Ucides cordatus

Ucides cordatus, the swamp ghost crab, is a mangrove crab native to the western Atlantic coast, recorded from Florida in the north to Uruguay in the south, and known in Portuguese as caranguejo-ucá. It is one of two species in the genus Ucides. The two claws differ in job: the left one is sharp and used to cut and feed, while the larger right one crushes. Males and females look different, the females being larger and bulbous-backed with a dull dark green and purple carapace, and the males flatter with a pale blue centre on a beige back. The crab lives mostly on land in mangrove forests, digging burrows at the base of trees that can reach about 1.6 metres deep and that help mix oxygen into mangrove sediment. It eats chiefly mangrove leaves, bark and roots, and young crabs feed on worms and microorganisms in the sediment. Each year in the breeding season it walks to the coast to mate and release eggs, a mass migration called a andada in Brazil, where the species is harvested for food and has seen its population fall since 1988.