Second-hand shells provide shelter for hermit crabs, giving their soft bodies extra protection from predators. But the crabs frequently need to find new homes as they grow bigger. Even if an empty shell is unsuitable for a hermit crab’s latest size requirements, they don’t carry on their house hunt elsewhere. Instead, they wait for other crabs to see the shell.

The scene was filmed on a small Caribbean island off the coast of Belize, where the supply of suitable shells is limited. As a crab waits beside an abandoned but oversized shell, more crabs soon show up. They take a look around the shell, but finding it to be far from their wants, begin inspecting the other crabs’ shells.

Soon a queue of house hunters forms in size order, all waiting for the “housing chain” to be completed by a bigger crab snapping up the new shell. Finally when such a crab arrives, the ‘chain’ sparks into life as the crabs vacate their old shells and climb into their new homes.

The clip is from BBC One’s Life Story.