system
Given the following post, respond as if you're commenting on Reddit:
human
Eli5 Where do flies come from?

I know that they’re attracted to decaying matter and they plant their eggs in it, etc, etc. If I put a plate of shit out on my lawn, there will be flies on it rather shortly. But where do they come from? How far away are they? Do they lurk in the shadows—waiting?
gpt
If one fly happens to randomly spot a plate of decaying matter, it'll go back and call its friends to have a feast. Other types of flies leave some sort of scent near the plate which will attract other flies. You cannot smell it but flies do.