Golden ghost crab (Ocypode convexa) This species, endemic to Australia, can walk sideways like many Brachyurans. Ghost crabs are one of the fastest crab species in the world, capable of achieving a speed of 10 miles (16 km) per hour when running on land. (more) Why Do Crabs Walk Sideways? Written by Manjishtha Bhattacharyya Manjishtha Bhattacharyya is an editor at Encyclopaedia Britannica. She holds a PhD in zoology from Vidyasagar University, West Bengal, and has more than seven years of experience in science communication... Manjishtha Bhattacharyya Fact-checked by Britannica Editors Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree.... Britannica Editors Last updated Mar. 20, 2026 •History There are two aspects to this question. The first concerns the mechanics of crab motion—the how—which evolutionary biologists call a proximate question. The second concerns the function of crab motion—the why—which evolutionary biologists call an ultimate question. Before delving into why crabs move sideways, let’s first take a look at how they do it. To answer how crabs walk sideways, we have to look at their body plan. Crabs have a flat body with five...

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