Here is a picture of one of the little guys. They are generically called red wigglers, though not all of them are
necessarily Eisenia fetida.
The other cool tiny critters we have seen lately are the bark lice on the crepe myrtle in the back yard. I had never noticed these before and was sure they presaged doom for my aging shade tree. A quick googling revealed they are in fact beneficial and live off the fungi on the tree. So, not really beneficial for fungi. But for the tree,
they're like an egret on a rhino's back. It is tough to see these little guys in the photo. They scrabble around in a herd and if you wave your finger at them they scatter--very slowly. I wish I had a good lens for up-close photos.