The persistent buzzing of flies around a person is not random annoyance but a targeted search for resources. These insects, which include house flies and bush flies, are primarily driven by the need for food, moisture, and warmth. A human body represents a temporary, moving source of all three necessities. This behavior is a direct result of their sensory systems detecting the chemical and physical signals a person emits into the surrounding air.
Chemical and Physical Attractants
Flies use sensory cues to locate a potential host, beginning with the detection of exhaled breath. Carbon dioxide (\(\text{CO}_2\)) is a powerful long-range locator, as the gas is released at a concentration far higher than the ambient atmospheric level. This plume of \(\text{CO}_2\) acts like a chemical beacon, guiding the insect toward a living organism.
As the fly gets closer, it relies on physical cues. Body heat radiating from the skin serves as a strong thermal signal, indicating a warm-blooded animal. Humidity sensors on the antennae also detect the moisture released through respiration and perspiration, which helps the fly home in on the body’s surface for closer inspection.
Why Flies Target Specific Areas
Once a fly has located a person, its attention shifts to sources of liquid nutrients and salts on the skin’s surface. Flies are unable to chew solid food, so they must find liquids to consume. Sweat residue is highly attractive because it contains a mix of water, salts, and trace organic compounds like proteins and sugars.
The human eye is a frequent target because of lacrimal secretions, or tear moisture, which provides a rich source of both water and salts. The skin is coated in a thin layer of oils and microbial fauna, which house flies readily consume. Flies use sensory organs on their feet to “taste” the surface as they walk, identifying areas with desirable compounds. They may also be drawn to minor open wounds or scratches, as the exposed interstitial fluid offers a concentrated nutritional source.
Disease Transmission Risk
The fly’s habit of feeding on diverse matter makes its contact with humans a health concern because of its role as a mechanical vector. A fly does not bite to transmit disease, but it transfers pathogens on its body. It frequently lands on decaying organic matter, garbage, and feces, where bacteria and viruses adhere to its legs, mouthparts, and body hairs.
When a contaminated fly lands on human skin, food, or mucous membranes, it can deposit these microorganisms directly onto the surface. Flies also regurgitate digestive fluids onto solid food to liquefy it before consumption, and this fluid can contain pathogens from a previous meal. Common pathogens transferred include bacteria like Escherichia coli and Salmonella, which can lead to foodborne illness.
Effective Deterrence Methods
Reducing the factors that attract flies is the most practical way to minimize contact. Since flies are motivated by moisture and organic material, environmental control is effective. This involves immediately cleaning up food spills and managing any waste that could serve as a fly breeding ground.
Personal hygiene also reduces attractants, as frequent washing decreases the accumulation of sweat, skin oils, and microbial residue on the body. Simple physical barriers prevent flies from reaching people, such as installing fine mesh screens on windows and doors. Using powerful fans to create air currents disrupts their flight patterns, making it difficult for them to land or maintain a steady approach. Essential oils like eucalyptus, peppermint, and cinnamon can also deter flies by overwhelming their olfactory receptors.