Hmm. Well, it was fun to watch them eat it, but i won't try it again because I'd rather have them be safe.
I know fish eat them (hence they were at the fish store lol) I just figured a worm was a worm, in regards to these particular kind. I think there are many kinds refered to as blood worms. It was my understanding these were actual worms, not larvae. I will look into it more!

http://en.wikipedia.org/wiki/Lumbriculus_variegatus

I'm still looking, but these act more like worms, where has you can cut them into pieces and each piece lives. They have segments, and no heads such as the larvae do. I'd rather them be safe though!