Barn environments frequently host fly populations, which can significantly impact livestock health and welfare. The most common species include the House fly (Musca domestica), the Stable fly (Stomoxys calcitrans), and the Face fly (Musca autumnalis). Flies are vectors for numerous pathogens, carrying over 65 disease organisms, including bacteria that cause mastitis and pinkeye. Fly activity causes stress behaviors like foot-stomping and bunching, which reduce feed intake, decrease weight gain, and lower milk production. Effective fly control is necessary for maintaining a productive and low-stress barn environment.
Eliminating the Breeding Ground
The most effective long-term strategy for managing fly populations involves eliminating the organic matter where they reproduce. House flies lay eggs in moist organic material (40% to 70% moisture), such as fresh manure, spilled feed, and decaying bedding. Stable flies, which are blood feeders, develop in wet straw, decaying hay, and spilled feed mixed with urine or water, not fresh manure.
Barn management must center on the rapid removal of these larval habitats, requiring daily removal of manure and soiled bedding from stalls. This material should not simply be piled near the barn, as a single female house fly can produce 150 to 200 eggs in her 10-to-30-day lifespan. The best practice is to move the manure to a dedicated composting area located far from the barn structure.
Proper composting is a form of heat treatment, as the internal temperatures of a well-maintained pile can reach levels that kill fly eggs and larvae. If composting is not feasible, manure should be spread thinly on non-grazing fields to allow it to dry quickly, making it unsuitable for larval development. Prevention also involves strict moisture control, including repairing leaky waterers, improving drainage, and promptly cleaning up spilled feed and hay.
Physical and Mechanical Controls
Physical methods focus on blocking fly access and capturing adult flies without introducing chemicals. Strategic placement of physical barriers, such as screening on windows, doors, and vents, prevents flies from entering feed storage areas and tack rooms. This barrier keeps flies away from sensitive areas where they might contaminate feed or equipment.
Inside the barn, high-velocity fans disrupt the flight patterns of adult flies. Flies struggle to fly against air currents, so fans directing a downward and outward airflow deter flies from resting or entering stalls. This method also helps dry out potential breeding sites, supporting sanitation efforts.
Various traps monitor and reduce the adult fly population. Sticky fly tapes and ribbons capture flies, but their primary use is to gauge the size of the fly population. Jug traps use bait to lure house flies into a container and should be placed outside the barn to avoid attracting flies toward the facility.
Chemical and Biological Treatment Strategies
Active treatment strategies manage adult fly populations that have bypassed environmental controls. Chemical methods include applying residual insecticides to surfaces where flies rest, such as walls, ceilings, and support beams, killing them upon contact. These treatments offer a longer-lasting effect, but rotating the class of insecticide used each season is necessary to prevent the development of chemical resistance.
Space sprays, fogs, and mists provide a quick knockdown of flying insects in enclosed spaces, but they offer little residual effect. These applications typically contain pyrethrins and require frequent re-treatment to maintain control. Insecticidal baits, containing a fly attractant and a fast-acting poison, are effective against house flies but must be kept inaccessible to animals due to toxicity.
Biological treatment involves releasing parasitic wasps, also known as fly parasites. These beneficial, non-stinging insects target the fly pupae—the immobile, cocoon-like stage—in manure and other breeding materials. The female wasp lays her egg inside the fly pupa, killing the developing fly and ensuring a new parasitic wasp emerges, supplementing sanitation efforts.