Amy Lacy's The Earth Moved: On the Remarkable Achievements of Earthworms explains how so.
The Kindle Edition is only $2. It's among a bunch of low priced books for the Kindle that Glenn Reynolds points to from time to time. I've been reading this one all week, and I'm simply amazed now by earthworms. All Creatures Great and SMALL, indeed. Thank you, Lord God.
(Thank you, Charles Darwin, too.)