I know that, generally speaking, a dog or cat can ride in an airplane with no harm done. Does anyone know how other animals react to airplane rides?
More specifically, will my hermit crabs kick the seashell if I take them as a carry-on?
My WAG is that in the passenger cabin they should be ok, but I wouldn’t send them as freight. Of course, depending on where you are taking them, there may be a quarentine, if the know about them.
Remember IANAHermitCrab.
Thank you, dragonlady, for the mental image of you hunkered up in a shell with your little buggy eyes and claws slowly tapping at a keyboard. 
Many aircraft have what’s known, aptly, as a “dead-dog switch” for the cargo compartment. Unless you are confident that it will be in the “ON” position (i.e. heating is on for the cargo area), it is a Bad Idea™ to pack any living critter in your luggage. Not, of course, that anyone was suggesting that. Just a reminder, in case anyone was comtemplating ways to avoid any potential quarantines…
No one remembers the pig goes beserk on airplane story? 300lb pig went beserk on airplane - with non-hilarious results.
Find it here (or in a dozen other places)