Flies are not drawn to humans out of affection or curiosity, but by specific environmental cues and resources our bodies provide. These insects are driven by biological needs for sustenance, moisture, and suitable places to rest or reproduce. Their persistent buzzing and landing behavior is a natural consequence of survival instincts and highly developed sensory systems.
What Attracts Flies to Humans?
Flies possess sophisticated sensory organs that detect signals emitted by humans, guiding them towards potential resources. One primary attractant is carbon dioxide (CO2), which humans exhale. Flies have specialized receptors on their antennae that detect even small changes in CO2 concentrations, effectively using it as a beacon to locate warm-blooded hosts. This explains why they often hover near faces, where CO2 is most concentrated.
Body heat also plays a role, as flies are cold-blooded and seek warmth to regulate their body temperature, especially on cooler days. Human sweat is a complex mixture of water, salts, and organic compounds that flies find highly appealing. They are particularly interested in the salts and moisture in sweat, which are essential for their survival. Specific volatile organic compounds (VOCs) produced by human skin, influenced by genetics, diet, and daily activities, contribute to individual attractiveness. Lingering food smells or microscopic particles on skin or clothing can also draw flies, as they are opportunistic feeders.
Why Flies Land and Interact
Once attracted, flies land on humans to fulfill immediate needs, often seeking nutrients and moisture. They feed on proteins, carbohydrates, and salts present in sweat and skin oils. Their soft, spongy mouthparts are designed to lap up these liquid secretions. They may also seek moisture directly from sweat or tears, which are valuable sources of water and salts.
Flies might also land to groom themselves, cleaning their legs and bodies. A human can serve as a temporary perch for them to rest. They explore surfaces, investigating potential food sources or suitable sites for laying eggs. If a fly encounters solid food particles on the skin, it may regurgitate digestive enzymes to liquefy the substance before consuming it, a process that can involve their feet.
Health Implications and Prevention
Flies can pose health risks due to their feeding and breeding habits in unsanitary environments. They mechanically transmit pathogens, picking up bacteria, viruses, and parasites on their legs, body hairs, and mouthparts from contaminated surfaces like feces or decaying matter. When they land on humans, food, or other surfaces, they can transfer these microorganisms, potentially causing illnesses such as food poisoning, dysentery, cholera, and typhoid fever. Over 65 different human illnesses have been associated with flies.
The constant presence and buzzing of flies can be a nuisance. To reduce fly attraction, several prevention strategies can be employed. Maintaining personal hygiene by regularly washing skin helps remove sweat, oils, and food residues. Keeping environments clean is important, including promptly cleaning up spills, managing trash, and ensuring garbage cans are covered. Using screens on windows and doors prevents flies from entering indoor spaces, and insect repellents containing active ingredients like DEET or plant-based options such as oil of lemon eucalyptus or lemongrass oil can deter them from landing on skin.