They examine their next shells carefully, inside and out, rolling them over, lifting them, poking legs and pincers deep inside, then trying them on, sometimes several times before they finally decide. You could think of them as girls trying on a new pair of jeans in front of a mirror, turning this way and that; "Does this make me look fat?"
But they don't mind broken shells. Again, like girls in frayed and torn blue jeans.
|Hairy hermit, with her backside showing through the hole in her jeans.|
Hermit crabs fit themselves into a spiral-shaped shell. And the spiral has to turn to the right, which also reduces the number of suitable shells; some snails turn to the right, some to the left. A left-turning spiral just doesn't fit.
In this photo, the curve of the back end of the abdomen is visible, as well as a bit of one of the back legs.