On the Move A crab has to be really strong to carry its exoskeleton everywhere. T at’s why it’s developed so many legs. Five pairs stick out from its sides. Most use eight legs to move. Some crabs can move amazingly fast.


Take a ghost crab, for example. When I first spot this pale crab, it’s tiptoeing sideways across the sand. Its eyestalks stick up like a periscope on a submarine. With compound eyes at the tip of each stalk, it can see all around its body. T at makes it hard to sneak up on a ghost crab. I’m trying to, though. Suddenly, it sees me and takes off . Its


pointy legs grip the sand, letting it zigzag without slipping. I sprint aſt er the crab to catch it. I’ve almost got it! I dive into the sand, my hands outstretched—and catch air. T e crab zips into its sandy burrow, safe.


I’m used to losing this race. T e ghost crab is one of the fastest crabs, able to run 16 kph. I catch a ghost crab once out of every 10 tries.


Lots of Legs Other crabs use their legs in other ways. A swimmer crab, for instance, doesn’t run. So instead of having pointy legs that grip the ground, it has flat hind legs. T e crab uses these legs like paddles to swim. A frog crab has flat back legs, too. It’s fun


to watch what they do. One moment, you see the crab. T e next, it’s gone. It’s used its legs like spades to dig a hole to hide in. T en there’s a sponge crab. T is crab uses


its legs to hold a sponge on its back. T e crab looks like it’s wearing a funny hat. In fact, it’s using its environment to stay safe. T e sponge camouflages the crab. T e sponge also tastes bad, so predators stay away. Other crabs carry stinging fire urchins or sea anemones on their backs. T ese crabs all use their legs and what’s in their environment to survive.


8


In a Pinch A crab’s first set of legs look diff erent than all the rest. T ey end in pincers, or claws. T ese claws grab and pinch. T ey help a crab survive no matter where it lives. A crab can fight with its pincers. More


oſt en, though, it uses them to eat. Some crabs have pincers strong enough to crush shells. Others use them to spoon sand into their mouths. T ey use their mouthparts to suck off bacteria and then spit out little sand balls. Some crabs even use their claws to “talk.”


I like to listen in on male fiddler crabs. A male has one giant front claw and one little one. It waves the big claw in the air and drums it on the sand. T at lets other crabs see and hear it.


More to Learn We’re still discovering new ways crabs use their parts to survive in their environments. T e Yeti crab is a good example. It lives deep in the ocean. Finding food is hard there. We recently learned that this crab uses its hairy claws to catch bacteria. T en it grows more bacteria on the hairs. T is crab has developed a way to use its body to farm food! Crabs all have the same body plan, yet I see


so much variety. Each species has developed variations on their body parts to survive in their environment. Seeing that in action still makes my jaw drop in awe and wonder.


Wordwise


anatomy: the parts that form the structure of a living thing


exoskeleton: a hard supporting structure on the outside of a body


invertebrate: an animal that lacks a backbone


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