[kathainbowen]

Thinking about it, it's not the mantis shrimp's usual rap to "rip" or "tear" invertebrates from their shells. In truth, stomapods usually smash the shell to get the meat out, kind of like how we eat walnuts. Perhaps it's a hitchhiking crab?

At any rate, why not try a bottle trap instead of staking out (you'll just end up tired, and Murphy's Law dictates that you won't anything that night while something will end up dying the next!)? Just get a really tall, smooth glass bottle and place it beside the rock pile. Put a bit of krill or other food at the bottom and let sit. Try this for a couple of nights to see if anything turns up. If it's a crab, he'll climb in and get stuck at the base (so long as you only put food in the bottle and so long as the bottle is tall and smooth enough that it can't climb out). If it's a stomapod, most likely you'll find the shrimp at the base of the bottle.... or you'll find the bottle smashed if something startles the shrimp while it's in it.

But, if staking out is you're excuse to sit around, drink, and look at your tank all weekend as opposed to doing chores or work.... go for it!!!