Horseflies are a common nuisance during warmer months, often appearing to relentlessly pursue humans and animals. This persistent behavior can be perplexing, but understanding their biological drivers and sensory cues reveals why they seem to “chase” targets.
The Biological Imperative for the Chase
Only female horseflies bite, driven by a biological necessity. They require a blood meal to obtain protein essential for the development of their eggs; without this high-protein intake, they cannot successfully reproduce. Male horseflies, in contrast, do not bite and primarily feed on nectar.
This need for a blood meal makes female horseflies persistent in their search for hosts. They are not particularly selective, targeting various warm-blooded animals, including humans, horses, and cattle. This behavior is a crucial survival and reproductive strategy for the species, ensuring the continuation of their life cycle.
Sensory Cues That Attract Horseflies
Horseflies employ a sophisticated array of sensory mechanisms to locate potential hosts from a distance. One primary long-range attractant is carbon dioxide (CO2), which is exhaled during breathing. The more active an individual is, the more CO2 they release, potentially drawing increased attention from these insects.
Heat also plays a significant role, as horseflies are drawn to warmth and use thermal cues to find targets. Body heat signals a potential host, and exercising or spending time in direct sunlight can make an individual a more appealing target.
Movement is another strong attractant, as horseflies are highly sensitive to moving objects. Motion makes a target more noticeable, and their excellent vision allows them to detect prey from a considerable distance. They are particularly drawn to dark, shiny surfaces, partly due to the way these surfaces reflect polarized light.
Additionally, horseflies are attracted to certain olfactory cues, including sweat and body odor. Lactic acid, a component of sweat, is a notable attractant, which explains why physically active individuals may seem to be targeted more often. Wetness on the skin, whether from sweat or other moisture, can also enhance their visual appeal by creating shiny surfaces that reflect polarized light.
Understanding the Horsefly Bite
A horsefly bite is often described as painful, a sensation typically felt immediately upon impact. This intense discomfort stems from their unique mouthparts, which are designed to cut rather than pierce the skin. Unlike mosquitoes that use a fine proboscis, female horseflies possess saw-like mandibles that slice into the skin to create an open wound.
Once the skin is cut, they use a sponge-like proboscis to lap up the pooling blood. Horseflies also inject anticoagulant saliva into the wound to prevent the blood from clotting, ensuring a continuous flow for their meal. This cutting mechanism and the absence of an anesthetic contribute to the sharp pain experienced by the host. The bite often results in a raised, discolored welt, accompanied by swelling and itching around the affected area.
Strategies to Avoid Horseflies
Minimizing exposure to horseflies involves understanding their attractants and modifying behavior. Wearing light-colored clothing can help, as horseflies are less attracted to lighter hues compared to dark colors like black or blue. Loose-fitting clothing is also advisable, as their strong mouthparts can sometimes bite through thin or tight fabrics.
Avoiding peak horsefly activity times, which often include the hottest parts of the day, can reduce the chance of encountering them. Horseflies are also less active in dark or shady areas, so seeking shelter there might offer some reprieve. Using insect repellents containing ingredients such as DEET, picaridin, or citronella can help deter them, though their effectiveness may vary compared to other insects.
Covering exposed skin with long sleeves, pants, and hats can provide a physical barrier against bites. If horseflies are present, avoiding rapid movements may also be beneficial, as they are drawn to motion. Combining these strategies can help reduce the likelihood of being chased and bitten by these persistent insects.