Salt Marsh Part 3: Mr. and Mrs. Crab

(Read part 1 here and part 2 here.)

Walk through the marsh on a cool day, look closely at the surface of the salt pan, and you’ll notice that it’s riddled with small round holes.

These are the burrows of fiddler crabs (Uca sp.).  The little balls of sand surrounding them have significance as well – they’re the results of the crabs’ excavation efforts.  In some places you can see two distinct size classes of sand balls, big and little.  My understanding is that the big ones are from crabs digging their burrows, and the little ones are from their feeding activity.  They get a mouthful of sand, swish it around to extract the tasty microbes, detritus, etc., and spit the sand back out as a compact ball.

Come back on a warmer day and you’ll find the marsh crawling with the crabs themselves.  If you move fast, it’s fairly easy to pin them and pick them up.

This is a female – you can tell by her two tiny claws.  She’s on the small side, they get bigger than this.  Actually there are several different species of fiddler crab of different sizes and colors found in our marsh, but I’m not an expert at distinguishing them from each other.

This is a male.  Full disclosure: he’s dead.  On the day I took my camera with me to the marsh, I had a surprisingly hard time finding and catching a decent-sized live male, so when I found this dead one at the edge of a salt pan I picked him up and snapped some photos of him instead.  Obviously the big difference between him and the female is his one big claw, the main purpose of which is communication.  The males wave their big claws back and forth as a display to attract females (you should hear fifth graders giggle when I wave my arm back and forth in the air and tell them it’s fiddler crab for “heeyyyyy ladies!”).  If the big claw is broken off, the remaining little claw grows into a big one and a little one grows back in place of the big one that was lost.  Mammals are pretty much the only group of animals without any significant ability to regrow lost limbs.  Hardly seems fair, does it?

Hope you’ve enjoyed my guided tour of the salt marsh and its little critters.  It’s also full of ibises, storks, spoonbills, herons, and egrets, of course, but birds are a lot harder to photograph with my point-and-shoot camera.  One of these days I need to learn how to use an SLR…

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5 thoughts on “Salt Marsh Part 3: Mr. and Mrs. Crab”

  1. Thanks for Part 3! I saw the fiddler crab species with the large red claw on Cumberland. Three of us were walking along the boardwalk over the mud flat, and the crabs all disappeared into their holes. My friends walked on, and the crabs came out – perhaps they felt the vibrations of feet receding and thought the coast was clear. They all came out and proceeded to wave their single red claws madly.

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