Enlarge / An adult male hermit crab of the species Coenobita compressus ambling along on a leisurely stroll. (credit: Mark Laidre) Hermit crabs protect their soft, curved abdomens from harm by scavenging seashells and turning them into portable homes. That poses a challenge when it comes time to mate, since a rival can steal the shell while its occupant is, shall we say, otherwise occupied.