Flies frequently land on humans due to specific biological needs and sensory attractions. This common interaction is a result of their drive to find sustenance, moisture, and suitable environments. Understanding these reasons clarifies why humans often become a temporary landing spot for these insects.
What Attracts Flies to Humans
Flies are drawn to humans by biological cues and environmental factors. Carbon dioxide humans exhale is a significant attractant, detected by highly sensitive receptors that guide them towards a potential host. Body heat also plays a role, as flies, being cold-blooded, are attracted to the warmth emanating from human skin, especially in exposed areas.
Moisture and salts found in human sweat, tears, and mucus are highly appealing to flies, providing essential nutrients for their survival. Sweat, for instance, contains carbohydrates, proteins, and salts that flies can consume. Specific volatile organic compounds (VOCs) released from human skin, often produced by the bacteria residing on the skin, also act as enticing aromas.
Flies are also attracted to food residue, such as crumbs or sticky substances, on skin or clothing. Dead skin cells and natural skin oils can serve as potential food sources, further drawing flies to human surfaces. These chemical and physical signals create a strong attraction for many fly species.
What Flies Do When They Land
Once a fly lands on a human, its primary action is assessing the surface for nutrients and moisture. Flies possess chemoreceptors on their feet, known as tarsi, which allow them to “taste” a surface immediately upon landing. These receptors detect sugars, salts, and other organic compounds, helping the fly determine if the spot is a viable food source.
If the fly finds something edible, it may extend its proboscis, a straw-like mouthpart, to consume liquids. For solid food, such as dried sweat or skin cells, house flies often regurgitate digestive fluid onto the surface. This fluid, containing enzymes, liquefies the solid material, allowing the fly to then suck up the resulting “broth” with its proboscis.
Flies may also land to seek moisture, especially in dry environments. They might use a human as a temporary resting spot or for grooming, rubbing their legs together to clean themselves. These behaviors are driven by the fly’s constant search for resources necessary for its metabolism and survival.
Potential Health Risks
Flies can pose potential health risks due to their feeding habits and the environments they frequent. These insects often land on decaying matter, feces, and other contaminated surfaces, picking up pathogens on their bodies, legs, and mouthparts. When a fly then lands on a human, it can mechanically transfer these bacteria, viruses, and parasites.
The act of regurgitating digestive fluids onto human skin or open wounds can also transmit pathogens, as the fluid may contain microbes from previous meals. Common diseases that flies are known to carry include salmonellosis, E. coli infections, and dysentery.
While the risk from a single fly landing is generally low for healthy individuals, flies contribute to the spread of illnesses, particularly in environments with poor sanitation. They can contaminate skin, food, or open wounds, serving as vectors for various infections. Understanding their behavior helps in minimizing exposure to these potential contaminants.