Claws: The Ultra-Jumbo Class of Crustaceans

Last month, the U.S. media engaged in a bit of a kerfuffle over a particularly beefy lobster that had been pulled out of the ocean at the Bay of Fundy. At some 23 pounds and an estimated near-century of life on this planet, the king-size crustacean is a worthy subject of a perennial news cycle that manages to somehow focus on monstrously outsized shellfish. The Fundy lobster isn’t alone, and is one in a line of many other big buggy bastards from all over the world that have received attention by tipping the scales at 20 or 30 pounds or more. The reasons why knowledge of humongous lobsters eventually ends up being mass shared are because 1) it happens to be a slow news day, 2) photos with people alongside lobsters posed in forced perspective to make them look even larger are awesome, and 3) it’s damned impressive, considering the average lobster that makes it to Red Lobster’s Spectator Tanks of Inevitable Death is only two or three pounds, a fraction of the size of these animals.

This is great and all, but our planet is populated with entire species of crustaceans that reach strikingly, unexpectedly insane proportions as a part of their normal biology. Perhaps the most famous, and most recognizable of these is the Japanese spider crab (Macrocheira kaempferi), an unsettling, spindly, deep-sea demon that looks like the end result of the Slender Man impregnating a shrimp, and at their largest, can outweigh your samoyed and bear hug a Ford Focus.

“AHHH, what the hell! Sorry, sorry, sorry…I’ll make sure to knock next time!”

But there are other crustaceans slowly shambling about under the waves, along sandy beaches, or even in familiar rivers and streams that are strikingly massive, and get comparatively little attention, despite being some of the biggest, crustiest, clicky-clacky pinch-mongers around.

One of these is the Tasmanian giant crab (Pseudocarcinus gigas), a species that, as its name indicates, is found in the cool waters over the continental shelf of Southern Australia and into the waters surrounding the northern coast of the island of Tasmania (in particular, the Bass Strait, the ribbon of ocean that runs between the island and mainland Australia). As far as overall appearances go, the Tasmanian giant crab isn’t bizarrely constructed like its distant cousin, the Japanese spider crab. It looks very….well…crabby. Broad, oval, shield-shaped carapace splashed with red with creamy white underneath, a pair of clawed arms, a bunch of short, bendy legs, stubby, twitchy mouthparts and feelers…..pretty standard as far as crab features are concerned. Pretty standard for its closest relatives as well; Pseudocarcinus gigas is the only member of its genus on Earth, but other members of its family (Menippidae) abound, and are often referred to as “stone crabs” for their stumpy, rounded, boulder-like body shape (one of them, the Florida stone crab (Menippe mercenaria), is popular as human chow in some regions of the southern U.S. and Caribbean).

The thing that makes ol’ P. gigas stand out from the crustacean crowd is what’s inferred by its species name, “gigas“, which literally means “giant.” Pseudocarcinus gigas gets big. It gets really, scary big. How big is “scary big”? Let’s just say that if the Krusty Krab was owned by this brachyuran behemoth, Spongebob would be continually shitting into every literal corner of his pants.

“Keep those patties comin’, boy, or I’ll cut ye asshole to gullet! Yek yek yek yek!”

The biggest Tasmanian giant crabs can weigh as much as 30 pounds, and have carapaces broader than the wheels of many cars, which is more than a little fucking horrifying. I become sweaty and uncomfortable when something very similar to the thing I crack open and delicately serve with mayo, citrus, and greens looks like it could clip off my arm and beat me with it. Seafood has no business being that big. I mean, these Tasmanian titans can grow as heavy as a human 2 year-old….and when picked up, nearly as ornery as one.

“Auuuugh! Who do you work for?! Is it Silver? Captain D? Joe? Tell Joe I’ll splinter his femur AND his goddamned, precious Shack!”

