Kind of like if, say, Centipedes cleaned your house... even though they have a beneficial job, most people are creeped out a little bit and want them gone. I had one in my tank as a hitchhiker during the cycle, but have not seen it in months. I assume it's still alive, but I check out the tank under moonlights often. He used to be easy to spot, but nothing for a long time. I think I have a tiny fireworm in my sump, though.