In this clip from the BBC One series Life Story, Sir David Attenborough narrates a hermit crab housing chain. If you’ve ever had pet hermit crabs, you know they are always on the lookout for the perfect shell, one slightly larger than the one they have because they are growing. But a shell that is too big will be hard to carry around. In the wild, they’ve worked out their own system for exchanging shells of the proper size. Everybody wins! I love how each of them "claimed" the shell they really wanted, as if they had been watching it for some time. After seeing this, I have to wonder if they leave the smallest shells strategically placed near crab eggs for newly-hatched hermits. -via b3ta