Summary

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.

ID

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, worm like and gray, with both ends somewhat darker.

Habitat & Life Cycle

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.

Pest Control

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.

Summary

Call PermaTreat at 866-737-6287 to exterminate your cluster fly infestation.

The cluster fly is slightly larger than the common house fly. There are no distinct lines or stripes behind the head, and the abdomen has irregular light and dark gray areas.

Habitat

Adult flies of the last generation of the year become numerous during the latter days of September to mid-October. As cold weather progresses, adults seek protected places to spend the winter. In many cases, this is within walls, attics, storage rooms, and basements of houses. Screens offer no protection since these flies prefer to crawl in through small openings elsewhere around the building. For this reason they are extremely difficult to keep out of houses. Isolated houses in the country are especially prone to invasion, since they offer the only warm shelter for miles around.

Life Cycle

The female lays eggs in the soil near the burrows of earthworms. The tiny maggots that hatch from the eggs seek out earthworms to feed upon. The maggots of cluster flies have never been reared on any other food but living earthworms. When full grown, the parasitic maggot leaves the body of the host and enters the soil. There are about four generations a year.

Damage

Cluster flies are parasitic on certain earthworms.

Control

Complete control of cluster flies is almost impossible since the overwintering adults are concealed in walls, attics, etc. When possible, cover the louver to the attic with screen, and use a caulking compound to seal openings to the outside. Adults are sluggish enough in the winter to be picked up with a vacuum cleaner.
It is probably not practical to attempt to control the host of cluster flies — earthworms in the ground around the house. Earthworms are important to soil, and cluster flies would simply come from surrounding areas. Chemical control should be concentrated in the home where the adults hibernate. Adults that buzz about the house can be killed with an aerosol spray.

Prevention

Prevention of cluster fly infestations is very difficult, but certainly warrants a try. Timing is the most important factor. Applying a synthetic pyrethroid to the outside of the structure with an electric fogging machine will help treat all entry sites. Application should be made in the first two weeks of August. When using strips or spray, it may be more effective to concentrate the chemical on the sunny side of the house. These walls are warmer and generally attract more flies.