Flies are a common presence around humans, often perceived as a nuisance. This behavior of buzzing and landing on us is not random, but rather driven by specific biological factors related to their survival and resource acquisition. Understanding these underlying reasons can shed light on why these insects interact with us so frequently.
The Science Behind Their Attraction
Flies are equipped with highly sensitive sensory organs that enable them to detect various cues emitted by humans, drawing them into our personal space. One primary attractant is carbon dioxide. Many fly species possess specialized receptors to detect changes in CO2 concentrations, guiding them towards potential hosts. Fruit flies, for instance, use olfactory neurons on their antennae to sense CO2, which can signal food sources or crowded environments.
Beyond respiration, human bodies emit other signals that flies find appealing. Body heat is another significant attractant, sensed by specialized receptors, often in their antennae. Moisture, in the form of sweat or skin humidity, also draws flies. Our skin’s surface hosts a diverse microbiome, and the resulting body odors, including natural oils and traces of food or drink, are highly attractive to many fly species. Flies possess specialized receptors for smell on their antennae and maxillary palps, allowing them to detect these airborne chemical cues from a distance.
Why Flies Often Land on Us
Once flies are attracted to our general vicinity, landing on our skin serves several specific purposes. One common reason is simply to rest, as human surfaces provide convenient, often warm, and elevated perching spots. Landing is frequently a means for flies to “sample” our surfaces. Flies have taste receptors on their legs, feet, and mouthparts. By landing and walking on our skin, they can “taste” us directly through these receptors, identifying potential sources of moisture, salts, and organic matter present in sweat, oils, or dead skin cells.
Flies use their proboscis to absorb liquids. If they find a desirable substance on our skin, they may regurgitate digestive fluids onto it to liquefy solid material before ingesting it. This behavior is part of their feeding process. Additionally, flies may land on us to groom themselves, a cleaning ritual that keeps their sensory organs functional. Sometimes, they also seek warmth.
The Impact of Their Presence
The presence of flies around people is often perceived as an annoyance due to their buzzing and persistent landing. Beyond this irritation, flies can mechanically transfer microbes from one surface to another. As flies frequent various environments, including decaying matter, garbage, and feces, they can pick up various microorganisms on their legs, bodies, and mouthparts.
When a fly lands on a person, it can deposit these microorganisms onto the skin or any open food or surfaces. Flies can carry various types of bacteria, some potentially harmful. While mechanical transfer of microbes is possible, the risk of serious illness from casual contact in everyday settings is generally low. The main concern revolves around hygiene and the potential for flies to contaminate food or open wounds, particularly in environments with poor sanitation.