Hermit Crab House Swap

When you have a growth spurt, you probably need new clothes. Caribbean hermit crabs have a similar problem! These land crabs don’t grow their own shells. They usually use empty snail shells for their homes. But as a crab grows, it must move into larger shells.

To be without a shell means doom for a hermit crab. The critters depend on their shells for shelter from the hot tropical sun. So how do hermit crabs find new shells? Sometimes they stumble across an empty one that’s just the right size and they move in. Other times, however, they need help.

When you have a growth spurt, you probably need new clothes. Caribbean hermit crabs have a similar problem! These crabs don’t grow their own shells. They use empty snail shells for their homes. But as a crab grows, it must move into larger shells.

Hermit crabs can’t live without their shells. The tropical sun is hot. Hermit crabs depend on their shells for shelter. So how do hermit crabs find new shells? Sometimes they stumble across an empty one. If it’s just the right size, they move in. But sometimes they need help.

Scientists have discovered that hermit crabs are great at cooperating. When a crab looking for a larger shell finds an empty one that’s too large, it will wait at the shell for hours. Eventually, other crabs crawling around the area show up.

Once the crabs are together, they line up according to size, with the biggest crab first. The big crab moves into the empty shell, abandoning its own. Then, one by one, the rest of the crabs quickly move into the next-largest empty shell. If all goes well, all the crabs end up with new shells that better fit their growing bodies.

Scientists have discovered that hermit crabs are great at cooperating. A crab looking for a larger shell might find an empty one that’s too large. If so, it will wait at the shell for hours. Eventually, other crabs crawl toward it.

Once several crabs are together, they line up according to size. The biggest crab is first. This crab moves into the empty shell. It leaves its old shell behind. The next-largest crab then moves into that shell and leaves its old shell behind. If all goes well, all the crabs end up with new shells that better fit their growing bodies.

This behavior is called a vacancy chain. “It’s similar to the way people try to move into new housing on the same day,” says scientist Randi Rotjan. She discovered this behavior while studying hermit crabs  in Central America. Besides humans, hermit crabs are the only animals known to switch resources at the exact same time. “We think of hermit crabs as funny little creatures, but they have a lot to teach us,” Rotjan says.

This behavior is called a vacancy chain. “It’s similar to the way people try to move into new housing on the same day,” says scientist Randi Rotjan. She discovered this behavior while studying hermit crabs in Central America. Besides humans, hermit crabs are the only animals known to switch resources at the exact same time. “We think of hermit crabs as funny little creatures, but they have a lot to teach us,” Rotjan says.     

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