It seems only appropriate that today’s featured creature should be one that, at first glance, seems a little boring. Hermit crabs are pretty common animals — there are 1100 different species and many of them are kept as pets. Of course, as pets, they’re about on par with seamonkeys or beta fish, the kind of pet that people impulse buy for a couple bucks and expect to be dead within a week. (With proper care, of course, these sorts of animals can live a long time — some species of hermit crabs, for instance, have been known to live over 20 years in captivity.)
Hermit crabs just don’t get a lot of credit for being complex animals with intricate social — yeah, they’re not very hermit-y — behaviors. And frankly, I don’t think we’re appreciative enough of the hermit crab’s particular form of body armor/performance art; unlike true crabs, hermit crabs have no shell of their own, and instead acquire or improvise a suitable home. You’ll find them living in snail shells, stones, driftwood, broken bottles, crab shells, glass shells, and even, apparently, Legos.
Without a shell, they’re vulnerable and also a little funny-looking when they’re naked, just like people. Which is why they armor themselves with the detritus of the sea floor. Basically, they’re like the Iron Man of the sea, if Iron Man was kind of timid and spent all of his time eating tiny things in the ocean.
Which he doesn’t. Because he’s Iron Man. And that’s neither here nor there.
In cases of shell shortage, hermit crabs will fight over shells the same way humans will fight for a decent neighborhood and a jacuzzi bathtub. But give them shells in abundance and they’re practically socialists, as this article in Scientific American explains:
When a lone crab encountered one of the beautiful new shells, it immediately inspected the shelter with its legs and antennae and scooted out of its current home to try on the new shelter for size. If the new shell was a good fit, the crab claimed it. Classic hermit crab behavior. But if the new shell was too big, the crab did not scuttle away disappointed—instead, it stood by its discovery for anywhere between 15 minutes and 8 hours, waiting. This was unusual. Eventually other crabs showed up, each one trying on the shell. If the shell was also too big for the newcomers, they hung around too, sometimes forming groups as large as 20. The crabs did not gather in a random arrangement, however. Rather, they clamped onto one another in a conga line stretching from the largest to smallest animal—a behavior the biologists dubbed “piggybacking.”
I guess that it’s a bit like when you’re a kid and all you get to wear is your siblings’ hand-me-downs (so speaks the youngest child of the family…), but the hermit crabs at least seem happy about it. And sometimes intensely competitive. Here’s a sweet video from Blue Planet with a terrifyingly huge snail, plus some hermit crab combat. The first rule of Fight Club is, you don’t talk about Fight Club.
Speaking of hermit crabs, did you know that coconut crabs are also sort of a hermit crab? In addition, they’re the largest terrestrial arthropod in the world (that means land-dwelling creepy-as-shit crab-thing). They can and do climb trees, live for decades, and have pincers so powerful they can crack coconuts. When the mommy crab and daddy crab love each other and decide to have a family, the female crab releases her eggs into the ocean, where the young ones start out as plankton. As juveniles they do the usual hermit crab thing and find random shells to live in, then when they get older and toughen up a bit they get by with just a thick sort of leathery exoskeleton and put away childish things like shells. Eventually crawl their way back onto land. Despite being the sort of creature you might imagine dwelling in the sea, adult coconut crabs actually drown if they’re left in the water, and so they generally prefer to dwell in your nightmares.