Miracles of Weird: The Coconut Crab

Species: Birgus latro

Range: Coastal forests of the Indian and South Pacific Oceans, and the inside of your tent if you’re not careful.

Weird Feature(s): Lives on land, opens coconuts sans hammer, boasts extensive theft record

Oddly enough the coconut crab – which at up to 9 lbs is the largest terrestrial arthropod on Earth – is not a true crab, but rather is the sole animal in the genus Birgus, a group that is related to hermit crabs. In fact, just like hermit crabs, coconut crabs start out dragging half their body around in a shell until they eventually realize they are way too bad ass to worry about anyone messing with them.

All in all, coconut crabs spend almost no time in the ocean. They are are dropped off there as eggs and then spend about a month underwater before heading to land for the rest of their lives. The only problem with that transition is that gills don’t work so well in open air. To draw O2 out of the air, they have evolved organs called branchiostegal lungs – which are effectively inside out gills.

Coconut Crab IP4

One of the more noticeable features of the coconut crab are those impressive thunder thighs. Far from the spindly little legs of ocean dwelling crabs, these muscle packed legs are massive compared to the coconut crab’s body size. Since the land-loving coconut crab can’t rely on the water to shoulder part of its weight – as is the case with legged aquatic critters – it has to fully support its own weight on leg strength and perseverance alone. The super-jacked legs are also helpful in shimmying up coconut trees to harvest coconuts.

Coconut Crab IP 3

As evidenced in Cast Away (2000), coconuts are a bitch to open. Lacking the ability to grip a hammer or the economic sense to buy a pre-halved coconut, the coconut crab has actually been observed carrying coconuts up into trees and dropping them in order to get them open. If they don’t feel like expending that effort, they can manage to go beast mode on the coconut and just start ripping it apart.

Coconut crabs are also called robber crabs, since they have a nasty habit of coming into people’s camps and making off with their belongings. Shiny items like silverware and wrist watches are especially attractive to them. The crabs usually ditch the items after realizing they aren’t food. Marines in WWII reported coconut crabs sneaking into their trenches and making off with bits of gear as well. Maybe they were just stealing out of benevolent curiosity, or maybe the they were secretly trained by Imperial Japan to disrupt U.S. supply lines! Theorize below.

HT: The New Scientist/Zoologger,

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