Species identification can be difficult. If you are obsessed with taxonomy, expect to have a rough time. Most fiddlers sold in the US come from their native habitat in Florida. Recently, imported species are becoming increasingly available, from countries such as Indonesia. Ask your pet store where their crabs come from, or what their supplier is. A common Florida species is Uca minax, the red jointed fiddler. It can be identified by its trademark red joints. The joints where the top claw meets the bottom, and where the claw meets the arm, as well as several other points, will have a slight red or pink hue. The claw will usually be gold or brown on top, and white on the bottom, with the rest of the body having a tan or brown coloration. Colors may vary, however, and identification can be difficult. Two other common species in Florida are Uca pugnax, and Uca pugilator, along with several other species and subspecies. Research online, books, and published scientific works may help you identify your species.
Known as the red-jointed fiddler, this species tolerates the lowest salinity among the species found in the United States. Its geographical range extends from Massachusetts to Florida, and from Florida to Texas. This species is one of the most commons sold in pet stores in the US. They can survive short periods of immersion in freshwater, but not indefinitely. The prefer lower salinity than other US species, and the ideal salinity ranges from 1.005 to 1.010. Uca minax can be easily identified by its trademark red joints. In the wild, they are mud dwelling crabs.
Notice the red joints: