I agree with Viper_930. I had the same confusion after reading an introductory fish book. However, at least 99% of the species are completely beneficial. Essentially every tank with live rock in it also has bristleworms. They make a good clean up crew. Just try not to pick them up with bare hands. They can sting you.
If you insist, besides the traps, six-line wrasse will eat some of the little ones. Arrow crabs will also eat some.