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Author Topic: Why do crabs walk sideways?  (Read 4270 times)

Offline thedoc

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Why do crabs walk sideways?
« on: 23/04/2015 11:52:21 »
Why do crabs walk sideways when most other species walk forwards? Is their an advantage of sorts?
Asked by James Bentley


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« Last Edit: 25/04/2015 11:44:49 by chris »


 

Offline alancalverd

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Neat idea, but there's a simpler explanation. Crabs can swim forwards and backwards, so no need to walk in that direction. Minimum joint flexibility gives maximum strength.
 

Offline PmbPhy

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Quote from: james Bentley
I have an idea regarding why crabs walk sideways, its because it greatly increases their chances of finding food.
There is a problem with this theory. It doesn't explain why it doesn't apply to all crabs since some crabs don't walk sideways. Creating an experiment would have to entail something which would tell us what the crab is thinking because if it's for efficiency there's no physical test which could test that it's why the crab does it. I hope that makes some sense?

I looked this up on Wikipedia which said that some crabs walk sideways because of the articulation of the legs which makes a sidelong gait more efficient but that some crabs walk forwards or backwards, including raninids, Libinia emarginata and Mictyris platycheles.

See http://en.wikipedia.org/wiki/Crab
« Last Edit: 09/10/2014 09:54:40 by PmbPhy »
 

Offline jamesbentley

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i would suggest that the ones that dont walk sideways dont bottom feed or scavenge in the same way as the ones that do
 

Offline cheryl j

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i would suggest that the ones that dont walk sideways dont bottom feed or scavenge in the same way as the ones that do

As alancalverd pointed out, less flexibility means greater strength, so your question might be answered by what they mainly eat - how they are using their appendages the break open or crush things, or if they are just manipulating softer tissue prey. Sideways motion seems less speedy, but if you yourself are encased in heavy armor, it might not matter.
 

Offline CliffordK

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Minimum joint flexibility gives maximum strength.
I have eaten a few crabs, but haven't really observed a lot of live ones. 

There may be some flexibility at the shoulder joint, but all of the other leg joints just have simple flexion/extension in a single direction.  I suppose somewhat like your knee joint.  It is likely they have evolved without the musculature and joints to have rapid forward movement.

Say, with humans, we can move to the side, but much prefer walking, running, jogging in line with our knee joints and muscles.

The question might be what evolutionary niche was filled with strong legs moving to the side.  The OP's suggestion of more sensing the ground is an interesting one. 

Another thought, obviously evolution put some effort into protection (including a thick shell).  When staring down a predator, one can turn around and run, or take evasive action.  If they can't outrun the predator, then evasive action would be much better, and a quick side-step may be the best for evasive actions.
 

Offline thedoc

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Hear the answer to this question on our show
« Reply #6 on: 23/04/2015 11:52:21 »
We discussed this question on our  show















We put James' question to Naked Scientist Ginny Smith...















[Transcript to follow]















Click to visit the show page for the podcast in which this question is answered. Alternatively, listen to the answer now or [download as MP3]
« Last Edit: 23/04/2015 11:52:21 by _system »
 

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