I had an arrow crab for 2 years. In all that time I saw it catch and eat one bristle worm!!!
The pantyhose (or tights as we say over here!!!) trick, is to place some food inside it and then lie it at the bottom of the tank. The worms will crawl over it to get to the food but their bristles get caught in the Pantyhose. I caught quite a few that way in my beginner days:grinyes: