Really weird situation going on

[kuza]

Maybe, but I assume they chew on the spiral when the sleep/relax since it's right around their mouth area that they modify it.

When they jiggle they will just be sitting out of their shell a bit, so it would have to be their stomach doing the modification if that were the case

[DragonsFly]

Somebody a while back posted that he was going to try to do his science fair project on how they modify their shells. He seemed to think they might produce some kind of chemical excretion that helped to break down the spiral. His alternate hypothesis was that they somehow grind it down with their exoskeleton. I don't think he ever found a good way to test either one of those hypotheses, though. . .

[wodesorel]

I'm going to throw out that since there is new substrate and the tank has been cleaned and new things like clean shells added, that Mr. E is establishing territory again thinking he is someplace new. Es and PPs can coexist just fine, but they're never going to be able to communicate with each other like they could with another of their own species. It could be that the PP isn't picking up on the Es more subtle communication of trying to be dominate and claim the tank, so it's starting to turn a bit physical so the message will come across. When you have a lot of crabs it's not as noticeable since they tend to calm down in larger groups since they know they have to share, but with only two they can get pretty feisty since it's just one on one.

I always recommend a bath so they smell the same when they start to get on each other cases, since in my experience it's usually enough to get them to calm down again. Otherwise just keep an eye on them to make sure it doesn't go to far.

[Craftycrabber]

I think there is a good possibility that you are right Fly.