Flies are common visitors around humans. Their persistent presence is not random, stemming from specific biological needs and highly developed sensory systems. Flies detect and respond to various cues from the human body and its immediate environment. Understanding these attractants reveals how flies interact with their surroundings, driven by their search for sustenance, hydration, and suitable breeding grounds.
Chemical and Olfactory Attractants
Flies primarily locate humans through an acute sense of smell, detecting volatile organic compounds (VOCs) released from our bodies. Body odor, a significant attractant, is not solely “human” but largely a result of bacteria on the skin breaking down secretions. These microbial processes produce a complex scent profile that flies find appealing.
Sweat byproducts also act as potent chemical signals. Specific compounds such as lactic acid, ammonia, and various carboxylic acids in sweat draw flies in. For instance, lactic acid, a compound produced during physical exertion, is a major attractant for certain fly species.
Another key long-range attractant is carbon dioxide (CO2), exhaled during breathing. Flies possess specialized receptors on their antennae to detect CO2, enabling them to pinpoint potential hosts from a distance. Microscopic food particles or dead skin cells shed by humans can also serve as a food source, attracting flies seeking sustenance.
Visual and Thermal Cues
Flies also rely on visual perception and temperature sensing to find humans. Their large, compound eyes are highly sensitive to movement, which signals the presence of a potential host or a meal. Contrasting colors, such as dark clothing against a lighter background, can make humans more noticeable to flies.
Body heat provides another important cue, particularly at closer ranges. Flies possess internal thermosensors that help them detect warmth emitted by warm-blooded creatures. This ability allows them to home in on a heat source, aiding in the final approach to a human.
Open wounds or certain skin conditions can also visually attract some fly species. Wounds offer a moist, warm environment rich in nutrients like blood and tissue fluids, which are ideal for feeding and egg-laying for certain fly larvae. The odors of decaying tissue associated with wounds further enhance this attraction for species like blowflies.
Moisture and Mineral Appeal
The need for hydration and essential minerals also draws flies to human skin. Sweat provides a readily available water source, crucial for flies to maintain their fluid balance, especially in dry environments. Flies can quickly lap up moisture using their sponging mouthparts.
Beyond hydration, the composition of sweat offers vital nutrients. Salts, particularly sodium chloride, and other minerals present in sweat are essential for various physiological processes in flies. Trace amounts of sugars and amino acids in sweat can also provide flies with quick energy and building blocks for growth. Certain species, like face flies, are particularly drawn to these components on human skin.