Now you know
Worms fascinated Charles Darwin - with good reason. Shortly after returning from his voyage aboard the Beagle in 1837, Darwin went to the home of an uncle to recuperate. The uncle drew his nephew's attention to the fact that pieces of brick left on the ground years ago were now buried a few inches below the surface - due to the action of worms, he was sure. Darwin became convinced, too. Much later, he wrote a book about worms' role in soil formation. His claim that an acre contained 50,000 worms yielding 18 tons of worm castings per year was derided as impossible. Indeed, his figures were wildly incorrect: An acre of ground contains closer to 1 million earthworms producing up to 1,000 tons of castings annually.
Source: 'The Earth Moved,' by Amy Stewart (Algonquin, 2004)