You can buy a bristle worm trap at a LFS. Its usually a little green tube that is like a lobster trap, they go in, but bristles make it hard for them to reverse back out. You stick a little piece of garlic food that comes with the trap in the center and the worms run to it. They work great. Only drawback is if you have snails they try to get into the trap as well.
Funny story I think, I have only 1 bristle work in my tank, been there for many many years.. and its over 8" long now. I have never seen him kill anything, just go after the dead stuff like crabs/snails and any extra food that may be in the tank. I think it has been a really good cleaner, and since it is the only one in 5 years I have spotted in my little tank I have decided to leave him be as one of the cleanup crews. I know others will probably say its to big now and can harm things.. if and when that day comes I will trap it, but for now he is just another creature in my tank.
Now, thats not to say if I had several in my tank I wouldn't try to trap em. I definately would. I have seen in my neighbors tank how fast they can get out of control if left unchecked. We put a trap in his tank and we were catching one every 30 mins for about a week straight during the days.