system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do flies like landing on humans? What are they getting out of it?
gpt
Your skin is full of salts, loose cells, moisture and other delicious things flies like to eat, even more so during warm weather. 

Look closely and you'll see the fly walking around on your skin with it's mouth-tube (forgot the name) prodding around on you. That's the fly eating off you.