For many, the persistent buzzing and landing of flies can be an irritating nuisance. There are specific biological and environmental factors that draw these insects to humans. Their behavior is driven by fundamental needs for survival, including finding food, water, and suitable resting places. Unknowingly, human bodies provide a rich combination of cues that flies are expertly adapted to detect from a distance.
The Allure of Human Scent and Breath
Flies possess highly sensitive sensory organs that detect gases and chemical compounds emitted by humans. A significant attractant is carbon dioxide (CO2), which humans exhale. Flies have specialized receptors that detect even small changes in CO2 concentrations, guiding them towards potential hosts. This CO2 plume acts as an initial beacon, signaling the presence of a warm-blooded organism.
Beyond breath, human sweat and body odor release a complex blend of volatile organic compounds (VOCs) that flies find highly appealing. These include lactic acid, ammonia, and various fatty acids. The unique bacterial interactions on human skin can also alter these scents, producing compounds that further attract flies. Additionally, the warmth radiated by the human body serves as another sensory cue, drawing flies closer once chemical signals are detected.
Seeking Essential Resources on Your Skin
Once flies are drawn in by scent and warmth, human skin offers various resources essential for their survival. Moisture, readily available from sweat, is an important attractant for thirsty flies. Areas with concentrated sweat glands, like the neck or armpits, tend to retain more moisture, making them particularly appealing landing spots.
Sweat also contains valuable nutrients such as salts and trace amounts of sugars, which flies can readily consume. Flies taste these substances with their feet, absorbing dissolved nutrients. Residual proteins and fats on the skin can also serve as food sources. The microbes naturally present on human skin further contribute to the appeal, as flies can feed on compounds produced by these bacteria and yeasts.
Visual Cues and Resting Spots
Beyond chemical and nutritional allure, visual factors also play a role in why flies land on people. Flies are attracted to certain colors and contrasts. Dark colors, including black, and contrasting patterns can draw their attention, as these may mimic sheltered areas or potential food sources. While some studies suggest blue is a strong attractant for houseflies, dark surfaces often absorb heat, creating visual cues that flies use to locate resting spots.
Although sudden movements can deter flies, a relatively still person can be perceived as a convenient perching location. Flies often seek places to rest and conserve energy. The warmth emanating from the human body also makes it a desirable surface, as flies are cold-blooded insects that rely on external heat sources to regulate their body temperature. These combined visual and thermal cues contribute to a person becoming an attractive resting spot for flies.