Many species of fiddler crabs, Uca sp., are found in all colors around the world but only one is native to North America, Uca pugilator, the sand fiddler crab.
The common name “fiddler crab” appears to have originated among the English-speaking residents of the British colonies that eventually became the United States. Male fiddlers have one very large claw used in mating displays and a smaller one that is used for feeding. The name derives from the constant movement of the small claw across the large claw when feeding, which is similar to a bow being drawn across a violin.
A fiddler crab, sometimes known as a calling crab, may be any of approximately 101 species of semi-terrestrial marine crabs. Fiddler crabs are most closely related to the ghost crabs. This entire group is composed of small crabs, the largest being slightly over two inches across. Fiddlers are found along beaches and brackish inter-tidal mud flats, lagoons and swamps.
Like all crabs, fiddler crabs shed their shells as they grow. If they have lost legs or claws, a new one will be produced when they molt. If the large fiddle claw is lost, the small one on the opposite side will begin to grow and a new small claw will appear where the large one was lost during molting. Newly molted crabs are very vulnerable because of their soft shells and hide until the new shell hardens.
Fiddler crabs communicate by gesturing with their claws. The males’ large claw is also used in ritual combat during mating.
Some experts believe that the feeding habits and burrowing of fiddler crabs play a vital role in the preservation of wetland environments by aerating the soil.
Fiddler crabs live no more than two years in the wild and up to three in captivity.
The fiddler crabs found in pet stores need some salt in their water as well as access to air and dry land.
Fiddler crabs do well at a range of temperatures between about 75-85 F.
In the wild fiddler crabs are scavengers, eating bits of organic matter they find in the sand or mud. In captivity, they can be fed sinking crab food, fish food meant for scavengers (sinking tablets, shrimp pellets, etc), and freeze dried plankton and shrimp.
Signs of health in fiddler crabs include growth and regular molting. Once a crab molts, their previous exoskeleton will likely be whole in the tank, looking eerily like a ghost. It is a good idea to leave the exoskeleton in the tank, at least for a week or so. Often the crabs will ingest part of the shed exoskeleton, and it serves as an excellent source of calcium, which they need to produce their new shell.