By far the most bladder-emptyingly intimidating trait of Tasmanian giant crabs are their asymmetric claws, one small and one large, something they share with many other members of their stone crab family. One of their claws is a wicked, armored machine of mythic proportions, a bony cage harboring more rippling muscle than what graced the forearms of a heyday Arnold Schwartzenegger, capable of shattering snail shells and human hands alike….and then there’s the “big” claw. The “big”, right-hand claw is a ridiculous, Mephistophelean apparatus, massive to the point of being grotesque, like some kind of unholy, supernatural mutation. Like the crab got caught stealing clams from Ursula the Sea Witch’s garden or whatever, and she cursed him with some kind of unsightly crustacean elephantiasis as punishment. This claw is armed with preposterously elongated, sharp, black tips that arc across each other like the long, unclipped fingernails of old-school Chinese aristocrats. I’m convinced this outsized pair of meat hook scissors is limited to a single specialized function: carving into the bellybuttons of mortals and removing the very souls from their bodies.

When the Terror-crab asks for a light, you better damn well give that bastard your lighter. Don’t ask for it back. Just leave.

It is perhaps of little surprise that Tasmanian giant crabs are widely regarded to be, mass-wise, the second largest crab species in the world (right behind the Gaunt Sea-nightmare I outlined briefly above)…and that when the opportunity arises, people can’t help themselves from taking photos of these things wearing normal-sized crabs as hats.

If you’ve been looking at Captain Living-Compulsive-Masturbation-Joke up there and thinking that beefy, super-swole right claw would look better split open and dunked in warm garlic butter, then you’re in luck. Tasmanian giant crabs are quite edible and there’s a small-scale fishery of these crabs in Tasmanian waters. However, if you’re a Yank like me, and are hoping to swing by the local Costco and pick up a gut-busting quantity of fresh Pseudocarcinus gigas deliciousness (probably marketed as “Tazzie mammoth crab” or something ridiculous like that), you’re going to be pretty disappointed. The annual harvest of this species is very limited, export tends to be local in scope (basically the rest of Australia and into East Asia), and the boutique nature of the fishery tends to make the crabs expensive (like 50 bucks per pound)….and that’s a good thing. Tasmanian giant crabs, despite their girth, don’t really eat that much or that often, wandering across the muddy ocean bottom, grazing slowly on the occasional carcass, unlucky mollusk, or smaller crab or shrimp. This laid-back attitude towards getting enough food energy to develop means that they grow and mature very slowly. This makes them incredibly susceptible to overfishing, since they can’t replace their numbers quickly. Strict fishing regulations are, fortunately, in place to keep populations from getting depleted.

But, if you were to make a special trip to the northern shores of Tasmania to get your hands on some of that delectable, rare, sustainably-fished giant crab flesh…you could see the second crustacean on this list just by walking inland, up into the wet, thickly-forested valleys of the island. Yes, Tasmania is host to two exceptionally huge crustacean critters, and this one lives in freshwater.

Meet the Tasmanian giant freshwater crayfish (Astacopsis gouldi), which was also known as the “tayatea” to some of the aboriginal peoples of Tasmania.

“On my way to steal your girl…”
(all giant crayfish gifs generated from this excellent conservation-themed short film entitled “Looking After Our Rivers” by Mark Pearce)

These stout, black-shelled, stream-bound lobsters are far and away the largest species of crayfish on the planet. How big are they though? Try THIS big.

Hooooly shit.

Nope. Nope nope nope nope.

At roughly the same size and heft as your neighbor’s cat, Flufferbell, a full-sized, adult tayatea is not only the largest crayfish in the world, but also the biggest freshwater invertebrate, period, currently in existence. In the past, there were reports of these crayfish growing as long as a human leg and heavier than a holiday ham, but these days, most tayatea are considerably smaller…yet still massive and intimidating enough to look more like the aliens in District 9 than something thrown into a pot of jambalaya.

The Tasmanian giant freshwater crayfish is, unsurprisingly, found only on the island of Tasmania. Even more specifically, it natively inhabits only the lowlands in the wet strip of territory at the northern end of the island, and is limited entirely to the streams and rivers in this area that flow north into the Bass Strait (the same body of water where the previously outlined giant crabs are plentiful). However, in recent decades, this range has gotten even smaller, and now the Tasmanian giant freshwater crayfish is typically only seen in fragmented sections of rivers in the northern part of the state. In the past 50 years or so, this strange, lobster-sized crawdad has seen a 70% decline in geographic range and its estimated population size has plummeted to about one fifth of its former glory.

