Flies often land on humans, an experience that can be irritating. Their attraction stems from a combination of chemical and physical factors that make our bodies appealing to them.
Chemical Signals That Draw Them In
Flies possess a highly developed sense of smell, detecting chemical compounds emitted by the human body from a distance. A primary attractant is carbon dioxide (CO2), which humans exhale with every breath. Flies use CO2 as a cue to locate potential food sources, with some species being able to detect it from several meters away.
Beyond CO2, flies are drawn to volatile organic compounds (VOCs) that constitute human body odor. These VOCs are produced by bacteria residing on our skin.
Components found in human sweat also act as attractants, including salts, amino acids, lactic acid, and ammonia. All of these provide essential nutrients and moisture for flies. Flies have specialized receptors on their antennae that are sensitive to these specific odors, guiding them directly toward their source.
Physical Attractions and Comfort
Aside from chemical signals, certain physical attributes of the human body also play a role in attracting flies. Body heat provides a warm resting place, particularly in cooler environments, creating a comfortable microclimate that flies seek out.
The presence of moisture on human skin, such as from sweat, is another significant draw. Flies require water for survival and view this moisture as an accessible resource.
Visual cues also contribute to a fly’s decision to approach and land on a human. A large, stationary object like a human body can serve as a suitable landing platform. Flies are known to use visual information for landing, and this combination of warmth, moisture, and visual presence creates an inviting target for these insects.
What Happens When They Land
Once a fly lands on a human, its behavior extends beyond mere resting. Flies often land to explore the surface for potential food or moisture. They use their legs, which are equipped with chemoreceptors, to “taste” the surface they land on. This allows them to assess if the area contains anything edible.
Flies are scavengers, and human skin can offer microscopic nutrients. They are interested in consuming things like salts, dead skin cells, and skin oils.
To consume solid substances, flies may regurgitate digestive enzymes onto the surface to liquefy the material. They then suck it up using their straw-like proboscis. This action is part of their feeding process.