Horse flies (family Tabanidae) are persistent insects whose presence can quickly ruin time spent outdoors. Only the females bite, requiring a blood meal to gain the protein necessary for egg production. Unlike mosquitoes, which use a fine proboscis, the horse fly possesses blade-like mouthparts that slice into the skin, resulting in an immediate and painful wound. Understanding how these insects locate a host is the first step toward successful personal defense.
What Attracts Horse Flies to People
Female horse flies employ a dual-strategy system to locate a host, relying on both chemical and visual cues over different distances. Long-range detection is primarily achieved by sensing the carbon dioxide (\(\text{CO}_2\)) exhaled by mammals during breathing. This chemical signature acts as an airborne beacon, guiding the flies toward a potential blood source from a considerable distance.
Once they are within closer proximity, visual and thermal signals become the dominant attractants. Horse flies are notably drawn to large, dark, and moving objects, which they often associate with their natural hosts, such as cattle and horses. They also sense heat and shiny surfaces, which is why they are frequently found near sunny areas or bodies of water where light reflects. The combination of movement, warmth, and dark colors makes a person an easy and appealing target.
Using Topical Repellents for Personal Protection
Applying insect repellents directly to the skin or clothing is a primary defense strategy, specifically targeting the flies’ close-range host-seeking behavior. The most effective chemical repellents are those containing DEET (N,N-Diethyl-meta-toluamide) and Picaridin. Products with a DEET concentration around 20% offer significant protection against horse flies, though effectiveness varies based on the specific formulation and environmental conditions.
Picaridin, a synthetic compound derived from the pepper plant, is an excellent alternative to DEET and often preferred because it is non-greasy and virtually odorless. Repellents containing 20% Picaridin are highly effective against biting flies and can provide a protective barrier for many hours. These chemicals work by interfering with the insect’s chemoreceptors, essentially masking the attractive odors of the host.
For those preferring non-synthetic options, essential oil-based repellents containing lemon eucalyptus oil (OLE) can offer some degree of short-term protection. While not as robust or long-lasting as DEET or Picaridin, these natural alternatives must be applied more frequently to maintain their efficacy. When using any repellent, it is important to apply a uniform layer to all exposed skin and to reapply according to the product label, especially after swimming or sweating.
Physical Barriers and Behavioral Strategies
Modifying clothing choices and personal behavior can significantly reduce your attractiveness to horse flies. Since these insects are drawn to dark colors, wearing light-colored or white clothing makes you less visually appealing as a potential host. Choosing garments made from densely woven fabrics, particularly long-sleeved shirts and long pants, creates a physical barrier that prevents the fly’s mouthparts from reaching the skin.
Behavioral adjustments involve avoiding the times and locations where horse flies are most active. Their biting activity typically peaks during the warmest part of the day, often between 11:00 AM and 4:00 PM, especially in sunny conditions. It is advisable to limit outdoor activity during this mid-day window, particularly near their preferred breeding grounds. Horse flies commonly congregate in areas near water, such as marshes, ponds, and streams, since their larvae develop in moist environments.
Minimizing rapid movement is another effective strategy, as movement is a powerful visual attractant for the flies. If a fly begins to circle, moving slowly or seeking the shade of a dense tree canopy can make you less detectable. Utilizing simple physical barriers like head nets can also provide immediate relief in heavily infested areas, protecting the head and neck where flies often target.