Astacopsis gouldi is as endangered with extinction as it is gargantuan…a direct result of a combination of human influences and quirks of this animal’s biology.

When it comes to having traits that would help ensure survival in a world overrun with smart, hungry, city-raising, forest-leveling, farm-tilling primates, evolution gave the tayatea the shit end of the stick. First off, these giant crayfish are little more than slow, placid, white, succulent protein encased in a mildly inconvenient crunchy wrapper, each one large enough to feed an entire family in a pinch. When large numbers of European colonists began to settle in Tasmania, it didn’t take them long to take advantage of the rivers that were chock-full of living, breathing embodiments of a Cajun restaurant owner’s wet dream. The crayfish were pulled out of the waterways as a delectable and easily-caught foodstuff for many decades by the European settlers, but the harvest wasn’t even close to sustainable. Not even in the ballpark of sustainability. Actually, it wasn’t anywhere near the county containing the street where the ballpark of sustainability is located. It wasn’t necessarily the volume of crayfish taken by itself that was the issue, but the fact that, for the second strike against their luck, much like the giant Tasmanian crabs, the tayatea are particularly vulnerable to overfishing (and for many of the same reasons). Tasmanian giant crayfish take forever to reach reproductive maturity. Most species of crayfish that are collected by humans for food take between one and three years from hatching to finding a crayfish that shares its goals and interests, settling down, losing track of what music is popular these days, and churning out a bajillion chitinous kiddies. But Astacopsis? Males take somewhere in the neighborhood of nine years to get their gonads up and running, while females take something like fourteen fucking years to reach reproductive maturity. This reproductive procrastination is not so much that tayatea are the Peter Pan’s of the crayfish world, stubbornly refusing to grow the hell up and make their mothers into proud (and finally satisfied) grandmothers, but that they are late bloomers; reproductive maturity in crayfish is typically tied closely to size, and tayatea grow incredibly slowly by crayfish standards, and therefore their entire developmental lives are stuck behind a bus on the scenic route. This leisurely growth rate becomes a problem when individuals are pulled out of the population at even a modest pace, because it doesn’t take much to outpace the crayfish’s ability to replenish their numbers. Slow growth and/or maturation rates are a major factor contributing to the population depletion in many other animals (an example that comes to mind are sharks; many currently threatened or endangered species can take more than a decade or two to reach reproductive maturity, and once they do, they may not produce many offspring at all in their lifetimes).

The third trait working against the modern, post-European settlement survival of the tayatea is also associated with how these crayfish make babies. Not only do female giant crayfish take as long as humans to reach reproductive maturity, but once they do, they spend their lives with as much libido as a panda on SSRIs. Females will only spawn every other year (in the autumn), and grip the fertilized masses of eggs underneath her tail and against her legs until the next goddamned summer. That’s right, tayatea eggs take a full nine months to hatch. Even after anywhere between two hundred and one thousand less-than-giant crayfish come into the world, they stick close to Mom for another several months. So, a mature, female Tasmanian giant crayfish spends half her time “pregnant” or babysitting, and the other half not breeding. Fifty percent of her time actively reproducing may not seem that low, but the key is the long period of time our aforementioned lady crayfish spends directly caring for or incubating her single batch of offspring for the two-year cycle. The strategy of Tasmanian giant crayfish keeping eggs and babies on their person for a year at a time is, normally, a fine one. Once at reproductive size, giant crayfish are too large to have any natural predators that would threaten the lives of their clutch. Platypus and some species of fish are known to prey upon younger crayfish, but the big, honking, bowling ball-sized full grown monsters can contently take their time raising up the next generation. Humans, however, have no issue catching and eating adult crayfish….payload of eggs and all. What is normally a perfectly adequate reproductive gameplan, evolved in relative isolation from large crustacean-eating animals, becomes a grave drawback as soon as humans and their appetite for literally anything remotely vulnerable are thrown into the mix.

