Crabs
Soldier crab / Mictyris brevidactylus / Minami kometsuki-gani / ミナミコメツキガニ
This small crab (1 to 2 centimeters) gets its name from its habit of moving around the muddy beach side of mangroves at low tide in large groups, as if in military formation. The species on Amami-Oshima is endemic to the Ryukyu Islands. The crab’s body turns bright blue in the winter, with tan legs and claws. It feeds by sorting through the sand in search of plankton and other organic matter, which it strains in its mouth, leaving small pellets of sand behind. Unlike many crabs, soldier crabs walk forward, not sideways. When disturbed, they have the ability to quickly disappear by digging into the sand with a twisting, corkscrew motion. They also do this when the tide rises, and stay buried until it ebbs. These crabs have a number of predators: herons, plovers, fish, and larger crabs.
Okinawa fiddler crab / Uca Austruca perplexa / Okinawa hakusen shio-maneki / オキナワハクセンシオマネキ
The Okinawa fiddler crab, one of seven species of fiddler crab on Amami-Oshima, is found on sandy mangrove mudflats. Its body is about 2 centimeters wide, with color variations of black, white, and blue. The males have one conspicuously larger claw—either right or left—which they wave around to attract females or fight off other males. The crab eats by filtering sand with its mouth for bits of plankton or plants and other organic matter. It is very cautious, and quickly hides in a burrow when it feels threatened. The fiddler crab gets its English name from its big claw’s resemblance to a violin; the hakusen, or “white fan,” of the Japanese name refers to the crab’s mating behavior, which resembles a fan being waved.
