Worms create great soil. They don't deplete the soil. Their castings are known as black gold. In contrast, a 7000-acre field of corn treated with chemical fertilizers and pesticides was found to not have any worms in it at all. Worm castings are the perfect pH for plants.
Worms burrow deep and bring up trace minerals.
We need more information about worms and their role in the eco-system. A grandmother in Denmark ordered 250 worms and cut them all in half, thinking she'd get 500 worms for her garden. Actually she ended up with 250 worms. The head end eventually grows a new tail, but the tail end just stays as it is. And yes, a worm has a brain.