Maybe a member from the gulf coast can send an assortment of lightning welk shells for you to try out.
While they're at it, perhaps they could look at fifty
or so lightning welk shells that have been vacated by the original owners
to see whether (1) they're occupied and if so, (2) by which species of
hermit crab. Also, look at an equal number of some common dextral shell
about the same size as the welks and look for the same things.
One might get an
idea of whether the crabs can accommodate shells with a reverse twist by
whether you see the same species as often in both
shells.
The left claws of many of the Pagurus genus are
teardrop shaped which is roughly the shape of the apererature of most
shells. If the shell is dextral, then the tip of the claw would be toward
the top of the aperature and the base would be at the bottom - a
reasonably good fit if he is trying to block access by a predator. If that
same animal were to use a sinistral shell, the wide and of the claw would be at
the top of the aperture, the tip of the claw at the bottom - bad fit.
Maybe that's how their claws got lost or damaged in the first place! This
is just speculation.
Can Hermit crabs, Pagurus, "change"
the size of their claws---for example, if one should be damaged or lost, would
the other grow larger to compensate, at least until the next molt? (I
think I have heard that Fiddler crabs, Uca, do that )
I usually
have a few "Pagoos" running around the bottom of my salt-water tank, but, being
in New England, I don't have any "lefty" shells small enough for them to try
out.
I would guess that it wouldn't matter very much to them---they seem
to "make do" with whatever they can fit into.
Kay