Big Surprise when you look closely

[Beverly]

Just before going to bed, securely prop a glass baited with a small chunk of meaty food such as scallop at a 45 degree angle near where you think the crab lives. The smelly bait should lure the crab into the glass, but it won't be able to climb out because of the angle.

As a last resort, if you do take apart your tank to get at the rock, hot tank water isn't going to budge the crab from its rock. Get a good light and look into all the crevices of each rock. Use some kind of long, sturdy, skinny metal tool to dig into the crevices. You'd be surprised how many other crabs you'll find this way.