Animals Wildlife Hermit Crabs Swapping Shells Is a Crazy Remarkable Thing (Video) By Melissa Breyer Editorial Director Hunter College F.I.T., State University of New York Cornell University Melissa Breyer is Treehugger’s editorial director. She is a sustainability expert and author whose work has been published by the New York Times and National Geographic, among others. our editorial process Melissa Breyer Updated November 10, 2020 Share Twitter Pinterest Email Animals Wildlife Pets Animal Rights Endangered Species This is how a group of crabs performs a housing exchange ... if only humans could show such efficiency when it comes to sharing resources! Is it just me or are hermit crabs incredibly charming? Those big eyes and their peekaboo glances, the curious antennae, the skittish scampering ... and of course, the ragtag adoption of funky shells to call home. A group of them together looks like a band of misfits donning makeshift armor, going about their busy business of being crabs. In a perfect world there would be an abundance of shells from which to choose ... but alas, suitable shells are hard to come by. And while the portion of crab that we can see looks pretty tough, the vulnerable soft abdomen curled up in the shell cannot be exposed for very long. (They have a bit of mullet metaphor going on, business in the front and, well something that’s not quite business in the back. As you’ll see in the video below.) Life without a shell is not enduring. So they have come up with an ingenious scheme. When a crab happens upon a shell, it scopes it out – and when it is too big, the crab sits and waits, sometimes up to eight hours. More crabs show up to check out the potential new digs, and for those whom the shell is too big, they line up and wait. And get this, they line up in size order. Up to 20 crabs, lined up biggest to smallest, waiting for just-the-right–size crab to appear. And when the Goldilocks crab shows up, things get nutty. He or she sheds their shell and takes up the new one, and each crab of successive size hops out of their old shell and into the larger one ahead of it. Wow. Known as a vacancy chain, it’s a term originally used by social scientists to describe a way that people trade resources. But to be honest, I’ve never seen a group of people do it as effortlessly as a bunch of hermit crabs. You can see it all unfold in this wonderful BBC1 video, consider it a lesson from the crustacean world.