Deer flies are persistent biting insects that can disrupt outdoor activities in many environments. Understanding what draws them to people helps minimize their nuisance. These flies use a combination of visual, scent, and thermal cues to locate their hosts.
Visual Cues
Deer flies primarily rely on vision to find hosts. They are particularly attracted to dark colors, especially blue and black; these colors absorb more heat, mimicking large animals, their common hosts. Shiny surfaces also attract deer flies, making cars or reflective gear potential targets. Movement is another strong visual attractant; as ambush predators, they pursue a blood meal upon detecting movement, with rapid movement leading to persistent pursuit. They often target the highest point of a moving object, like a person’s head or shoulders.
Scent and Thermal Signals
Beyond visual cues, deer flies detect hosts through a combination of scent and thermal signals. They are highly sensitive to carbon dioxide, the gas exhaled by warm-blooded animals, which serves as a long-range attractant, drawing them into a host’s vicinity. Once closer, they respond to human body odors, particularly compounds found in sweat. Lactic acid, ammonia, salts, and even trace sugars in sweat can attract these flies. Body heat is another significant attractant, guiding them to their targets.
Habitat and Activity Patterns
Deer flies thrive in specific environments, primarily damp, wooded, or wetland areas. These include marshes, swamps, pond edges, and stream banks, serving as breeding grounds for their larvae. They are strong fliers and can travel considerable distances from their breeding sites. Deer flies are active during daylight hours, from late spring through late summer, with peak activity in June and July. They prefer warmer temperatures (72-90°F) and are most bothersome on warm, sunny days with minimal wind.
Reducing Your Appeal
Minimizing your attractiveness to deer flies involves several strategies. Wearing light-colored clothing, especially white, can deter them, as they are less attracted to these shades than dark colors. Thick, loose-fitting long-sleeved shirts and pants provide a physical barrier against their painful bites. Since deer flies are attracted to the head and shoulders, a light-colored hat offers additional protection.
Avoiding outdoor activities during peak deer fly hours, particularly on warm, sunny days with little wind, can significantly reduce encounters. While some repellents containing picaridin or permethrin (applied to clothing) may offer benefit, DEET is generally not highly effective against deer flies. Remaining still when flies are present can also make you less noticeable to these visually oriented insects.