Hermit Crab Moving Company

We used to have a lab technician that was a danger to everyone and everything when carrying anything that protruded beyond her body. She simply didn’t have the capacity to adjust to her surroundings when her ‘body’ changed.

Not surprisingly, she was also a terrible when it came to backing up in a car and even worse at parking. She wasn’t able to include the car as an extension of her body. Strangely she was a wizard when it came to working a micromanipulator.

I had a dog like that. He would pick up a stick and no matter what end up bumping into things, people and my other dogs. And I had a hound/shep mutt who could navigate through obstacles with uncanny ease no matter what he was carrying. He was a virtuoso.

Crabs can do this.

A crab with a plate. Scale bar, 10 mm.
Biol. Lett. 23 August 2012 vol. 8 no. 4 495-497

Hermit crabs perceive the extent of their virtual bodies

Kohei Sonoda1,Akira Asakura2,Mai Minoura1,Robert W. Elwood3 and
Yukio-P. Gunji1,
*Author Affiliations
1Department of Earth and Planetary Sciences, Kobe University, Rokkodai-cho 1-1, Nada, Kobe 657-8501, Japan

2Department of Biology, Kobe University, Rokkodai-cho 1-1, Nada, Kobe 657-8501, Japan

3School of Biological Sciences, Queen’s University Belfast, Belfast BT7 1NN, Northern Ireland, UK
*Author for correspondence (yukio@kobe-u.ac.jp).

Abstract

A flexible body image is required by animals if they are to adapt to body changes and move effectively within a structurally complex environment. Here, we show that terrestrial hermit crabs, Coenobita rugosus, which frequently change shells, can modify walking behaviour, dependent on the shape of the shell. Hermit crabs walked along a corridor that had alternating left and right corners; if it was narrow at the corner, crabs rotated their bodies to avoid the wall, indicating an awareness of environmental obstacles. This rotation increased when a plastic plate was attached to the shell. We suggest that the shell, when extended by the plate, becomes assimilated to the hermit crab’s own body. While there are cases of a tool being assimilated with the body, our result is the first example of the habitat where an animal lives and/or carries being part of a virtual body.

Guide dogs also have to perform a similar adjustment to avoid running their handlers into obstacles. They may have to adjust their virtual body up to 4X higher than their natural height. It is a remarkable achievement when you consider that unlike other animals (e.g. primates, beavers, birds) dogs don’t extensively manipulate their environment in the manner a nest building bird or a termite hunting primate.

Next time you are having difficulty getting that sofa around a corner, think about the hermit crab.

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