Conversing with the mind spiders proved fruitful. This is what the mind spiders propose for their existence.
The mind spiders were a mental transformation of red spiders from xkcd, it seems.
First were the red spiders, and then there were four-legged black spiders in an infinite 2d world, and then there were the mind spiders. The black spiders became mind spiders after mental exposure to a misunderstanding of antimemetics, and thinking that antimemetics was about fighting memetic beings instead of being concerned with beings who cannot be memetic.