I thought I was pretty much up to speed when it comes to the topic of hermit crabs upgrading their shells. Outgrown the one you're in? Just find a bigger, emptier one and move on in. But it turns out that hermit crab home swaps are a whole lot more complicated than I'd ever imagined - and a whole lot more organised!

The footage above, which is a newly released teaser for episode 3 of BBC's new David Attenborough-narrated documentary, Life Story, shows what a handful of hermit crabs on a tiny Caribbean island off the coast of Belize have to go through as they attend, quite literally, to some housekeeping matters. 

One of the biggest problems with my half-baked assumption that hermit crabs wandered around all day in hopes of stumbling upon the perfect empty shell is that, just as it is in the human world, finding the perfect home is by no means easy. In reality, these little crustaceans are much more likely to come across an empty shell that's too big or too small for them. If it's too big, they'll sit right next to it and wait.

Eventually more hermit crabs in the market for a new home will show up near the big, empty shell. While they wait for someone big enough to move in and vacate its own, smaller shell in the process, the group will organise themselves from largest to smallest, each one grabbing onto the back of their larger peer in front. 

Once a big enough crab arrives and hoists its weird, peanut-shaped body out of its original shell and into the big, empty one, a chain reaction will be triggered - each crab down the line is now hurrying into the shell that's been vacated by the crab in front of it.

Which all seems pretty civil so far, but then a nefarious late-comer shows up to threaten its rival with homelessness, death and destruction. What happens next? We don't want to spoil the ending, but if you've never felt bad for a hermit crab before, you will now.

Source: Twisted Sifter