Flies frequently land on humans. This behavior is not random; it stems from flies’ biological needs and their perception of humans as sources of sustenance and warmth.
The Science of Attraction
Flies detect cues emitted by humans. Carbon dioxide, exhaled with every breath, acts as a long-range signal, alerting flies to potential hosts. Flies are also drawn to body heat, as they are cold-blooded creatures that rely on external warmth to regulate their body temperature. The warmth radiating from human skin, especially the face, provides an appealing environment.
Human body odors further contribute to this attraction. Sweat contains compounds like lactic acid and ammonia, which flies find appealing. Skin oils and other organic compounds on the skin’s surface also serve as attractants. Even perfumes, lotions, or residual scents from soaps can inadvertently mimic attractive odors, drawing flies closer.
What They Seek on Your Skin
Once flies land on human skin, they seek specific nutrients and moisture. Sweat provides both moisture and salts, vital for a fly’s survival and neurological function. Flies also look for proteins, carbohydrates, and other chemicals present in skin secretions and dead skin cells. Their sponging mouthparts are adapted to absorb these liquids, and they may even regurgitate digestive enzymes onto the skin to liquefy solid particles.
Open wounds or cuts are particularly attractive due to the presence of blood, tissue fluids, and decaying tissue, which offer a rich source of nutrients. Tears and other eye fluids also contain salts and moisture, attracting certain types of flies, like gnats, to the area around the eyes. Residual food or drink particles on the skin can similarly act as strong lures.
Beyond Annoyance: Potential Risks
Flies can pose a minor risk due to their ability to transfer microorganisms. They frequently visit unsanitary environments such as decaying matter, feces, and garbage, where they pick up various pathogens on their bodies, legs, and mouthparts. When they land on human skin, food, or open wounds, these pathogens can be mechanically transferred.
House flies, for instance, are known to carry over 100 types of pathogens, including bacteria, viruses, fungi, and parasites. This can include bacteria linked to common illnesses such as food poisoning, dysentery, E. coli, and Salmonella. While the risk of serious infection from a single fly landing is generally low for healthy individuals, it can be a concern in environments with high fly populations or for vulnerable populations like infants, the elderly, or those with compromised immune systems. In some cases, flies laying eggs in open wounds can lead to a condition called myiasis, where larvae infest living tissue.
Simple Steps to Deter Flies
Maintaining personal hygiene, such as regular showering, helps reduce body odors, sweat, and skin oils that attract flies. Wearing light-colored clothing, particularly white, light yellow, or light blue, can also help, as flies are often less attracted to these hues compared to darker colors.
Using insect repellents containing active ingredients like DEET or picaridin can provide a barrier. Natural deterrents such as essential oils like lavender, peppermint, eucalyptus, citronella, or lemongrass can also be applied to the skin or used in the environment. Avoiding strong perfumes or lingering food odors on the body can also help reduce attraction. Keeping surroundings clean, promptly disposing of waste, and covering food are also effective measures to prevent flies from congregating near humans.