Historically, it was primarily the swift and unregulated direct overconsumption of these crayfish, enhanced by their slow growth, maturation rate, and long gestation times, that led to their fall in numbers. Since 1998, the harvesting of tayatea has been entirely illegal (without a special permit) in Tasmania, and there is hope that their populations will rebound in coming decades as a result.

However, this species is still at risk of extinction from habitat loss. This is where their fourth unfortunate trait comes in; Tasmanian giant crayfish are, much like that one roommate you briefly had in college, completely unable to compromise on their ideal living conditions.

“No, Derek, I don’t care that it’s ‘Fruit Loop Friday’. Do you want ants? Because this is how you get ants, you weird little shit.”

Astacopsis gouldi is a picky, finicky bastard when it comes to what is and what isn’t acceptable real estate. The streams in which these crayfish flourish need to be shaded with lots of riverside vegetation, and be crystal clear and clean. Preferably, the water should be relatively cold with high oxygen content and negligible amounts of sediment. Basically, if they aren’t sitting in a creek that looks like it was poured directly out of a chilled Brita filter, they ain’t happy or healthy, and will probably die as a result. So, you may be thinking, just keep pollution out of the rivers, and they’ll be fine. What’s the big deal? Isn’t northern Tasmania not exactly a juggernaut of industrialization (which would allow for the opportunity for waterway waste pollution to be a major issue)? Well, there is habitat degradation, but it’s indirect. The cause is large-scale, clear-cut logging operations that occur upriver near the headwaters of these drainage basins. The rivers and streams become swamped with mud and runoff, which chokes out crayfish downstream. Reduction of streamside vegetation (sometimes from direct deforestation, but also as a consequence of flooding and erosion caused by upstream activity stripping the riverbanks of any absorbing vegetation) has the effect of removing shade, which causes the water to heat up past tolerable temperatures, and for oxygen levels to drop (since oxygen does dissolve as easily in warm water). A lack of large plants and trees near these waterways also takes food right out of the mouths of these regal crustaceans. Tayatea consume rotting wood (and the bacteria that grows in and on it) as a major component of their diet. Leaving streams bare, silty, and hot effectively takes away the habitat and food sources of giant crayfish to the point where they cannot adjust, and are simply driven out of that drainage basin altogether. On top of all of this, in lower elevations, habitat loss from humans setting up farmland and diverting water is another strike in the chest of this species. Roads and culverts create additional problems, as they make moving between streams and finding new or adequate habitat next to impossible. So, if you’re ever traveling around the majesty of northern Tasmania, pulling over in your car to gander at the sights and check your map, and you’re feeling just a little too happy with yourself…just think about how the paper map in your hands potentially got its start in a forest up in the mountains, now mulched down to the dirt, leaving scores of crayfish downstream starving, baking, asphyxiating, and disoriented in a milky, dark slurry that was once their pristine home.

If you’re wallowing in impotent self-loathing and the futility of appreciating biodiversity in a dying world clap your hands…

Recovery efforts for this biggest of crayfish are slowed and complicated by a number of factors. Many regions in northern Tasmania are too far gone to hold any hope as a place of reintroduction; the streams having been drained for agricultural purposes a major stumbling block. The majority of the remaining range of this species exists on private land, which is largely used for lumber and agriculture, unsurprisingly, and is largely unfit for tayatea, assuming any high numbers still exist there. The best hope going forward for the Tasmanian giant crayfish comes from the small pieces of protected forestland in the Tasmanian wilderness, immune from deforestation, but until a direct series of measures are implemented to target the preservation and recovery of this species via habitat preservation, it’s uncertain how long they can evade extinction. Effective management will likely require additional behavioral knowledge and population surveys to determine where and how efforts will have the greatest impact. In the end, this tug-of-war between resource development and the health of river ecosystems is very reminiscent to me, as a former resident of the Pacific Northwest, of the convoluted history of salmon and the introduction of dams used to generate hydroelectric power. But, whether or not dramatic actions on par with dam removal will eventually be employed to save the endangered tayatea remains to be seen. I’m cynical, mostly because in the case of the Northwest’s salmon, the fishery is of huge economic interest; protection of habitat is actually of direct human interest. Tasmanian giant crayfish are unfortunately a vulnerable evolutionary curiosity and cannot play the role of “widely-harvested foodstuff”. Perhaps a better comparison between this crayfish’s plight and a threatened critter directly catty-corner across the Pacific is the famously down-on-its-luck (and divisively protected) northern spotted owl, an animal directly threatened by logging and the encroachment of agricultural land, but without an immediately tangible economic benefit gifted to humankind through its continued existence.

