What Crabs Are The Fightiest?

Grab the children and run for the hills! Coconut crab on a stick. Photo from Wikimedia Commons

So a good friend of mine asked this weekend on Facebook what kind of crabs are the fightiest. Great question! First, for the sake of argument let us assume we’re not talking about the kind of crabs you catch on a bachelor party gone wrong in Atlantic City after multiple Maker’s shots followed by tequila chasers. Those crabs are actually the insect Pthirus pubis, a type of lice that infects the pubic region. And of course those lil’ bastards are fighty.

No the crabs I will discuss here, while also Arthropods, are in a completely different subphylum, Crustacea as opposed to Hexapoda. True crabs are in the order Decapoda (Class Malacostraca), or Order SuperTasty as I like to refer to it, with the lobsters and shrimps, but form their own group (infraorder Brachyura). I will assume the crabs we are speaking of are Brachyurans.

To address what crabs are the fightiest, I will assume the question actually is:

If the shit goes down, which crab do I want to have my back? or What crabs are bad ass mothers? or Who would win a crab fight club?

That’s one big ass crab

Holy Jesus! Japanese Spider Crab from Popular Science Magazine, jun. 1920 and Wikimedia Commons

Let’s face it. Size in the animal kingdom is important in a throwdown. In a study of fiddler crabs, intruders were more likely to win a fight against a resident male crab if they were larger. In addition, fights won by larger males took much less time than those by smaller males. Likewise, in swimming crabs fights are usually won by the larger male. Even among female velvet crabs, larger is better. And in those scurrying little ghost crabs, big males are able to defeat smaller males in contests over burrows.

So the choice then might be for the Crabzilla of Brachyurans. A title held by the Japanese spider crab, at over 40 pounds and ranging 12 feet from the tip of claw to claw. However, given these big bastards live in deeper cold waters of Japan and are known to be long lived, 100 years+, they are likely to have slower metabolic rates, i.e. be wee bit sluggish. Being old and slow is not exactly the best traits in a street brawl.

For shear scare-the-hell-out-of-your-opponent-psychological-mind-game-before-the-fight-begins tactic, the coconut crab is a winner. See this bad boy come your way and most will turn tail. The coconut crab, Birgus latro, is a species of terrestrial hermit crab and is the largest terrestrial arthropod in the world. Handy if the brawl is out of water. The coconut crab weighs in at whopping 9 pounds and is little over a foot long. Compared to the rather puny claws of the Japanese spider crab, coconut crab claws are robust and can easily cause pain. It is said that they will also be unlikely to release a claw grip once clasped down.

It Is Not How Big You Are, But the Size of the Stick You Carry

Claws of Death on the Blue crab. Photo from Wikimedia Commons

Size isn’t everything. Sometime you just need to carry a big stick. In shore crabs, claw size, not overall body size, was a more reliable predictor of a fight’s winner. Indeed, hermit crabs rely upon claw displays and presentations to assess crab opponents. So let’s contemplate the crab claw beyond just butter. After an unfortunate incident with my pinky on a Gulf shore, Florida stone crabs (see pic here) seems like a contender for our fightiest crab. Stone crabs have one claw called the “crusher claw” and the other one called the “pincer claw”. Stone crabs feed upon mollusks aided by the crushing claw that can generate up to 19,000 pounds per square inch. For a frame a reference, a car crusher only needs about 2,500-3000 pounds per square inch. Once the mollusk shell is crushed the pincer claw is used to cut or tear shell and tissue. Crushing and tearing seem handy in a fight.

For shear sharpness of a the claw, the damn-near-a-knife-like-edge claw of the blue crab is also contender. There seems to be a consensus among marine biologists and our fingers that this is the case anyway.

But What Crab Really Wants and Enjoys a Fight?

Trapezia tigrina English: Red Spotted Guard Crab from Steve Childs from Lancaster, UK

In a 1987 paper in the Journal of Crustacean Biology (yes there is a journal dedicated to crustacean biology), Michael Huber states “Aggressive bouts typically began with a period of display which was almost invariably followed by violent fighting. Aggressive displays resembled those of other crab species, but fights were longer and more frequent, and injuries more common, than in other crabs.” So why are the crabs Huber speaks of so agressive? The genus Trapezia contains the crabs that live in association with, feed upon, and hopelessly reliant upon corals. Each coral crab individual must simultaneously defend the corals against other predators, like starfish, and other coral crabs. Thus intense territorial agression, kind of like your short-statured, Chihuahua-esque friend with a Napoleon complex always picking drunk fights with the biggest guy at the bar.

Of Course There is Doping

Crabs that have greater fighting ability also have higher concentrations of dopamine, octopamine, and serotonin in their systems. So maybe we just need to find a crab that juices. And what ever you do don’t feed a crab, crab fights last longer and crabs get angrier when hungry. Or possibly make sure the crab is infected with parasites, as “the likelihood of a male crab winning a ritualized fight against a conspecific in the field was associated with its infection level.”

Dr. M (1629 Posts)

Craig McClain is the Assistant Director of Science for the National Evolutionary Synthesis Center, created to facilitate research to address fundamental questions in evolutionary science. He has conducted deep-sea research for 11 years and published over 40 papers in the area. He has participated in dozens of expeditions taking him to the Antarctic and the most remote regions of the Pacific and Atlantic. Craig’s research focuses mainly on marine systems and particularly the biology of body size, biodiversity, and energy flow. He focuses often on deep-sea systems as a natural test of the consequences of energy limitation on biological systems. He is the author and chief editor of Deep-Sea News, a popular deep-sea themed blog, rated the number one ocean blog on the web and winner of numerous awards. Craig’s popular writing has been featured in Cosmos, Science Illustrated, American Scientist, Wired, Mental Floss, and the Open Lab: The Best Science Writing on the Web.





9 comments on “What Crabs Are The Fightiest?
  1. I will go with the blue crabs – I had some “pet” ones that were always ready to put up a fight, let alone those in the wild.

  2. Of all the meanest, dirties, most low-down good for nothing bastards, with mule-headed disposition, ain’t nothing comes close to the Blue Crab, the meanest SOB in the Sea.

    And coconut crabs are anomurans there, pardner.

  3. You need to consider some factors. While some crabs have amazing crushing power, they are so slow to close their claws that anything which would actually be in a fight with it would have plenty of time to actually move out of the way. Also, personality can vary a lot among species. For example, three species of fiddler crab found sympatrically in Panama are Uca terpsichores, Uca beebei, and Uca stenodactylus. All three are about the same size, live in the same place, and have major claws which are pretty similar in shape. However, if you pick up a bunch of them, only U. stenodactylus is likely to hurt you with a strong pinch. It’s simply a much more aggressive species than the other two. If you put 10 of each into a small container to take back to the lab, U. terpsichores and U. beebei will largely come back whole, while the U. stenodactylus will have torn into each other with most missing limbs.

    You simply gotta go beyond the morphology and consider the psychology of the crabs. Should be a new discipline: Cancychology.

    • Great point! It was unfortunate I didn’t find a lot of literature discussing this other than Huber’s paper on coral crabs

  4. The worst pinch I’ve experienced was from a Lady crab, which caused me to use some unladylike words.

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