I had a Hermit Crab in 2nd grade. He was getting a bit too big for his shell, so Mom took me to to the pet shop and we got larger shell. We got home and I put it in the tank, then waited. And waited. And waited. He wouldn't take to the new shell for weeks as I remember. Finally, he shed his old shell, but he didn't get into the new one. If anyone hasn't ever seen the back end of a hermit crab, it's not a pretty sight. For days, weeks it felt like, he remained out of his shell until he died. Maybe his new shell was too big. Maybe he didn't want to live a life in captivity with no genuine hermit crab autonomy.