The sudden appearance of small flies swarming around the head is a common frustration for anyone spending time outdoors. The persistent insects hovering near the face are frequently non-biting species, such as minute eye gnats (Liohippelates spp.) or vinegar flies. Their attraction is a finely tuned biological response to the resources a warm, exhaling mammal provides. These flies seek specific compounds necessary for their survival, and the human head is a concentrated source of those substances.
Sensory Cues That Draw Gnats Near
The initial, long-range signal that attracts gnats is the plume of exhaled air. Gnats possess highly sensitive chemoreceptors capable of detecting the elevated concentration of carbon dioxide (\(text{CO}_2\)) released with every breath. This gaseous trail acts as a beacon, signaling the presence of a warm-blooded host from a distance of several yards.
As the flies navigate closer to the \(text{CO}_2\) source, they use secondary sensory cues for more precise navigation. The localized warmth and humidity emanating from the mouth, nose, and eyes become important factors. The human face is a small microclimate where moisture from breath and evaporating sweat creates a localized humid environment, which the gnats detect as a promising source of liquid. This combination of \(text{CO}_2\), heat, and moisture gradients directs the gnats to the head, where they begin their search for specific nutritional rewards.
Nutritional Rewards Found on the Face
Once the flies are in close proximity, their motivation shifts from detection to consumption, focusing on specific organic compounds on the skin’s surface. Non-biting gnats are drawn intensely to the fluids secreted from the eyes, nose, and ears. These secretions, including tears and mucus, are rich in salts, proteins, and moisture necessary for the gnats’ metabolic functions and, for females, egg production.
Tears and sweat contain dissolved salts, a highly sought-after nutrient source for these insects. The gnats use specialized, sponging mouthparts to lap up these fluids, sometimes scraping the conjunctival surface of the eye to increase the flow of secretions. Moisture is crucial, especially in dry environments, providing the water needed to prevent desiccation. These flies seek out any organic fluid, including saliva or discharge from wounds, as a liquid meal.
Practical Ways to Deter Gnats
Addressing the gnats’ attraction involves disrupting the sensory cues and eliminating the nutritional rewards they seek. Since the \(text{CO}_2\) plume acts as a primary long-range attractor, wearing a hat with a brim can physically disrupt the upward flow of exhaled air, causing the flies to congregate around the hat instead of the face. Simple movement, like walking at a brisk pace, can also break up the \(text{CO}_2\) and heat plume, making it harder for the small flies to land and linger.
Managing the moisture and organic rewards on the skin is another effective strategy. Wiping sweat away frequently reduces the available salt and moisture that attracts them. Choosing unscented personal care products, such as shampoo or hairspray, can also help, as some gnats are attracted to sweet or fruity scents. While common repellents like DEET are effective against many biting insects, picaridin or oil-based repellents may offer some localized deterrence against non-biting gnats, though they are often best used as a last resort.