No, it's not she'll stealing. The aggressor hermit has a shell twice as big as the victim. That victim shell is no where near big enough. Plus there are plenty of shells lying around. I always add to the assortment, because I think it's fun when they change rides. I swear there are some individual hermits that prefer gaudy shells. I swear! But anyway, when they attack for shells, don't they always go for bigger? Plus both times they were locked together right beside a shell that would be a good fit for the aggressor.
I should have tried to get a movie of it. But the aggressor holds the victim so that the opening of their shells face each other. The victim was pulled back deeply into his/ her shell. The aggressor was flapping his face fuzz, what ever those hairs are on his face, he was flapping them like mad, and staring into the victims shell. Then sometimes reaching in and kind of poking. It might have been erotic.....or just really creepy. Can't decide.