It’s worth mentioning that while the Tasmanian giant crayfish is superlatively impressive due to its size, Australasia in particular has quite a bit to offer in regards to unique crayfish. Mainland Australia, Tasmania, and New Guinea are a global center of crayfish diversity, with more than 150 species of crayfish patrolling the brooks and rivers of Australia alone. In particular, one family, the Parastacidae, is diverse and widespread across Australia. The family is known only from the “southern continents” (Australia, South America, southern Africa, and Madagascar), having a “Gondwanan distribution” (referring to the supercontinent of Gondwana, which was made up of these southern continents plus Antarctica, breaking apart nearly 200 million years ago). The Tasmanian giant crayfish is a member of this family, as is another sizable crayfish, the Murray crayfish (Euastacus armatus). It is found through much of the lower stretches of the Murray and Murrumbidgee Rivers in southeastern Australia, and grows to lengths of over a foot, making it the second-largest crayfish species in the world, beaten out by its close relative from the island of Tasmania. It’s a pale-clawed, thorny creature that looks like it crawled out of a pixelated puddle in the Super Mario Bros universe. It, like the Tasmanian giant crayfish, has suffered range reductions and population shrinkage as a result of fishing pressure.

All the colossal crustaceans mentioned above are either primarily, or entirely, aquatic. Their immense bodies are supported by water, and when pulled to the surface, despite their impressive/terrifying appearance, they can do little more than weakly flip themselves on their back and wave their useless legs like an air traffic controller on barbiturates. They are fine-tuned, armored machines when submerged, but when they feel gravity’s full effect and the desiccating air on their gills, they suddenly have the grace and energy of a hungover vertigo-sufferer trying to haul themselves out of a bathtub.

However, one species of crustacean has looked at the shimmering ceiling of its watery world, girded its loins, and taken the landlubber life by storm. This crustacean is not only the largest terrestrial crustacean in the world, but it is also the largest arthropod (the taxonomic phylum that contains everything from insects to centipedes to shrimp) to skitter about in the dirt in modern times. They are known by many names across their geographic range, including ‘coconut crab’, ‘robber crab’, and ‘palm thief.’ In the Mariana Islands and Guam, it is known as ‘ayayu.’ In the Eastern Caroline Islands, it is called ’emp’, and in the Cook Islands, it is called ‘unga’ or ‘kaveu.’ All of these names describe Birgus latro, an animal that looks like a combination of evolution’s take on the chitterskrags from the Dungeon Siege games and something that I’m pretty sure plants nightmares in your brain by whispering ever so softly in your ear as you sleep.

“Sshh, rest your head, delicate, mortal creature. May your slumber be….fruitful.”

These terrestrial crabs are found widely across the tropical Indo-Pacific region, ranging from the island of Zanzibar off the coast of East Africa at the western edge of their distribution, through the Indian Ocean and the scattered islands of the West and South Pacific. Despite their wide range, coconut crabs are fairly rare in areas with large human populations, with their largest populations situated in isolated island chains and coral atolls out in bumfuck nowhere in the middle of the goddamn ocean. The reason for this is almost certainly because humans are eating these critters out of existence wherever enough humans establish and overlap with crab’s territory. In fact, it is thought that they, at one time, were also found on the Western Indian Ocean islands of Mauritius and Madagascar, as well as the Australian mainland, but that humans in these areas simply om nom nomed them into a state of localized extinction (it’s also curiously absent from the Hawaiian Islands for an unknown reason, and when one recently turned up wandering aimlessly through Honolulu just down the road from where I live, the public/media response was one primarily concerned with its invasiveness…although it’s also possible it existed here before Polynesian colonization).

