Fiddler crab

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A calling crab, also known as a fiddler crab, is any of around 100 semi-terrestrial marine crab species that make up the Uca genus. As members of the family Ocypodidae, fiddler crabs are closely related to ghost crabs in the Ocypode genus. This entire group consists of small crabs - the largest being slightly over two inches wide. Fiddler crabs can be found along sea beaches and brackish inter-tidal mud flats, lagoons, and swamps. Fiddler crabs are most well-known for their sexually dimorphic claws; males' major claws are significantly larger than females', who have identical-sized claws. Like all crabs, fiddler crabs shed their shells as they grow. If they lose legs or claws during a growth cycle, new ones will be present after molting. Males with lost large fiddle claws develop one on the opposite side following their next molt. Newly molted crabs are extremely vulnerable due to soft shells and tend to hide until new shells harden. Fiddler crabs exhibit constant circadian rhythms in controlled laboratory settings that mimic tidal ebbs and flows. Crabs turn dark during daylight hours and light at night.