Hermit crabs leaving shells

I have found about 3 little hermit bodies laying dead on the sand. I'm not sure why they left their shells but obviously it was fatal. Any thoughts on why this might happen? It also seems that it was only the blue legged hermits and my red ones are all still alive. Thanks.

 

Are you sure that you're not just seeing their molts?

 

If they are leaving their shells for real I'd say one of two things not enough larger shells in there for them to move up to. Or at the risk of starting an Uproar voltage well to be more precises currant or amperage..
Do you have the tank grounded ?

 

I don't a ground probe but its only the small blue crabs leaving shells. there aren't really any shells to move into though. i've only had these guys for a few weeks. how do i know what size shell they need? the bodies are only pencil eraser sized. i don't think its molts because i picked one up and it seemed to be a body. could my damsel be pulling them out? thanks again for all the help guys!

 

I just get the assortment shells from about any local craft store 3.00 for a load of them. Then put them in the tank and the crabs will pick the ones they like. Saves on having your snails eaten /killed for their shell and or the hermits from fighting and kiling eachother to get a better fitting larger shell.