Perhaps this ‘extirpation by digestion’ is understandable, considering that in the tropical island locales that these crabs are natively found, there isn’t much food to eat anyways, so local populations would force themselves to dare subduing and splintering open an alien horrorshow that looks more like a demon-possessed Pokemon than a meal. But, there must be some other reason humans would risk cracking open something that looks like it scrambled out of a fresh, mysterious, meteorite impact crater. There is. Coconut crabs are easy to catch, and, despite looking like they having nothing inside but the souls of thousands of missing children, they are, in fact, full of succulent, delicious flesh. Shitloads of it. Because, as I said above, they are really big. And, to drive home what it means when I say “largest land-living arthropod on Earth”, I’ve included this oft-shared image of a coconut crab forever enshrining a newfound appreciation for the good, normal, God-fearing, nocturnal, unsanitary, kleptomaniacal mischief of raccoons.

I’ll take squealing, furry balls of teeth and rabies over an honest-to-Christ living Ray Harryhausen creature effect, thanks.

Coconut crabs, at their largest, can have a leg span of three feet and weigh as much as a 12-pack of whatever alcoholic beverage you’ll need to pound down to deal with this information. If you’re visiting one of the areas where coconut crabs live, and you think you can avoid seeing one of these guys by just skipping the beach, well, I’ve got news for you; coconut crabs are fully terrestrial, can march their creepy asses several miles inland, and are surprisingly, terrifyingly nimble over open ground. Also, did I mention they can climb trees? Because that’s sort of a thing they are known for. Shimmy-ing your quaking knees up a palm tree is a pretty fucking futile escape tactic. But remember, if you’re thinking at this point that your god has forsaken you and that surely these abominations are the incarnations of Old Scratch himself, know that they are NOT one in the same; one is an ancient, uncaring reservoir of malice and betrayal, a twisted being descended from a regal lineage…and the other is Satan.

Well, at least one of them is a shiny.

Birgus latro‘s unsettling size and otherwordly, death-spider appearance has been acknowledged mostly by, admittedly, comparatively hysterical and easily-petrified Westerners for a while now (the people of the tropical Indo-Pacific that lived alongside coconut crabs largely regarded these animals as delicacies and aphrodesiacs). In particular, coconut crabs were forced into the consciousness of American life during the Second World War when Allied forces were scattered across much of the West and Central Pacific, and American soldiers came in contact with these armor-plated monsters on their remote island outposts. The impact coconut crabs had on these men can be seen in the stories and imagery that made it back home in the decade after the War. For example, this was a beast so unnerving, apparently, it inspired artwork (and associated tales of terror) featured in hypermasculine, vintage “men’s adventure mags” in the 50s, much like the George Gross piece below, which was featured on the cover of the November 1956 issue of Man’s Conquest. For context, this was a publication so devoted to stories of egregiously haggard badasses upholding Man’s glorious dominion over nature by shooting, spearing, roundhouse kicking, or otherwise dispatching a veritable zoo of inexplicably numerous and murderous wildlife that I’m half-convinced the magazine owes its existence to the ghosts of Teddy Roosevelt and Ernest Hemingway aggressively ejaculating onto a stack of blank pages. The 50s and 60s were….uh….a different time.

“Christ Almighty! These are the second-worst crabs I’ve ever had to deal with…next to the ones I got from that dame the last time I was in Tijuana with the boys!”

The coconut crab’s great size becomes even more impressive when you consider the evolutionary history of this crustacean, and all the truly unique adaptations and modifications to its physiology that have been driven by natural selection.

