If you have a visible population, you're probably overfeeding.
Anyway, if you want to trap them, take a small pop bottle, cut off the top and invert it back into the bottle. Secure this with some super glue.
Now throw some sand into the bottom to weigh it down and a piece of food on top of that. Bury this in your sand so that the lip is only 2" or so above the surface. Provide a small rock to act as a ramp. Leave overnight, profit.
Too bad you weren't local, because I would be all over picking up a bunch to seed into my tank
