The last time I rented a car was an intensely frustrating experience. I’d requested a subcompact to closely match the tiny Honda I normally drive, but the rental company gave me an enormous boat of a car instead. Trundling along busy roads that first day was terrifying – I repeatedly misjudged how close I was to other cars, my reaction times were off, and the hood was so wide that parallel parking became a nightmare. But by the second day of my trip I’d become accustomed to the car’s heavier carriage and slower braking, and learned how far it extended around me – which made me far less of a danger to my fellow drivers.
Turns out hermit crabs have a similar problem. A hermit crab doesn't have a heavy shell of its own – instead, it lives inside an old snail shell and carries it about on its back for protection, deftly using its tail to swing the shell around obstacles as it walks. But a crab will eventually outgrow its shell and have to find a larger one to move into.
A crab in a new shell is a lot like a novice driver in a new car -- it has to get used to the shell’s weight and balance and form a mental picture of its new shape in space before it can walk without smacking into things. And according to a recent study led by Kohe Sonoda, crabs can adapt to their new body shape quickly – when the researchers glued plastic plates to the shells used by a group of terrestrial hermit crabs (Coenobita rugosus), the crabs were able to walk normally within 10 minutes, and successfully change how they rotated their shells to get through a raceway of corners without collisions.
Relevant Paper (and image source): Sonoda. K., A. Asakura, M. Minoura, R. W. Elwood and Y.-P. Gunji, 2012. Hermit crabs perceive the extent of their virtual bodies. Biol. Lett. doi:10.1098/rsbl.2012.0085