Halloween Moon Crab
Hartnollius quadratus
The Halloween moon crab is a colorful land crab from the Pacific coast of Mexico to Panama. Long sold as Gecarcinus quadratus, it was moved in 2025 to a new genus as Hartnollius quadratus. Both sexes are purplish, red and white with colored spots, with intense purple claws and yellow or orange legs, and museum specimens reach about 6.4 cm across the shell. In the wild it burrows in coastal forest within a few hundred meters of the sea, at up to six crabs per square meter in Costa Rica, and its appetite for seedlings shapes which plants grow there.
Like other land crabs, females must release their larvae into the sea, where they drift before returning to land, so breeding it in captivity means raising larvae in seawater. When disturbed in its burrow it makes a rasping sound by rubbing a claw against ridges on its shell. Keepers report that tankmates may kill a crab while it molts, and they offer a deep, moist substrate with fresh and brackish water dishes. It is not covered by CITES or the US endangered species list, and USDA asks buyers of land invertebrates to check with its permit office before buying.
Colors: Purple with Orange Spots
