I just listened to this one.
I found myself chuckling to myself at the end: I found the whole concept really stupid.
Consider: the entirety of the tension in this story is based upon the fact that the reader (listener?) does not know the source of the blood. Thus, the ending revelation carries upon it the entire burden of breaking the tension and leaving us in awe. I really felt this one fell utterly flat.
The worms (or whatever) fed upon violence. Specifically, human violence. They urged it on, they encouraged it etc. This is to imply 2 things:
(1) Humans are somehow special. Violence on colossal scale occurs every single second of every single day in every single place amongst every single organism. Even in your own body, as you read this, untold legions of microscopic organisms wage wars of mind-boggling scale. Humans are just organisms like anything else - why should their violence be unique?
(2) Human violence is unnatural. The worms, it seems to imply, provided the impetus for slaughters untold. This is to somehow imply that the human organism is not violent by nature, but is compelled somehow from the outside. This is a deistic, moralistic point of view that is incompatable with Nature. To assume humans are peaceful by nature, unlike other organisms, and only some bizarre deity with an unexplainable interest in our insignificant existence can compel us to be violent is so ignorant of the Natural World that it made me laugh. All organisms fight. All organisms compete. Observe the brutality in gorillas or other of our closest relatives if you don't believe me.
Anyway, the horror of Lovecraft was that the universe was a vast, uncaring place where your greatest hopes and dreams were less than dust in the grand scheme of eternity. This story validated them, made them look valuable. The worms were essentially Satan - the evil entity that provokes evil in mankind, that cares about the actions of every soul. That's stupid - but almost funny.