I am with the "like them" crowd because I've only seen five or six of them in my tank. I would not like more than that. You can trap them and remove them from the tank. Search for 'bristleworm trap' and there will be instructions on how to make one somewhere on the internet. You can also buy some commercial traps. They are a plastic tube with a funnel end. You bait the inside and leave the trap close to the worm's lair. They come out to feed at night and follow the scent through the funnel and can't get out again from the other direction.