Hello Noelle. It is actually very harmfull for anything to be attached, drawn or painted on there shells because they sometimes eat there shells or the shells around them. Many large groups are trying to get them to stop ruining all those beautiful shells by painting on them. Good luck with your new batch of Crabbies and go to hermit crab association maybe that web site will be able to help you, help keep them alive for many, years to come because they live up to at least if not more then 40 years.