Drain Flies

HYG-2071-97

Drain flies sometimes appear suddenly and mysteriously, becoming a nuisance in both homes 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. Outdoors they mar fresh paint and plug sewage filter beds (intakes and drains), getting into the eyes, ears and nose of people in the area. Bronchial asthma can be caused by inhaling fragments and dust of dead flies. Since these flies originate in filthy conditions, there is the possibility of human health disease transmission.

Identification

Adult drain flies are tiny (1/5 to 1/6 inch long), fuzzy, dark or grayish insects with the body and wings densely covered with hairs. 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 mothlike 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 polluted, shallow water or highly moist organic solids. 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

Drain flies do not bite humans but may become a nuisance by their presence in large populations. Sometimes it takes persistent effort to eradicate an infestation in the home. Concentrate on eliminating larval breeding sites from drains in floors, sinks, wash basins, bathtubs, etc. Sometimes the source of the problem is a nearby filter plant.

Prevention

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 DF-5000 Drain Fly Eliminator, a nonacid, noncaustic bacterial product that rapidly biodegrades the organic matter.

DF 5000 Gel is a highly selective active bacteria complex (not an insecticide) available in a convenient, ready-to-use 32 ounce 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. This product is not sold for the customer market. It is sold to pest control operators, hospital, restaurant and food service personnel. For additional information, contact: J.I. Holcomb Manufacturing Company.

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.

Insecticides

Indoors, aerosol space sprays of pyrethrins or resmethrin, labeled for small flying insects, will kill adult drain flies, giving temporary control. Repeat applications will be needed to kill newly emerging drain flies until the sources of the larvae are removed. Outdoors, licensed pest control operators or applicators can use cyfluthrin, permethrin and other more residual pesticides applied to dirty garbage cans, compost piles, outside sewers, window frames, etc. Always read the pesticide label and follow directions and safety precautions.

This publication contains pesticide recommendations that are subject to change at any time. These recommendations are provided only as a guide. It is always the pesticide applicator's responsibility, by law, to read and follow all current label directions for the specific pesticide being used. Due to constantly changing labels and product registration, some of the recommendations given in this writing may no longer be legal by the time you read them. If any information in these recommendations disagrees with the label, the recommendation must be disregarded. No endorsement is intended for products mentioned, nor is criticism meant for products not mentioned. The author, The Ohio State University and Ohio State University Extension assume no liability resulting from the use of these recommendations.