Fly Control

The flies that infest structures may be discussed in five separate groups:  filth flies:large & small, overwintering flies, biting flies and gnats and midges. Of these groups, only types of flies in the small filth fly group will regularly be found breeding inside structures. The other types of flies breed outside and are attracted to buildings by food odors, temperature gradients in the air, and exterior lighting. These factors affect how situations involving any particular fly will be handled.

Filth Flies

The habits of filth flies favor the spread of bacteria and other disease-causing organisms. Filth flies often feed and lay eggs on garbage, manure and carrion before contaminating human foods and food preparation surfaces by landing on them. When feeding, house flies regurgitate their stomach contents onto food to liquefy it before ingesting it. They also may contaminate food and surfaces by defecating on them.

LARGE FILTH FLIES

House Fly

The common house fly is a dull gray fly, ¼-inch long with four dark stripes on the middle section (thorax) of its body. House flies typically lay eggs on animal feces and garbage. White, legless maggots (the larval stage) hatch from the eggs and grow to about ½ inch. When fully grown, maggots crawl away from their food source to undergo the pupal stage. They form a dark brown cocoon, known as a puparium, and later emerge as adult house flies that can fly one or two miles in search of suitable egg-laying sites.

Blow Flies

Blow flies are so-called because the larvae develop inside the bodies of dead animals, causing the carrion to have a bloated appearance. They also are attracted to garbage. Blow flies are about the size of house flies or slightly larger. They have been called “bottle flies” because their shiny blue and green color resemble colored glass bottles, though some species are shiny black or bronze. Large numbers of these flies indoors usually indicates the presence of a dead animal such as a mouse or bird inside the structure.

SMALL FILTH FLIES

Fruit Flies

Also known as vinegar flies, fruit flies are attracted to sweet or fermented liquids such as liquor, syrup, soda pop and vinegar, in addition to ripening/rotting fruit. Females lay eggs in and around these materials upon which their tiny larvae feed. The gnat-sized adults typically have tan-colored bodies and red eyes.

Phorid Flies

Also known as humpbacked flies because of their arched thorax, phorids are tiny, dark-colored flies. The larvae feed on a wide variety of decomposing organic (of plant or animal origin) debris. If suitable materials are present, huge populations of phorid flies can build up quickly. Sources of infestation include liquefied garbage, sewage and carrion, often hidden in places difficult to inspect and access.

Drain Flies

About 1/8-inch long, adult drain flies are slightly larger than other small filth flies. Their broad, hairy wings have given rise to another name: moth fly. They also have been called sewer flies, because they infest raw sewage. Drain fly adults are often noticed resting on bathroom walls. The larvae survive submerged in the gelatinous muck that accumulates in floor, sink and toilet drains, by extending their breathing tubes to the surface for air. To eliminate infestations, drains and traps should be cleaned with a wire brush and/or drain cleaner.

Fungus Gnats (insert pix someplace)

Fungus gnats are relatively delicate, long-legged flies that look like tiny mosquitoes. The larvae of fungus gnats live in moist places where their food, fungus, grows. Indoor infestations can be associated with pigeon droppings and with over-watered potted plants where fungi develop. When removing pigeon or bat droppings, take care to wet the area first with disinfectant to kill disease-causing organisms that can be present in the droppings.

Management of Filth Flies

The control of flies in and around structures affords a classical opportunity for an integrated pest management (IPM) program. The components of a good fly management program can be modified to fit any structure, be it food processing plant, warehouse, shop, office building, or home. A five step program should include: 1) inspection; 2) sanitation; 3) exclusion; 4) mechanical control; and 5) insecticide treatment.

Inspection

Just as sanitation is the key to successful filth fly management, inspection is the key to sanitation. To eliminate fly breeding sites, one must first locate the attracting material. Often this can only be accomplished by conducting a thorough inspection of the premises, and by knowing what to look for and where to look. First, identify the flies involved, inspect for material that attracts that species and then eliminate the material.

Sanitation

The key to managing all filth flies is sanitation. Eliminating fly breeding sites, i.e., the material to which they are attracted to and on which they lay eggs, is usually sufficient to eliminate and prevent fly infestations. Conversely, without thorough sanitation, other control methods are largely ineffective. Therefore, trash should be kept in sealed containers (in trash bags and/or cans with tight-fitting lids). Dumpsters should be kept as clean as possible, emptied regularly and kept as far away from buildings as is practical. Manure and other decaying plant and animal material should be promptly removed. Also, eliminate areas of excessive moisture.

