Why Do Sand Crabs Walk Sideways?

Did you ever wonder why sand crabs walk and run sideways? With those big bug eyes, how can they watch where they’re going?

NOTE: Though some of the information below is true of most types of crabs, all of it applies specifically to Ghost Crabs. Along the Emerald Coast these are commonly called sand crabs.

In a nutshell, the reason crabs walk sideways is all about body structure. The little sand crabs you see on Gulf Coast beaches are shaped rather flat and wide. That works well for slipping into a narrow opening or burrowing down into the sand.

It doesn’t work so well for traveling. Crabs can walk forward, but it’s slow going because of their shape and the way their legs are made. The fastest way for them to move is to flex the second joint of each leg. These joints work like our knees and bend only one direction. That direction is sideways, so when a crab wants speed, sideways is the only way to go.

To clarify, humans walk forward because that’s the way our knees bend. Imagine if your knees bent sideways instead. Then we would naturally run sideways too.

The body and leg structure of crabs serves other purposes for them as well. Their physical appearance might seem odd, but it’s what enables them to better navigate the habitats where they live and search for food. For instance, they don’t swim all that well, but they are able to walk quite well on shifting sand or rocky bottoms under water.

Another advantage of having a flat body shape is that it helps them more easily hide either under the sand or in tiny crevices where they can’t be pursued. Their main predators are birds, but on public beaches they also have to watch out for happy, curious kids with nets and shovels.

Finally, moving sideways may be useful as a protective measure. It prevents the crab from exposing the most defenseless parts of its body – its eyes or antennae – to danger.

Can sand crabs see where they’re going?

In a word, absolutely! Ghost Crabs don’t have eyeballs like humans. Rather, they have eye stalks that can rotate 360°. These eyes also see extremely well in the dark.

Day or night their vision is excellent, so they quickly spot impending danger. That’s very evident when you watch them on the beach. They peep out of their holes and wait, watching to see if it’s safe to come completely out. If they detect the slightest hint of danger, they withdraw back into the hole so quickly it’s almost as if they disappear.

How fast can sand crabs run?

According to Allo Culture, crabs can run as fast as 2 meters per second. Animal Spot clocks it at 10 miles per hour. That’s amazing speed, but if you’ve ever seen them run you know it isn’t an exaggeration.

However, given the choice crabs prefer to hide for defense, not run. They also don’t hunt prey, so running isn’t needed for that either.

Other Interesting Ghost Crab Trivia

Did you know…

• Ghost Crabs are omnivorous. Their diet includes both organic matter and animals (clams, snails, small lizards, and even other crabs).
• Mainly nocturnal, Ghost Crabs usually scavenge for food and do home repairs and other activities at night.
• You may not realize that what most of us call “pincers” are actually legs. Crabs have a total of 10 legs, 4 on each side and the two legs with claws that are located near the front of the body.
• Other names for Ghost Crabs are Sand Crabs, White Crabs, and Mole Crabs.
• The holes these crabs dig in the sand run at a 45 degree angle and can go as deep as 4 feet. Each burrow usually has 2 openings.
• Young crabs make their burrows closer to water. Older crabs burrow into the sand farther away from the water.
• The guys are neat. The girls are slobs. Seriously, when females dig a burrow they scatter sand in all directions. Mature males make neat little piles of sand next to their burrow holes. That’s how females find the home of a potential mate.
• Perhaps most amazing is that these crabs can store oxygen in airbags next to their gills. In winter when they hibernate they live off of this stored oxygen.

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