/lit/ - Literature

I'm looking fir a short story I read as a kid in a library book, it was about an entity that lived off the ghost- or spirit-energy if the dying.
The story explained how it came ti be in some swamp and at first only took the energy of insects and such, but one day it found something like a dying dinosaur and when it took its energy its mind, power and size expanded by orders if magnitude. It soon expanded over the whole planet, then leapt the space between solar systems and engulfed other planets capable of bearing life, but after it engulfed the whole galaxy, it realized that it grew too big for its own good and even though it consumed the spirit-energy of the whole galaxy, it would soon die from needing more that which was provided.
Cananyone name the story? It's making me crazy not knowing and multiple google searches came up empty. The story is really just a few pages long, if I remember correctly.