The traps you buy at the lfs are useless against the big ones~little ones they work great. I agree with the over feeding.

You can also starve them out, which is partly what I did. Cut down on feeding your fish to every other day(which is what I did also and no it wont hurt them) do this for about 2wks. You can then start feeding everyday once a day and only the amount the fish will eat.
You will first kill off the smaller ones through starvation. The bigger of course will take more time.

Or you could just catch them and sell em to your lfs

Arrow Crabs love em too.