Crabs are curios fellows, they like to explore and pinch and go inside of things. Lets let them do that.
Add a curiosity called Hermitting Crab, or just Hermit Crab. I have 2 ideas for how this should be created
1. Force us to pick up crabs and craft them with a petrified seashell.
2. Drop a petrified seashell near a crab, and it will go into it on its own and become hermit crab.
Image for item can either be an actual crab in a shell, or a poor mangled mess because you tried to stuff a giant crab into a shell.