Growing hermit crabs are regularly in need of ever larger shells, which serve as mobile homes that protect their soft abdomens. But on this tropical island off the coast of Belize, new shells are hard to come by. When a fresh shell washes ashore, as many as 20 hermit crabs might gather to inspect it. Even if the new shell isn't a perfect fit, these crabs looking to upgrade will stick around, knowing that as soon as the proper sized crab comes along, a chain reaction of shell-swapping will be set off. This so-called vacancy-chain is demonstrated in the video above, which features a clip from the BBC show, Life Story. It's a brilliant sociological adaptation, but as the video shows, it doesn't always work out perfectly for all crabs involved.

[h/t Huffington Post]