system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: why does a common house fly insist on repeatedly landing on a person despite having an entire property to fly around in?
gpt
To lick off your sweat. At least some species anyway. Human sweat is full of salt and protein (more so than other animals because of our high salt intake). Basically they're using you as a salt lick.