i dont know if i just got lucky with a few i had, but i boiled some water, threw the rock in and bam, dead bristle worms. i know that might not be feasible on a larger rock and im sure but it kills everything else, but if you get a really big one and your worried it might be worth a try. i had a couple that were about 2-3 inches that was biting my clam mantle and it worked for me, but the rock was only about 4x6x6 inches. when they die like that the bristle fall off and they turn a nice dark tan color!
mmmmmm