Birgus latro is literally one of a kind. There is only one known species in the coconut crab genus, and its closest living relatives might not be what you’d expect. Rather than its nearest kin being other big, brutish beasts like the other “giant” crabs and crayfish I’ve gone over earlier in this blog post, the coconut crab comes from diminutive stock. Coconut crabs are actually a variety of ludicrously huge, highly-derived, “homeless” hermit crabs. Coconut crabs are members of the family Coenobitidae, which includes a single other genus (Coenobita). Coenobita hermit crabs are notably robust and very capable land-dwellers themselves, but of course, the elephantine black sheep of the family takes this to a whole other level. The family resemblance is still quite there, and this is especially true when you pull down the coconut crab baby photos from the attic. Juvenile coconut crabs, following a larval stage in the ocean, are functionally the same as Coenobita hermit crabs. In their youth, coconut crabs hold onto their heritage tighter than a woefully misguided South Carolinian waving the Stars and Bars; they cover their soft hindquarters by retreating into, and carrying around, a snail shell. It is only after they have grown larger, too large for any shells or even coconut halves, that they forgo their protective training wheels altogether and start strutting about in a thick, desiccation-resistant carapace. I was in the Republic of the Marshall Islands (a Micronesian nation of coral atolls in West Pacific) earlier this year, and I saw a young coconut crab on a beach on Arno Atoll without even knowing it. At the time, I assumed it was a Coenobita species, but it was months later when I was looking at the photos and attempting to identify the species that I realized no native hermit crabs were a match, and the coloration was a dead wringer for a fledgling Birgus latro. The one I happened across was using an ill-fitting piece of plastic pollution as a shell, which should have tipped me off, considering that everyone knows that, of the two crab groupings, young coconut crabs have the inferior sense of fashion.

You’re wearing plastic? Really? Hydrocarbons are SO last season.
Photo: Jake Buehler

So, coconut crabs are just hermit crabs that hit the gym and creatine powder really hard and ditched the mobile home to grin and bear it out in the big, harsh, idyllic, balmy, sunny, white sand beaches. It’s worth observing that hermit crabs, as a group, aren’t really “true crabs” either. They belong to a division of crustaceans (an infraorder, in this case) called Anomura (meaning “differently-tailed”), whereas “true crabs”, which include all the crabs you are likely most familiar with (including the giant Tasmanian crab), are in the infraorder Brachyura (“short-tailed”). Other Anomurans include squat lobsters, mole crabs, and king crabs (which includes this star of Deadliest Catch). Anomura and Brachyura are thought to be “sister groups”, meaning they share a common ancestor more recently than with any other similar division of crustacean.

Outside of their size and libertine views on hermit crab domestic traditions, coconut crabs have evolved a number of traits that not only make their terrestrial lifestyle possible, but required. For one, coconut crabs have modified their gills into a brachiostegal lung, which consists of gill tissue with a high degree of surface area to allow absorption of oxygen from the air rather than from water. The setup, not unlike the interior workings of your own respiratory system, must be moist to function well. However, unlike you or I, the coconut crab doesn’t have a whole series of cavities and sinuses and tubes to facilitate the retention of moisture, so it uses a rather crude (but effective) method: wetting its legs in a puddle and stroking them over the convoluted lung tissue. Although these lungs need to be constantly spritzed, this doesn’t mean an adult coconut crab can breathe in water just as easily as in the air. Their branchiostegal lungs are indeed lungs, and a submerged coconut crab is guaranteed to drown. Adult coconut crabs are so incapable of dealing with water that after mating on land, the female carts around the fertilized eggs underneath her tail until right before they hatch, and when the time is near she makes a trip down to the water’s edge with the haste of someone hunting down a public restroom after a gastronomically reckless episode with a gas station burrito. There, she can wash her young into the surf at high tide while hardly getting wet.

