This is how I have caught bristle worms in the past.
First, do not feed for 3 days. You want the worms to be hungry enough to be willing to leave the safety of their holes to get to the food inside the trap.
To build the trap, I start with a small storage container with a lid. (Dollar store reusable snank cups) then cut 1.5" sits in an X-pattern around the perimeter of the container. (Like the hole in the lid of a drink cup in which you would push a drink straw through.) You want to stagger the holes and place them about 2" apart.
Then press the center of the X inward to create a small opening large enough for a bristle worm to enter but nothing else. (If you have snails they will want to get to the food also.)
Inside the container, place a piece of raw seafood loosely wrapped in aquarium filter floss or fiber fill used in quilting. Place rubble in the container for weight to hold the trap to the bottom and place in tank.
The bristle worms will crawl through the X-pattern slits and towards the food. When they crawl into the filter floss they get entangled and cannot get free.
I used this method on many tanks belonging to me and others and have gotten great results.
On 1 tank I caught over 50 in 1 night.
To harvest, simply remove the floss and toss in the trash.
HIH,
Tom G