When I started out my first salt water tank about a year ago I saw a couple of them and didn't know what they were...thought they were kinda cute. However, they turned into a ton of them and I caught over 30 in a few weeks using a store bought trap. I've read that a few are beneficial to the tank, but not that many. I've not actually seen any since then, but I'm sure there are still one or two in there. I used plankton for bait and it worked well. Some of mine were over 3 inches long and must have hitched a ride on my live rock when I set up my tank.