So, here is a weird one for you. I was out in my garden this weekend and I noticed that the dirt paths that I had raked of leaves (but still had a few leaves around) all had small piles of decaying leaves. There were lots of these piles, measuring about 3-5 inches in diameter. When I pushed the leaves aside, I found a small half-inch hole under every single pile. When I dug into the hole, the only thing I found was an earthworm, which occurred in every one. I did not see this on the paths that I had not raked that still had lots of leaves, nor in the garden beds, most of which are heavily mulched with cedar chips.
I know earthworms are major decomposers of decaying leaves and that they mix the organic matter down into the soil. But do they gather the leaves into little bunches? How the heck do they do that?
I know earthworms go out onto the surface at night, grab a leaf or two and bring them back to their hole. I have witnessed this personally in my own garden (usually pathways or nearby).
But why and how?!
The book you need to read is The Earth Moved: On the Remarkable Achievements of Earthworms by Amy Stewart (Algonquin Books, 2004). It is one of those nonfiction books that is written with attention to prose, so I could not find a quick answer, but I am sure it is in there.
Other staff have also observed this, so it is not rare. It seems to be the nightcrawlers that do it. Go out at night with a flashlight to see for yourself.