The Fiddler Crab

Going to the ocean's edge is always an opportunity to check out those who share the beach with us. There's people watching, of course, one of the all-time great beach pastimes, but a more closely focused look will reveal the most interesting and amusing of our waterfront denizens, the fiddler crab.

Fiddlers are one of the most conspicuous inhabitants of the intertidal zone, that band of sand and mud between the high and low tide lines. Ranging from Massachusetts south to Florida, they live wherever the ground is stable enough for them to dig their burrows-marshy areas are ideal-and can be seen foraging for food in large groups when the tide is out. These little creatures are fast and shy-approach a group and it will react by scuttling away en masse, or instantly disappearing down the ¾-inch-wide holes that mark their individual homes. Wait and watch a bit, though, and they'll reappear, having apparently forgotten the threat that so terrified them a few seconds earlier.

This is the Atlantic Marsh Fiddler Crab. Its scientific name, Uca Pugnax, implies a pugnacious nature, largely because of the behavior and appearance of the males. While female fiddlers have two small claws, used for feeding, the males have one small claw and one extremely large one. The male fiddler crab waves this claw up and down, looking like he's playing the fiddle, to challenge and intimidate other males, wrestle with them claw to claw and invite females to mate. The wrestling seldom causes any damage to either party. The large claw is useless for gathering food, so the male has to work twice as hard as the females with his small claw to keep fed.

Fiddlers eat by collecting bits of mud with their small claws and sifting through the mud for the detritus of decaying plant and animal matter. They pick up the mud, bring it to their mouth, and scrape out the nutrient material, then deposit the mud and sand granules back on the beach in a series of little round pellets. They're scavengers, not carnivores, and as such play an important role in recycling the tiny algae and bits of dead sealife that accumulate on the shore.

They also leave larger balls of sand to mark the spots where they've excavated their burrows. These are cylindrical tubes up to two feet long, painstakingly dug and regarded as territory to be defended, although in an emergency a crab will bolt into any handy hole, not worrying about the fine points of ownership. These dwellings provide protection from enemies, of course, like seabirds, raccoons or other shore life, but also from the sun and the danger of drying out.

Because these holes are below the high tide mark, they are submerged twice a day. While the fiddlers have gills, they actually need air to breathe, not water, and so when they go to their underground homes as the flooding tide approaches, they plug up the tunnel behind them with a ball of sand, trapping an air pocket that will last them until the ebbing tide opens the beach to them once again. In the winter they enter the burrows and hibernate there, emerging again the following spring to eat and mate. They usually have a lifespan of about a year and a half if they can avoid being eaten by their enemies. During that time they molt (shed their shell) periodically in order to grow, and while waiting for the new shell to harden they hide in the burrow.

Because of their small size, fiddlers aren't consumed by humans-even the large male claw wouldn't yield enough of a speck of meat to be worth consuming-but they are an important part of the coastal food chain. Herons, egrets and blue crabs all find them tasty, and some fisherman use them for bait, confirming their attractiveness to fish as well. The biggest threat from humans comes from encroachments on their environment, like overdevelopment of beach and marshy areas.

If you'd like to take a closer look at a fiddler crab, just pick one up (gently) in a cupped hand. They're very fast and will try to skitter away, but will eventually stand still long enough for a good look. Don't worry about the big claws on the male; you're in no danger. After looking at the claws, notice the eyes perched atop long, thin stalks, giving them the ability to detect approaching threats that loom above their visual horizon. Incidentally, if you walk toward them, you're a threat, but if you're willing to lie down on the flats and keep still, you'll become a part of the background and can watch them feed right before your eyes...until you move and send them into panicked retreat.

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