The house fly and other types of “filth flies” can become nuisance pests, but also are important for their potential to harm humans and animals. House flies, for example, can spread diseases such as food poisoning and dysentery. Flies, including stable flies and mosquitoes (which are also classified as flies, or Diptera), can inflict painful bites while feeding on the blood of humans and other animals, and some species transmit disease. 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.
The order Diptera is composed of the “true flies,” and is one of the largest groups of insects. Diptera means “two wings.” True flies have only two wings (one pair), instead of four wings (two pair) found in most other types of winged insects. All flies are attracted to moist organic material upon which they lay their eggs. This habit makes filth flies valuable as scavengers, but also brings them in contact with humans. Filth flies can be divided into two groups, determined by their appearance and food preferences. Filth flies, such as the house fly, blow flies and flesh flies, are relatively small, soft-bodied insects with large eyes. They are strong fliers. Other filth flies, e.g., drain flies, fruit flies and phorid flies, are smaller with more delicate bodies and legs.
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.
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.
Another important step in fly management is to exclude them from the premises. This is done by keeping doors, windows and vents closed as much is practical, and by screening and sealing around these and other fly entry points. Automatic door closing devices and air curtains that blow air away from doorways also can be installed to supplement an integrated fly management program.
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.
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.