what can I do to catch the pest?

Question
Hello, I wrote you a while back with a probably regarding my fish being eaten.  I have tried to find the culprit, and have only seen a smaller black crab once...but it happened again, and now he/or something else has eaten my full grown copperband butterfly.  I have taken every piece of live rock out and used a close hanger to try and poke him out of every hole he might be in, but have had no luck.  I thought I might have killed him but obviously not.  I have also stayed up with the lights off searching and have not seen anything but the one crab which I was not able to get out.  I guess my question is what can I do because it is killing off my whole aquarium (it has eaten blue streak goby, pepp shrimp, blue starfish, copperband butterfly which was full grown).  And is it possible for a black crab to do this much damage and maybe to live in the sand and not in the live rock?

Thanks,
Nathan

Answer
Hi Nathan. It is totally possible for a larger crab to decimate the inhabitants of an aquarium. Are you are sure it is a crab that you have and not a mantis shrimp? The only reason I ask is because while crabs will eventually obtain a size where it can actually take down a full grown copperband butterfly mantis shrimps don't need the size because they have the speed and the strength. Most crabs that hitch hike into your tank in live rock are not reef safe because they will eat most anything that does not move but it is not likely that one that is small enough that you have trouble even finding it can cause as much damage as you have described. You may want to try to find a fish trap or a mantis shrimp trap to try to trap whatever it is that is destroying the livestock in your tank. These traps are designed to  capture the shrimp but will capture crabs and any other undesirable predator that may be living in your tank. below is a link to website that sells a trap like this. There are many different brands and you don't have to get this one but it will give you the basic construction and effectiveness of it. If your handy you may be able to make one but I have found that the commercially sold traps are much easier to deal with. This and a little patience should capture your destructive little critter before it can do much more damage!

http://www.aquariumguys.com/xterminator-mantis-shrimp-trap.html?productid=xtermi...

Good luck!