Coconut crabs have a varied and entirely terrestrial diet, which, as you’ve likely guessed, includes coconuts. These crustaceans really can, and do, break through the tough exteriors of coconuts to eat the nutritive white flesh on the inside. It sometimes takes the work of more than one crab at a time, but they are more than capable of using their strong claws to strip away a coconut husk like you would feverishly denude a Kit Kat bar of its wrapper (and by you I mean me…far more often than I’m proud of). Breaking apart the inner core occurs in small pieces, and splitting the whole thing open can take days, but an animal with a brain the size of bouillon cube can do it with its bare hands and that’s more than I can say for myself. If coconuts aren’t already sitting on the ground, and a coconut crab is in the mood for some Mounds and piña colada action, the hungry bastard will summon its inner Sylvester Stallone ala Cliffhanger and clamber an incredible thirty some-odd feet up a palm tree to snip a coconut down for a snack. Most coconut crabs don’t bother to edge their way back down the tree trunk, and opt to just flop gracelessly onto the ground below, which doesn’t appear to harm them. Also, just a friendly reminder, getting hit with several pounds of falling coconut, or eight pounds of falling, giant fucking wanna-be monkey crab, can cause serious injury or death. While incredibly unlikely to ever happen, the coconut crab is, via aerial, kamikaze assault, theoretically the only crab on the planet that could (inadvertently) kill a human being.

All this being said, in reality, coconuts don’t make up the bulk of the coconut crab’s diet.

Its favorite food is….TV show hosts! Run Brian Cox! Run for your life!

Coconut crabs have a surprisingly varied diet. Much of their caloric intake comes from fallen and decaying fruit, but they also regularly seek out and indulge in carrion, as well as small reptiles, mammals, and even other crabs. Truthfully, if it’s stationary, or unwary enough to be captured…there’s a good chance that these guys are already on it. Their garbage disposal habits have made coconut crabs, to some, the potential reason why Amelia Earhart’s remains may have never been found; the idea being that if her plane went down over an isolated atoll, and she managed to survive long enough to make it to land only to die later, her body would have been consumed rapidly by coconut crabs. Some dubious records of a partial skeleton from the early 40s in Kiribati, along with other bits of evidence, have fed into the idea that this was Amelia’s final fate. But, it is far from settled, with much of the story’s claims of crabs carrying off and burying her bones like a pack of the weirdest dogs in the world not being supported by any behavioral evidence in these creatures.

As scary as coconut crabs are up close, in one-on-one combat, the worst they can inflict is a nasty, vice-like pinch. They, like every other crustacean in this list, is far more in danger of being boiled, broken, and buttered by humankind. Perhaps it is telling that even the largest, most physically imposing representatives of an entire taxonomic class are still outmatched by our species’ appetite, and that we have the ability to literally eat entire populations (or whole species) into oblivion. It would do us, and the world we inhabit, some good to be aware of this unbalanced power and privilege.

Image credits: Intro coconut crab image, Japanese spider crab, giant Tasmanian crab closeup, giant Tasmanian crab gif (clipped from this video from Eaglehawk Dive), giant Tasmanian crab with lighter (Paddy Ryan), man in cereal tub (Getty Images), coconut crab on forest floor, coconut crabs in trees, Man’s Conquest cover (George Gross)

© Jacob Buehler and “Shit You Didn’t Know About Biology”, 2012-2015. Unauthorized use and/or duplication of this material without express and written permission from this blog’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Jacob Buehler and “Shit You Didn’t Know About Biology” with appropriate and specific direction to the original content.


10 thoughts on “Claws: The Ultra-Jumbo Class of Crustaceans

    • Yes! I remember watching Mysterious Island when I was very young and thinking it was coolest thing. It didn’t matter that the effects were “bad” by 90s standards, as a little boy I was too enamored with super-awesome giant crab. Big fan of Jason and the Argonauts and the Valley of Gwangi too.

  1. I absolutely love arthropods Tom and I have no idea what were terrified of them… Nonetheless you wrote a pretty good article! Keep it up and More people should start to visit your blog!

  2. Awesome stuff man! As always your writing skills and knowledge are excellent haha.

    Also, idea for post. Shrikes/butcherbirds.

  3. Pingback: Morsels For The Mind – 04/09/2015 › Six Incredible Things Before Breakfast

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