These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
About the spider: If it really was another limbless spider that you saw earlier in the game, then it's not really hunger that drives the giant spider to kill every human it finds. It's revenge for its fallen brethren.
Your deaths, the deaths you inflict, and the er... "objects" surrounding you that you must use to progress. Such as ripping out a one-legged spider's leg and rolling its body into a pit of spikes to cross said pit. Or using surrounding dead bodies as flotation devices, or to trigger traps. Or the wasp later on.
Brain parasites. That is all.
That One Boss: Again, the spider. Specifically, THE one boss, since no others are found in the game.