Fiddler Crab
Uca pugnax

f10 @ 1/2000s, ISO:2500, Nikon D300 w 300mm

"Uca pugnax," Wikipedia, the free encyclopedia. Uca pugnax, commonly known as the Atlantic marsh fiddler crab, is a species of fiddler crab that lives on north-western shores of the Atlantic Ocean. Uca pugnax is the most common species of fiddler crab on the east coast of the United States. Its natural range extends from Cape Cod to northern Florida. In 2014, its northern limit was extended to Hampton, New Hampshire, as a result of a range expansion possibly due to climate change. There is noticeable sexual dimorphism in Uca pugnax. Although both males and females are olive-brown in color, males have a carapace width of 1523 mm (0.590.91 in), and a patch of royal blue on the carapace, while females lack the blue patch and are only 1318 mm (0.510.71 in) across the carapace. In both sexes, the pereiopods (walking legs) have dark bands, and the eyestalks are narrow. The most conspicuous difference is the form of the chelipeds (claw-bearing legs); in females, they are similar, while in males, one is greatly enlarged and colored yellow.
Herring Brook Marsh, West Falmouth, Massachusetts