More than 65 million years ago, the hermit crab, which is more closely related to certain kinds of lobsters than “true” crabs like the blue crab, basically invented the mobile home. Using its soft, spiral tail, it will quickly back into empty snail shells or even small bottles it finds on the ocean floor.
Why has this way of life been so successful for hermit crabs?
No one is sure, but here’s one guess:
Although many predators, including fish with strong molar-like teeth, can bite into a more conventional crab (Yum! Crunchy on the outside, soft on the inside), a hungry predator needs some serious jaw strength to crush a snail shell. A periwinkle shell, for example, provides an incredibly strong house and home, engineered into a roughly spherical, spiral form that withstands structural stress.
Perhaps the hermit crab saves metabolic energy by avoiding the need to build a shell around its tail-like abdomen.