on the sides of showers and tubs. Most activity occurs during the evening when these flies are seen hovering about drains and sinks. They may breed in large numbers at sewage filter plants and then may be carried by prevailing wind to nearby homes up to a mile away. Adults are small enough to pass through ordinary window screening.

Control Measures

Eliminating larval breeding sites from drains in floors, sinks, wash basins, bathtubs, etc. Sometimes the source of the problem is a nearby filter plant. Use bio-mop and/or Drain Gel on a regular basis for this purpose. Always follow directions for use on back of container.


To detect if flies are indeed coming from a drain, one needs to cover the opening during a down time with a series of glue boards. Keep the glue boards from adhering to the floor by making a small collar for the drains. Use some heavy cardboard and form it into a circle slightly larger than the drain cover (1 inch tall). Leave in place overnight or for a few days to catch flies. Also, tap loose ceramic floor tile with a broom handle in a wet room near the drain. Lift, clean and re-cement tiles.

Often the most effective method is to clean the drain pipes and traps to eliminate the gelatinous rotting, organic matter, thereby eliminating the larval food source. This can be accomplished by using DRAIN GEL OR BIO-MOP, a nonacid, non caustic bacterial product that rapidly biodegrades the organic matter.

DRAIN GEL is a highly selective active bacteria complex (not an insecticide) available in a convenient, ready-to-use container to rapidly attack and destroy the organic matter that supports drain fly development. When applied, the gel clings to pipes and traps. Pour the product around the drain edge to coat the sides. Treat five days in a row and then monthly. It does not harm plastic, metal or glass plumbing, and will keep drain lines flowing freely. Bleach should not be used in conjunction with this product as it will kill much of the beneficial bacteria and reduce its effectiveness. It is sold to pest control operators, hospital, restaurant, and food service personnel.   

Alternative methods include cleaning pipes and traps with a good, stiff, long-handled brush. It is best to remove the drain trap and use a "snake" in clogged drains to clean the pipes of all gelatinous material. If using mechanical means, flush lines with boiling water and bleach to remove any material left behind by the cleaning process. Caustic drain cleaners may also be used, although they are not as effective as other means and must NEVER be followed with bleach since Chlorine gas can be released if the two mix in the drain line.

Clean dirty garbage containers, wet lint under the washing machine, and even standing water in containers under houseplant pots. Outside the home, inspect air conditioners, bird baths, shallow stagnant pools of water and sewage treatment facilities upwind as adult flies will travel with the wind.

Drain Gel


Also available by the case




Also available by the case

For House and Barn Flies

For House and Barn Flies

Fly Magnet Bag Trap

Decorative Disposable Bag Trap


Sm & Lg GoldStick Fly Traps

Large and Small GoldStick Traps

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