I was told by my lfs that they are both, friend as a small worm eating detrius and foe as a nightcrawler sized menace. He informed me that they are not a issue when kept in check, and keeping their #'s in check is as simple as feeding light ly for a few days and nature will run its course. The out break occurs when a reefer is a cronic overfeeder which is well most of us. i think there are other contributions here from them, another organism stirring the sandbed can't be bad. As for euthanizing the freezer is the only way i have heard for any fish/invert. Once hypothermia sets in well its naptime. Some live and die by the shrimp in a piece of panty hose as a trap in the bed, I never got it to work. I just watch the ammount of food actually hitting the bed.