Yes they eat them in nature. However they can transmit a parasite that causes gape worm. Same with snails and sluggs. But from the articles I've read that slight chance shouldn't stop your chickens from enjoying the worms. You can do some research and make a decision for yourself weather or not it's worth the risk to you. Some say the risk is very minimal but educate yourself and then decide. I just wanted to let you know it is possible. However many chickens enjoy earth worms and never have any problems.