How does soil stay in place?
Soil can stay in place by adding just the right amount of water to it.
worms need to stay in a cold but moisturised environment as they need water to survive(then again, who doesn't?). Soil or compost would be the best place for them as they can eat and excrete there, producing a more fertile soil. Do not leave worms without water as their skin will become too dry and they will die.