Giant Crabs

The Japanese spider crab is harmless to people. But it might not look that way if you happened across it at the bottom of the Pacific Ocean. It can span 12 feet—the largest known crab on the planet.

The crab’s hard body is typically about a foot long, and the crab weighs 35 or 40 pounds. It has 10 legs. Eight of them are for walking along rocky ocean bottoms. The other two hold powerful claws. The claw legs are longer than the walking legs on males, but shorter on females.

Japanese spider crabs spawn in fairly warm, shallow waters, primarily off the Pacific coast of Japan. Juveniles are pretty small. As they reach adulthood, though, they grow to giant proportions. And they move to deeper waters—generally a few hundred feet to a thousand feet or deeper.

The crabs can’t swim. Instead, they scuttle along the bottom looking for food. They nab small fish and crack open clams. They also scavenge for dead animals, and scrape algae off the rocks.

Because of their size and hard shells, the crabs face few threats—mainly from fishers, because they’re considered a delicacy in parts of Japan. And they’re well disguised—their mottled, spiny appearance blends into the background. Just to be safe, though, juveniles sometimes disguise themselves. They pluck bits of kelp, sponges, or other organisms. They chew on them for a little while, then stick them on their shells. That helps keep these imposing but harmless creatures safe at the bottom of the Pacific Ocean.