Thanks for that picture of one of your previously-mentioned 'land crabs', Warmtoast.
I'd been wondering just what type you had over there at Gan.
That's a Terrestrial Hermit Crab.
Here, called sand crabs, they can be bought in pet shops and are reputed to be intelligent, friendly and clean.
There's a local pub in Sydney (The Friend in Hand) that keeps a dozen or so in a large aquarium-type tank.
Every Wednesday is "Crab-Racing Night" (Great Prizes to be Won!) - and it's a real hoot!
Anyway, on the question of their intelligence, I'd turned up something that military types would identify with - the "Vacancy Chain".
As you'd probably know, hermit crabs adopt second-hand sea shells as a portable means of shelter and protection.
To save taxing my limited brain cells too much, I'll just quote a couple of excerpts from Wiki:
"As hermit crabs grow, they require larger shells. Since suitable intact gastropod shells are sometimes a limited resource, vigorous competition often occurs among crabs for shells.
Several hermit crab species, both terrestrial and marine, have been observed forming a "vacancy chain" to exchange shells.
When an individual crab finds a new empty shell, it will leave its own shell and inspect the vacant shell for size. If the shell is found to be too large, the crab then goes back to its own shell and waits by the vacant shell for anything up to eight hours."
Now, here's the interesting bit...
"As new crabs arrive, they also inspect the shell and, if it is too big, wait with the others, forming a group of up to 20 individuals,
... holding onto each other in a line from the largest to the smallest crab.
As soon as a crab arrives that is the right size for the vacant shell and claims it, leaving its old shell vacant, then all the crabs in the queue swiftly exchange shells in sequence, each one moving up to the next size."
Sounds a bit better organised than what I've experienced around the 'Quartermaster's Stores' and elsewhere.