(BG) Atlantic Marsh Fiddler Crab (Uca pugnax) has the requisite royal blue spot between the eyestalks on a paler blue background
2014-8-15 Bombay Hook NWR, DE
resource for Fiddler Crabs:
http://www.fiddlercrab.info/u_pugnax.html
info
http://bugguide.net/node/view/361847
and
http://bugguide.net/node/view/1007876/bgimage