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Fiddling while my wife burns

July 19, 2010

When my wife and I go to the beach we have a system in place.  She gets to lay around on the sand and read her book and take in the peaceful surroundings while I, who thinks laying around doing nothing but reading a book when there are saltmarshes to explore sounds like the most boring things ever, get to haul my scope up around the other side of the island to look for birds and cool stuff.  So once the various accoutrement of beach-going are unloaded and set up, the chairs, the cooler, the towels, etc, I’m free to roam.  So roam I do.

By the time the day wore into afternoon, the birds were slowing down and the tide was coming in.  Men with nets were starting to wade into the area behind the marked waterbird nesting area where I’d been set up, and what birds that were there, mostly Wilson’s Plovers and Willets, had split for higher ground as the sand flats they had been foraging in slowly disappeared beneath the advancing water.  All the people walking around were really cramping my birding so I tried to find a more secluded spot, ending up down by the end of the marsh where there were no birds beyond the omnipresent Boat-tailed Grackles, but hundred of Fiddler Crab burrows whose occupants where busy grazing on the mud, fighting amongst each other and generally doing the things that Fiddler Crabs do.

In my subsequent attempts to identify them to species, I ran into the dilemma nearly all would-be invertebrate identifiers are familiar with.  There is no singular “Fiddler Crab”, there are about 100 species of Fiddler Crabs in the genus Uca distributed around the world which all look essentially identically large clawed and spindly and are only differentiated by things like oblique ridges of small granules on the inner surface of the larger claw extending from the lower margin to the wrist cavity.  And here I though Empids were tough.

Fortunately my focused googling turned up a really useful document (.pdf) from the South Carolina Department of Natural Resources on Fiddler Crab identification.  Turns out the East coast of the United States is home to three species of Fiddler Crabs, only two of which are found in salt-marshes (the other prefers freshwater marshes).   So my crabs in question were either Atlantic Mud Fiddler Crabs (Uca pugnax) or Sand Fiddler Crabs (Uca pugilator).  By virtue of their leg color (dark), I determined them to must likely be the Mud Fiddlers, though according to the document both Mud and Sand Fiddlers can be found together in the same place so it’s quite possible both were present and a few of the crabs seemed to have paler legs than others.  Who knows?  Perhaps I should have been paying closer attention at the time.

In any case, the crabs were busy waging their tiny battles against each other for control of their burrows, waving their claws at each other to determine who had the largest and when that didn’t work, pushing against one another like tiny five appendaged sumo wrestlers.   When I’d walk by they quickly scurry into their designated burrow only to re-emerge and continue where they had left off when I had repaired to a suitably far distance, which often happened to be right smack in the middle of a different crowd of Fiddler Crabs.  However, I determined that by training by scope on the mud instead of at the horizon, I was able to get up close and personal without causing the whole crab nation to run for their burrow immediately.  It also allowed me to snap a few photos through the scope.

When I was about 7 or 8 years old, I convinced my parents to get me some Fiddler Crabs I’d seen at a pet store in the mall.  I took them home and proceeded to create what I thought was a realistic environment for them in a 10 gallon aquarium, complete with water pool and sand berm.  I have to say it was pretty cool, and I had imagined that the Crabs would do their crab thing scurrying along the water’s edge after bits of official Fiddler Crab food I would judiciously scatter thereabouts.  It turns out the habitat was a bit too naturalistic, because the first thing my pet crabs did was to construct burrows for each crab and spend 23.5 of every 24 hours in those burrows.  The 30 minutes they’d spend out of the sand was usually around 3:00 am, or so I figured, since the crab food was gone the next morning.  The moral of this story is that Fiddler Crabs make awful pets.

They are, however, pretty cool to watch in their regular environs and make even the slowest of beach afternoons a pleasant experience even if the birds are less than spectacular.

  1. July 20, 2010 8:00 am

    Nice post on a topic I don’t know anything about. On your next to the last picture, I can see that one crab seems to be right handed (should I say right clawed?) and the other one left handed. Did it seem to be roughly a 50%/50% distribution between the two types?

  2. Nate permalink*
    July 20, 2010 10:26 pm

    @Laurent- Good eye! I didn’t notice it at the time, but everything I’ve read subsequently suggests that there is a 50/50 distribution in handedness (clawedness?).

    Apparently it doesn’t matter to the crabs, but it’s thought that there is some effect on the male displays in that when the crabs are different-handed it’s easier to compare the size of the claw, and when they’re the same handed, it’s easier to link claws and do battle. Interesting stuff.

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