Image: Momoko Igawa The life of a hermit crab is one of repetition. Find an abandoned snail shell. Live in it. Nom on some flecks of detritus. Grow bigger. Find a slightly bigger shell.

Sometimes when a new shell turns up, hermit crabs will form a line, biggest to smallest, to see which animal fits the new shell. The next smallest will take that crab’s hand-me-down home, and so on.