Flies land on people primarily because they are attracted to the human body as a source of food and hydration. They are drawn to the warmth of the body, the moisture from sweat, and the salts, proteins, carbohydrates, and other chemicals present on the skin. Flies also respond to carbon dioxide that humans exhale, which helps them locate people. Their sensitive taste receptors on their feet allow them to detect these nutrients when they land on skin. Additionally, some body odors are more attractive to flies than others, influenced by genetics, diet, and activities. Flies do not bite when they land; instead, they use their soft mouths to suck up sweat and skin secretions. Because flies are scavengers used to feeding on decaying organic matter like feces and rotting food, the human body offers similar nutrients, making people appealing landing spots for quick nourishment. However, their presence can also pose health risks because flies can carry bacteria on their legs from unsanitary surfaces.
To reduce flies landing on you, minimizing sweat by keeping cool, maintaining good hygiene, and avoiding strong body odors or oily skin can help. Also, keeping food covered and maintaining cleanliness in your living environment will reduce their attraction nearby.
In summary, flies land on humans because our bodies emit heat, moisture, carbon dioxide, and chemical cues that signal a source of food and hydration for them. Their landing is a feeding behavior rather than aggression or random annoyance.