Exclusion

Despite the best sanitation efforts, flies are highly attracted to buildings because of preferred temperatures radiating from the building. All of the doors leading to the outside should be self-closing and have screens. Screens on doors should not have tears or holes and the weather-stripping around all edges of doors should be intact and tightly sealed. All windows should also be tightly sealed and have tight-fitting screens if the windows are opened. Cracks and other openings to the exterior that could admit flies should be sealed.

Mechanical Control

In addition to fly swatting, mechanical fly control includes trapping. Sticky fly paper is one type of fly trap. Ultraviolet light traps are another, often used to supplement fly control in commercial buildings. To be effective light traps must be properly placed. This type of trap should be placed where it cannot be seen from outside the building, no more than 5 feet above the floor (where most flies fly), and away from competing light sources and food preparation areas. Bulbs should be changed at least once per year. Automatic door closing devices and air curtains that blow air away from doorways also can be installed to supplement an integrated fly management program.

Chemical Control

While the use of pesticides is usually not the best means of managing filth fly problems, sometimes chemical control can be a valuable component of an integrated fly management program. Pesticide-releasing fly strips can be placed in attics and smaller, unoccupied enclosed rooms where filth flies are a problem. Contact (non-residual) pesticides labeled for fly control can be applied as a space treatment (“fogged”) to kill adult flies. This type of control provides only temporary relief, however, and cannot be relied upon to eliminate the problem. Residual pesticides – those that remain active for some time – can be applied to outdoor surfaces where flies rest, such as the outside surfaces of barns, stables, restaurants and houses. Some pesticide bait formulations are also available for outdoor fly control, including use around dumpsters.

OVERWINTERING FLIES

Cluster Fly

Cluster flies are dark gray, medium sized and measure about 1/4 to 3/8 inch long. During most of the year, cluster flies are not a problem in structures. It is only when fall approaches that they begin to enter structures in large numbers. Cluster flies begin to seek protected overwintering sites in late August and September. As temperatures begin to drop, the adult flies will be attracted to the warm walls of the building. The walls on the south and west sides are the ones usually affected because the late summer sun shines most on these sides.

Control

The best and most effective method of controlling cluster flies in buildings is to prevent them from entering the building in the first place. This can only be done with buildings that are known to have had previous cluster fly infestations. This is because the treatments have to be made in late summer before the flies begin seeking overwintering sites. Treatment of surfaces where cluster flies land before entering the building will kill most of the flies and prevent them from entering. If clusters of flies are found on open surfaces in attics, crawlspaces, or false ceilings, the best approach would be to simply vacuum the flies from these surfaces.

BITING FLIES

Horse Flies and Deer Flies

Horse flies are generally large flies which are usually brown or black in color. The eyes of horse flies are very large and are often colorful or iridescent. Deer flies are closely related to horse flies and are generally somewhat smaller. The most common species are tan or brown in color. Horse flies and deer flies are biting flies which can and will bite people. Bites can occur on any part of the body and are very painful. Horse flies and deer flies are rarely a significant problem inside structures. These flies are most commonly found inside large commercial buildings, where overhead doors are left open to allow ventilation. Once inside a horse fly or deer fly may land on or bite a person; but it is not very common.

Control

Outdoor control is impossible because of the nature of the breeding sources and the fact these flies will generally not seek out the same surfaces on which they rest. The best control is exclusion, to prevent them from entering the building. Doors and windows need to be kept closed unless they have proper screening. Overhead doors should be fitted with  a screening device. Another exclusion method is the light traps. Light traps must be properly located to maximize their effectiveness.


GNATS AND MIDGES

Midges and gnats are common names for a large number of small, non-biting flies. Many species look like mosquitoes and may form annoying swarms or clouds in the air but they do not bite. The immature stages develop in water in pools, containers, ponds, clogged rain gutters, or in some cases, wet soil or seepage areas. Most feed on living or decaying plant matter and are an important part of aquatic food chains. Many species can survive in very stagnant or polluted water.

There are no good alternatives for control of the adults, other than some pressurized aerosol sprays containing pyrethrins. These are impractical for treating anything other than small areas. These products only kill insects that are directly hit by spray particles; there is no lasting or residual effect. More gnats will quickly enter the area after the spray has settled. The gnats rest on vegetation and in the grass during the day, so an application of a spray may reduce numbers somewhat. Long term control requires trying to eliminate breeding sites, wet areas or standing water. Often, however, this is not practical.