Horse flies (family Tabanidae) are large, robust insects known for their aggressive biting behavior. Only the female seeks a blood meal, which provides the protein necessary to produce eggs. They possess mouthparts that function like tiny, sharp blades, lacerating the skin to create a pool of blood they then lap up. This feeding method results in an intensely painful bite for both humans and livestock, often causing significant localized swelling. Because the female fly often feeds on multiple hosts, these insects can mechanically transmit blood-borne pathogens, including the bacteria that cause anthrax and tularaemia.
Immediate Protection and Repellents
Protecting individuals and animals relies on chemical repellents and physical exclusion methods. For human use, topical repellents containing active ingredients like DEET (N, N-Diethyl-m-toluamide) or picaridin offer a reliable defense. These should be applied evenly to exposed skin, with efficacy generally lasting several hours before reapplication is necessary.
For livestock, products approved for direct application to the coat often feature pyrethrins or synthetic permethrin-based formulations. These insecticides work as contact killers and repellents. They should be applied according to product instructions, usually focusing on areas where flies frequently land, such as the legs and flanks. Since horse flies are attracted to large, dark, moving objects, applying a protective layer before peak activity periods is highly recommended.
Physical barriers also provide an immediate, non-chemical defense. Humans can reduce their appeal by wearing light-colored, long-sleeved clothing, as horse flies are visually drawn to dark colors. Horses and other farm animals benefit from the use of fly masks, fly sheets, and leg wraps, which physically prevent the insects from reaching the skin. Providing animals with access to shaded shelter during the hottest parts of the day can also offer relief, as horse flies prefer to fly in direct sunlight and avoid dark areas.
Specialized Trapping Systems
Targeting the adult female horse fly with specialized traps is an effective strategy for reducing the population in a localized area. These devices exploit the fly’s natural instinct to pursue a warm, dark, three-dimensional object that mimics a potential host. The H-trap system, for example, features a large, dark, inflatable ball suspended beneath a funnel-shaped hood.
The black ball absorbs solar radiation, heating up and providing the infrared signature and visual contrast that attracts the female fly. After landing and attempting unsuccessfully to obtain a blood meal, the frustrated fly instinctively flies upward, a common escape mechanism. This vertical flight guides the fly directly into the collection chamber or bin from which it cannot escape.
Other designs, such as the Epps Biting Fly trap, use transparent deflectors to guide attracted flies into a tray of soapy water. Traps are most effective when placed in open, sunny locations, allowing dark components to heat up and maximize attraction. Optimal placement is typically between the horse fly’s probable breeding habitat, like a marshy area, and the location where hosts, such as livestock, congregate. When implemented early in the season, these trapping systems can achieve a significant reduction in the localized horse fly population.
Eliminating Breeding Habitats
Long-term management depends on disrupting the horse fly life cycle by modifying their breeding grounds. Female horse flies lay egg masses on vegetation or objects that overhang moist, semi-aquatic environments. The larvae hatch and drop into damp soil or shallow water, where they develop over a long period, often feeding on small invertebrates.
These larval habitats typically include muddy edges of ponds, slow-moving streams, marshy ground, or perpetually damp spots where water collects. Improving drainage in low-lying areas around pastures and barns is a practical strategy to reduce the environment’s suitability for larval development. Ensuring that water troughs and containers do not create standing water for extended periods also limits potential breeding sites.
Proper waste management further supports habitat reduction by minimizing organic debris that retains moisture and provides larval food sources. Regularly removing manure piles, decaying vegetation, and wet hay prevents the formation of the mucky conditions preferred by horse fly larvae. Eliminating these consistently wet areas makes the environment less hospitable, lowering the number of adult flies that emerge in subsequent seasons.