Bristleworms are scavengers. At the most, in my personal experience, opportunistic, but really mostly just cleaners. If something goes by the wayside they tend to take care of it before it can spoil your water.
If your sps are bleaching and you've lost two fish I'd be wondering about your water quality and possible hidden pests that could be a problem. Granted, butterflies are hit and miss and overall difficult to maintain for long periods of time in a tank, but six lines are generally pretty hardy.
I do, however, recommend you dont touch the worm. I've accidentally gotten their bristles stuck in my fingers by over turning a rock or frag where they had hidden underneath and it isnt pleasant. If you do get stuck with them rinse with vinegar right away. Reminds me of a fuzzy cactus that sticks in you but you dont want the wound to get infected so clean it very well.
Tell us a little more about your tank? water? temps? bulb age? other inhabitants? Any clicking noises? Maybe we can brainstorm what may be causing that stuff.