Flies often buzz and circle around our heads. This common, sometimes annoying, experience is not random. Their seemingly targeted behavior stems from a complex interplay of finely tuned senses and signals emanating from the human body. Our heads are, in essence, an irresistible beacon for many fly species.
The Sensory World of Flies
Flies possess highly specialized sensory capabilities that enable them to detect potential attractants from a distance. Their compound eyes, composed of thousands of individual lenses, are highly adept at perceiving movement, allowing them to track even slight shifts in their environment. This visual acuity helps them navigate and locate potential targets.
Beyond sight, flies rely heavily on their chemical senses, primarily through their antennae and specialized receptors on their bodies. These chemoreceptors are acutely sensitive to a wide range of volatile organic compounds, including those found in human emanations. Thermoreceptors, also present on their antennae and other body parts, allow flies to sense subtle changes in temperature, guiding them towards warmer sources.
What Attracts Flies to Your Head
The human head presents a unique combination of attractants that draw flies in. One significant factor is the carbon dioxide (CO2) we exhale with every breath. Flies, much like mosquitoes, possess highly sensitive receptors, such as the Gr21a and Gr63a receptors in fruit flies, that detect CO2, signaling the presence of a living organism. Our heads, being elevated and relatively unobstructed, release a concentrated plume of CO2, acting as a clear homing beacon for these insects.
Body heat also plays a role in attracting flies. Flies are cold-blooded creatures and are drawn to warmth, which helps them maintain optimal metabolic activity. The head, with its rich blood supply and often uncovered surface, radiates a detectable amount of heat, making it an appealing target for flies seeking a warmer environment. This warmth can be particularly inviting, as it resembles a cozy landing pad for them.
Moisture is another powerful attractant found abundantly on the head. Sweat, tears, and even the humidity from exhaled breath provide essential hydration and salts that flies need for survival. The face and scalp tend to sweat readily, especially in warmer conditions or during physical exertion, offering flies a convenient source of these vital nutrients. Flies primarily lap up sweat to replenish salt concentrations in their bodies, although some also consume the dilute nutrients found on skin.
The diverse array of odors emanating from the head further enhances its attractiveness. Natural body odors, skin oils, and even residual food particles around the mouth or in the hair can be highly appealing. Hair products, perfumes, and lotions with sweet or fruity scents can also mimic the fermenting odors that some flies find irresistible. These various scents signal potential food sources, water, or even suitable breeding sites, making the human head a complex and inviting sensory target.
Common Culprits: Identifying the Flies
Several types of flies are frequently observed exhibiting this head-circling behavior, each with distinct motivations. House flies (Musca domestica) are common culprits, attracted to a broad range of organic matter, including general sweat, warmth, and skin oils. They seek the proteins, carbohydrates, salts, and sugars present on human skin, often licking these up with their sponging mouthparts.
Fruit flies (Drosophila melanogaster) are another frequent visitor. These small flies are particularly drawn to fermenting odors. They also use CO2 to locate places for egg-laying.
Gnats, which encompass various small fly species, are notably drawn to moisture and salt, commonly found in sweat and tears around the eyes and face. They are also attracted to the carbon dioxide in exhaled breath and can be lured by sweet or fruity scents in shampoos and perfumes. Gnats often swarm during the evening, partially seeking warmth as temperatures drop.
Why They Linger and Buzz
Once attracted to the human head, flies often linger and circle rather than immediately landing. This behavior can be attributed to their investigative nature, as they explore the potential source of attraction to assess its suitability as a feeding or breeding site. They are constantly smelling the air and examining the high-contrast areas of the face, such as eyes, nose, and mouth.
For some male flies, the head might serve as a landmark or a “lek,” a traditional gathering place where they establish territories to attract females. The movement of air currents around a person’s head, especially when walking or moving, can also keep flies in constant motion, making it difficult for them to land directly.
The characteristic buzzing sound produced by flies is a direct byproduct of their rapid wing beats. Flies must flap their wings at incredibly high speeds, typically ranging from 200 to over 1000 beats per second, to generate enough lift for flight. These rapid movements create continuous vibrations in the air, resulting in the audible buzzing noise.