I agree with most people that bristle worms are a benefit to our tanks: with that said, beware that there are some that develope taste for things we want to keep. One morning last week I peered into my tank, and saw a bristle worm munching on one of my shrooms. This worm was about threee inches long, and about as big around as a pencil. He was fully exposed so I took my handy plastic tongs and grabbed him, I then took him outside and fed him to one of my many "pet" fire-ant mounds. I have many of these worms in my tank, and I still think they're a great benefit. Unless you have one that's a renegade, like the one I had, I'd really suggest that you leave them.