FIDDLING AROUND AT THE SHORE
by Anita Rafael
Not far from Newport, Rhode Island, in the electronic research labs at the Massachusetts Institute of Technology in Cambridge, serious scientists are spending their summer building robotic fiddler crabs. The purpose of this undoubtedly expensive and ultra-high tech project is to make a teleoperated ten-legged Uca puglax, which they say will help us (the non-geniuses of the world) better comprehend what these fascinating little creatures are all about. Nice try, guys, but we’d prefer to be hanging out at the beach this July rather than indoors at your lab. Luckily, you don’t have to be a scientist to be a fiddler crab spotter. Look for them munching algae and organic debris in tidal puddles along the shoreline. They are everywhere where there is brackish water and marsh like conditions – all around Narragansett Bay, Fiddlers, however, are not a true aquatic species because they breathe air, not water, through their gills. Also known as mud fiddlers, they dig foot-deep burrows, and, when the tide rises, they plug up their hiding places with a balls of mud and breathe the air they have trapped inside. Sometimes their burrows are interconnected deep below the sand. As the tide recedes, the crabs come out to forage and feed again. They are active most of the day, which makes them fun to watch, and because they are so abundant, they are easy to find. Fiddlers are brownish, with the front of the shell and eyestalks ranging from blue to turquoise. The large claw of the male is usually yellowish-orange to yellowish-white, sometimes in a speckled or marbleized pattern. There are about 100 species and sub-species of Uca, first-cousin to the common ghost crab, and they have many interesting names around the globe. In Barbados, they are known as fever crabs; in Japan, siho maneki, which loosely translates "beckoning for the return of the tide.” Jamaicans call them deaf ear crabs because of a belief that crushing a live crab and pouring the juice into your ear could cure deafness and earache. (Not our best medical advice – go see a doctor.) Now, about that fiddle, or as taxonomists call it, the cheliped. What looks like a gross deformity in the male of this 2-inch crustacean, its giant claw that is sometimes 20 times the size of its walking legs, is actually its best defense against predators, not to mention nosy lab researchers. The “fiddle” is the major claw, and as the creature eats using its less cumbersome minor claw, the back and forth motion makes it look like it is using a violinist’s bow. (You can get a better idea of this effect when you are looking at them straight on at crab eye level.) The more symmetrical females lack the big claw and have two small claws, which makes it easier and more efficient for them to feed. Like us, fiddlers are either left- or right-handed, and it is this large claw that is the most important part of the crab dating game. It’s a guy thing – the males line up side-by-side outside their entrances, and, to impress the females, they wave their big appendages at them. On occasion, there are too many males in a colony vying for one mate and they violently arm-wrestle over who gets the girl. When a she-crab likes what she sees, and presumably size matters because females have been observed to be pretty picky about who they go to burrow with, she gets a deep-stare, eye-contact thing going with him. Then, she follows him into his tunnel for about two weeks of private time before she emerges with her incubated eggs. Both genders hide during the semi-annual molting of their shell, and understandably, with absolutely nothing to wear, you would stay inside, too. Everything fiddler crabs do – foraging, eating, molting, tunneling, hiding, mating, and fighting – is part of the big picture of the ecosystem of Narragansett Bay. They clean up the detritus from plants, and their burrows aerate the terrain around marsh grasses, and thus support the growth of vegetation. Of course, fiddlers are part of the food chain – tasty morsels for many large predators, including blue crabs, waterbirds such as egrets and herons, and small mammals such as raccoons. The crab’s worst threat is people, no surprise here, who carelessly pollute the water. While there is no commercial fishing of fiddler crabs, aquarium stores sell teeny tiny ones as house pets. However, crustaceans in general are fairly low on the list of wild things you’d like to cuddle with and, besides, they have a minimal life expectancy in captivity. Instead, get outdoors and spend a little time at the shore spying on the busy little fellows, and while you’re enjoying the sunshine and the fresh air and your new arthropod friends, have a little sympathy for those mechanism-minded inventors back in the M.I.T. lab working to assemble their scale model robo-crab. Seriously, have you ever heard of anyone who needs any sci-fi help to fiddle away a day at the beach?
