Last week we (or rather I) bought hermit crab #4....it came home with us an a little shell painted with a cute flower....then over the weekend we gave them a bath (never a dull moment around here) and within 24 hours it had moved into the American-flag-painted shell, that crab had moved into a previously unoccupied shell, and the green medium-sized one had evicted the large one from its gray shell and forced it to move into a shell WAY too small, but without taking over the gray shell. Also the large crab lost its antennae and a leg. we have nursed it back into its original shell and are watching it carefully to see whether or not it will survive. So you see they trade around freely, and you could decorate the shells, but if you have crabs of about the same size and temperament, they could trade and you would be calling them by the wrong name (not that they come when you call them but you get the idea). Absent some way of decorating the crabs themselves, we have un-named them and now just call them by the description of their shell and their size.