Uca perplexa is a species of fiddler crab. It is found from the Ryukyu Islands, Japan to India, throughout the Malay Archipelago, along eastern Australian coasts from Queensland to New South Wales, and in various Pacific islands, including Fiji, Tonga and Vanuatu. As in other fiddler crabs, the male has a greatly enlarged claw, which is used for signalling. The higher the claw is waved by the male, the greater his chance of attracting a female; the size of the claw is therefore subject to sexual selection.