Biting flies, such as stable flies, horse flies, and deer flies, are a nuisance in outdoor living spaces, delivering painful bites that disrupt recreational activities. They can also pose a minor health risk and cause distress to pets and livestock. Addressing a biting fly problem requires a strategic approach that targets the insects at every stage of their life cycle, from larvae to adult. Effective long-term management depends on a combination of sanitation, habitat modification, physical removal techniques, and targeted control agents, as biting flies often migrate from nearby breeding sites.
Identifying and Eliminating Breeding Sources
Controlling biting flies begins with identifying and eliminating their breeding sites. Stable flies, sometimes called biting house flies, rely on moist, decaying organic matter to complete their life cycle. Their primary breeding sites include piles of fermenting grass clippings, spilled animal feed, wet hay bales, and pet waste.
Sanitation is the most effective preventative measure against stable flies. Grass clippings should be spread thinly to dry quickly or removed entirely rather than left in deep, damp piles. Compost piles must be managed correctly to ensure internal temperatures are high enough to destroy developing larvae.
In contrast, horse flies and deer flies are semi-aquatic, with larvae developing in moist soil, mud, or shallow water near ponds, streams, or ditches. Because this habitat is often natural and difficult to eliminate, managing water sources is important. Homeowners should focus on draining any standing water and ensuring that soil around bird baths or leaky outdoor spigots remains dry. Regularly disturbing or removing dense, waterside vegetation can also reduce the suitable egg-laying substrate for these species.
Mechanical Trapping and Physical Barriers
Physical methods offer a non-chemical means of reducing the adult biting fly population. Certain biting flies, particularly horse flies and deer flies, are visually attracted to large, dark, moving objects they mistake for a host. Specialized traps, such as dark-colored ball or panel traps, capitalize on this behavior. They present a decoy coated with a non-toxic, sticky adhesive. The flies land on the dark surface and become stuck, removing them from the population.
Other physical techniques disrupt the flies’ flight and landing patterns. Biting flies are weak fliers in windy conditions, making outdoor electric fans an effective barrier on patios or decks. The consistent, directional air movement prevents them from landing on people or surfaces. General-purpose outdoor fly traps using a strong-smelling, non-pesticidal bait can be strategically placed away from gathering areas to lure and capture various adult flies. Sticky traps and UV light traps, while more effective on non-biting species, can also catch some biting flies when placed in shaded resting areas like covered porches or sheds.
Chemical and Biological Control Methods
When source reduction and physical barriers are insufficient, targeted chemical and biological controls can manage biting fly populations. Adulticides involve using residual insecticides on surfaces where adult flies frequently rest to digest their blood meal. These products are generally applied to non-food contact areas, such as fences, deck railings, and the home’s perimeter, providing a long-lasting toxic surface that kills flies upon contact. Timing is important, as treatments are most effective when applied before the peak season of fly activity.
Larvicides offer a different approach by targeting the immature stage of the fly before it develops into a biting adult. For species that breed in water, like black flies and some horse flies, products containing the naturally occurring bacterium Bacillus thuringiensis israelensis (Bti) can be applied to standing water sources that cannot be drained. Bti is highly specific, releasing toxins that kill only the larvae of flies and mosquitoes without harming fish, pets, or other wildlife. For stable flies, biological control involves releasing beneficial insects, such as parasitic wasps, which seek out and parasitize the fly pupae in manure or compost. These tiny wasps prevent the emergence of new adult flies.