I generally don't kill them, but just a minute ago, I was scraping the coraline off my 8g biocube, and this foot long green bristleworm, that I have been trying to catch for the longest time was totally out in the open, so I cut it in half with the razor blade and took it out. So after I made sure it was dead by putting it in fresh water, I noticed this red kind of sharp looking thing sticking out of where I had cut it in half. So I got out some tweezers, and pull it out, and sure enough, it was like a quarter of the body of a hermit crab. Well of course this piqued my interest, and so fully disected it, and there must have been the bodies of at least three hermit crabs in this worms intestines. I can't say for sure that it had killed them, but I think from now on, when it comes to the really big ones, its definately 'kill them all'. Plus they just gross me out.