I have them as well and if I could guess I think they might be Vermetid's before they build their tubes. But that is just a wild guess. I have always had them and they cause no problem.
I have some too. Mine look like a thin peice of nylon fishing line. I had a guy from my LFS stop by for a one time visit and said they were beneficial, same family as the spaghetti worm. SO.. If they look like that... its ok!