Fiddler Crabs

FINCA TATIN, Guatemala- “Why do these crabs only have one claw,” a visitor to the Finca Tatin asked me.

“Because that is how God made them,” I spoke with firm finality as I walked by.

How else could I respond?

Though, I must admit, another answer could have been, “Because the lady crabs like them that way.”

The girl was talking about the thousands of Fiddler Crabs that cover the ground surface of the swampy area of the finca that serves as the transition between the river and the forest. These crabs move through the muck with purpose throughout the day — eating, fighting, and showing each other how tough they are (to impress the ladies, of course). The males of the species seem to display the same priority sets as males from most other animal species: they sit around with other males comparing claw size. They think the lady crabs like the big ones. Evolution has proved them correct.

Fiddler Crabs actually have two claws, but you only notice the really big one which the males grow vastly out of proportion to the rest of their body. The female crabs just have two little claws, and nobody really notices them as much. But this is not to diminish the role of the females, because they are primarily responsible for creating one of great freaks of nature: their male counterparts.

The male Fiddler Crab is a vastly unsymmetrical little beastie, as it possess a horridly overgrown limb that hovers in front of its face as inconspicuous as a white man in Harlem. In a rough estimate, I would say that the length of the claw in question is nearly the width of the entire crab and its breadth is about the same as the measurement from the bottom to the top of the organism. In point, the male Fiddler Crab can almost completely hide behind this claw if viewed from the front.

Against things his size, there is no penetrating his fortress — he is all claw.

The name Fiddler Crab is the result of someone else’s observation that the males look as if they are playing a fiddle as they draw up food with their small claw and pass it behind the large one to their mouth. I have been watching Fiddler Crabs for a month and a half, and I have yet to see them do anything that even roughly looks like someone playing a fiddle. Perhaps this is just a matter of perception.

But regardless of whether or not the large claw resembles a fiddle, it can be regrown if severed or otherwise lost. The small claw on the other arm will compensate for the loss, and it will grow into a big claw the next time the crab sheds its shell. New legs can be sprouted too during the molting periods.

It is probably a good thing that these crabs can regrow their freakish appendages, as the male’s seem awful proud of their large claw. They can often be seen waving these big claws in the air or pounding them on the ground throughout the day — sometimes it appears as if they are trying to intimidate other crabs, sometimes it seems as if they are trying to communicate intentions that are no more subtle:

Sometimes, 10 to 15 males will gather in a group and slowly and rhythmically wave their giant claws over their heads, like hippies dancing at some music festival. I watch the crabs dancing, but, like many other dancers, they are actually trying to attract mates. They seem to think the lady crabs like the big ones, so the males put on a show to prove to all the ladies who has the largest claw. I watch the show, it seems to go on indefinitely, but I don’t notice any female crabs demonstrating any abject sign of attention — they all seem to be elsewhere in the swamp, gathering food, eating, not showing much interest in the males battling out their egos. But, apparently, the females really must like the big ones — as these males would not have been granted with such great, appalling, inproportionally huge appendages if it were otherwise.

Deference is given to the Fiddler Crab with the largest claw, mating preference often seeks out the most extreme variations of some chosen features. The large claw on the male crabs are meant to act as a defensive appendage — the bigger the claw the more it can be use to chomp other crabs. I am unsure of how territorial these crabs are, as they completely cover the ground surfaces of the swamp — you can see over a hundred in a single glance — but from only a brief observation it is obvious that they use these claws against each other aggressively and frequently.

Video of Fiddler Crab mating ritual

The crab with the largest claw gets what it wants, the crabs whose claws have been proven smaller scatter quickly away.

Hierarchy structures, mating structures, are often based around visual cues. Perhaps this is an ingrained instinct to curb species from doing actual physical damage to themselves during status rights. There are physical cues that indicate strength, you defer to those who possess them to a higher degree than yourself. You do not want to risk getting chomped each time you run into another crab, so you make sure you know whose claws are bigger than your own — you look at them and either chomp or run. Likewise, the projected valor of a potential mate often comes from looking at him.

I watch the Fiddler Crabs in a swamp in the jungle of the eastern fringes of Guatemala. Two males approach each other. One raises his claw, the other answers the call. They take turns lifting up their claws while watching the potential foe do the same. They take a couple scutter steps forward, a couple backwards, soon one begins moving more backward than forward — it retreats.

The crab with the largest claw wins.

We all play the same game.