James Bentley asked:
Why do crabs walk sideways when most other species walk forwards? Is their an advantage of sorts?
We put James' question to Naked Scientist Ginny Smith...
Ginny - Well, the simple answer is because itís the way their knees bend. So, if you think about our knees, they bend forwards and that allows us to take step forwards whereas crabs, their legs are on the side and their knees bend outwards, so they can only move sideways. The more interesting answer is taking into account, of course, evolution. Weíve evolved to walk forwards. Most animals walk forwards because you can see where you're going better. But for crabs, there must be a reason why itís okay for them to walk sideways.
They spend a lot of their life buried under the sand and theyíve developed these kind of long, flat bodies that make it very easy for them to sort of squiggle under the sand and hide there. Having their legs on the side kind of fits in with that elongated shape. They also donít really need to walk that fast - they're scavengers. They donít chase prey very much. So actually, they donít need to be great runners and being able to hide has been more useful for them.
Chris - Does the crab nebula move sideways?
Carolin - No. well, it moves outwards in every direction very, very fast.
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. alancalverd, Thu, 2nd Oct 2014
i would suggest that the ones that dont walk sideways dont bottom feed or scavenge in the same way as the ones that do jamesbentley, Thu, 15th Jan 2015