Don’t Shake Hands with a Coconut Crab

A coconut crab climbing a tree, courtesy of Olivier Lejade on Flickr

Have you ever seen a naked hermit crab the size of a steering wheel climb up a tree?

No? Well then, like me, you’ve never met a coconut crab.

Coconut crabs belong to the hermit crab superfamily Paguroidea (more specifically, the terrestrial hermit crab family Coenobitidae). Not only are they the largest hermit crab species, but they’re also the largest land-dwelling arthropod on the planet at almost three feet across! However, it takes a long time for coconut crabs to get that big.

Coconut crab larvae start out as plankton, teeny-tiny animals that are carried around by ocean currents. As they grow, the larvae actually start to eat other plankton, and when they’re big enough, they’ll wear abandoned seashells for protection much like the more familiar hermit crabs we know and love. Soon after, or while still in the shell-toting phase, coconut crabs make their way to shore and leave their water-dwelling days behind them, becoming completely terrestrial and unable to swim. So please, if you do see a coconut crab, don’t throw it back in the ocean. It would not appreciate that.

In fact, you really shouldn’t be touching coconut crabs at all, as these giant crustaceans have the strongest grip strength of all pincer-possessing animals. Coconut crabs are capable of clamping their claws with a force over 1500 Newtons – for comparison, a grizzly bear bites with a force of 1410 Newtons.

So, what do coconut crabs use their crazy-strong claws for? Peeling and cracking coconuts, of course!

Coconut crabs are actually a surprisingly well-named arthropod. I started this post preparing to rename them “tree lobsters” or something, but as it turns out, “coconut crab” is pretty hard to top because these guys really do love coconuts. I mean, they really really love coconuts. They love coconuts so much that if they can’t find any on the ground, they’ll climb up trees to get them. I mean, I’ve seen crabs climbing around on docks and whatnot before, but climbing up a whole tree? And cutting a coconut down from it? That’s serious dedication.

A coconut crab’s left claw is its crusher claw and is always bigger than its right claw, which is used for more precise cutting. Thanks to whologwhy on Flickr for the great photo!

Coconuts aren’t the only food on a coconut crab’s menu. They’ll also eat fruits, other crabs, rats and even seabirds. Yeah, giant crabs eating seagulls… that doesn’t sound horrifying at all. In terms of what eats them, coconut crabs are so formidable as adults that their only predators tend to be humans and larger coconut crabs – that, and they live on tropical islands in the Indo-Pacific Ocean lacking in big animals that would dine on massive crustaceans with trash compactors for hands.

Although they are, in fact, edible, there are a couple reasons why you probably would not want to eat a coconut crab. For one, coconut crabs are a vulnerable species due in part to people overhunting them. Additionally, coconut crab meat can be toxic if the crab has been eating poisonous fruits like sea mangoes. Y’all can take that risk if you want, but I’ll be sitting over here eating my popcorn shrimp basket instead, thank you very much.

So, why are coconut crabs worth protecting? Well, for one, coconut crabs are scavengers that will eat basically anything, making them the perfect island clean-up crew. They’re also a great source of food as larvae, feeding various planktivores, and later feed lizards and amphibians as young coconut crabs. Although a risky delicacy, coconut crabs are still definitely a source of food for people, and their stealing habits are pretty amusing.

Yes, coconut crabs are many things… tree-climbers, coconut-connoisseurs, bird-murderers, and also thieves of random stuff like whiskey bottles and flip-flops, earning them the nickname “robber crabs.” Coconut crabs have a pretty good sense of smell as far as crustaceans go, so it is believed that they steal things that smell like potential food items.

The next time you find yourself somewhere in the Indo-Pacific Ocean, perhaps visiting Madagascar or the Cook Islands, maybe you’ll be fortunate enough to cross paths with a coconut crab. And hopefully it won’t steal your shoes or drop a coconut on your head.

How bizarre that we live in a world where we can say stuff like that about hermit crabs.

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