HCA: Hermit Crab Association

I had two crabs. When I got home I looked into their tank and I see some of oNE of the Bodies laying around and then the other crab is sitting right next to the shell he was in and will not leleave the shells side why is that why did he kill him. The crab that ate the other one was always the nicest of the two and we'll I don't see how that is being very nice. Now all of the sudden this crab is very active and is half out of his shell most of the time now. Can anyone help me on what just happend

Cannibalistic aggression like this can be caused by poor diet/nutrition, inadequate shells and oncoming molt.Hermitcrabs will try to remedy nutritional deficiencies on their own even if it means eating a tank mate which is unfortunate.Hermitcrabs who are pre-molt meaning they are just a few days away from the act put off a smell like Iodine its a very clean but pungent odor that drives other hermitcrabs wild and will cause a normally docile hermitcrab to turn it on its tank mates.