Flies circling around a human head is a common, often irritating, occurrence during outdoor activities. This behavior, while seemingly random, is a result of specific biological attractions and environmental cues. Understanding this phenomenon involves examining how flies detect and respond to signals emitted by the human body.
What Draws Flies to Humans Generally
Flies are equipped with specialized sensory organs that allow them to detect cues indicating potential food sources, moisture, or warmth. One significant attractant is carbon dioxide (CO2), which humans exhale. Flies can detect CO2 from a considerable distance, using it as an initial signal for a living organism. This gas acts as an invisible beacon, guiding flies towards a potential host.
Beyond CO2, the warmth radiated by the human body also serves as an attractant. Human sweat and natural skin oils further contribute to this attraction. Sweat contains various compounds such as lactic acid, ammonia, and salts, which flies can consume for moisture and nutrients. The overall body odor, a blend of volatile organic compounds produced by skin bacteria and secretions, can also draw flies seeking sustenance.
Why the Head Becomes a Focal Point
The head often becomes the primary target for circling flies due to a concentration of these attractants. The exhaled CO2 forms a more concentrated plume around the head, making it a particularly strong signal. Flies possess sensitive receptors that can detect even subtle changes in CO2 levels, guiding them directly to this emission source.
In addition, the head can be a significant source of body heat, especially when uncovered, providing a localized warm spot. For some fly species, particularly non-biting midges, the head can also serve as a “marker” for lekking behavior. Lekking involves male flies gathering in swarms around prominent objects to attract females for mating. A human head can inadvertently become a chosen landmark for these aerial mating displays. Moisture from sweat, as well as residues from hair products or skin oils, can provide additional localized attractants on the head, offering flies readily available moisture and nutrients.
Strategies to Deter Circling Flies
Minimizing attractants can help reduce the presence of circling flies. Regular showering and using unscented personal care products can decrease the appeal of sweat and body odors. Avoiding sweet or floral fragrances in perfumes, lotions, or hair products may also help, as these scents can attract flies.
Physical barriers offer a direct method of protection. Wearing hats can obscure visual cues and reduce heat emission from the head. In areas with high fly populations, a head net or a hat with an integrated net can provide an effective physical barrier, preventing flies from reaching the face and head. Insect repellents can also be applied to exposed skin or clothing. Products containing active ingredients such as DEET, picaridin, or oil of lemon eucalyptus are effective against many biting insects, including flies, by interfering with a fly’s sense of smell, making the treated person less detectable.