One thing I noticed is that when I last fed earthworms (and I had to cut them up which was really gross) that they had a lot of dirt in their digestive track. I read that you should leave them in some paper towel prior to feeding to get that dirt out. Probably isn't going to kill the frog but better safe than sorry I guess.

Next time I can stomach to cut a worm up I'm going to use the paper towel method.