Male Marsh Fiddler Crab (Uca pugnax); photo by FWC
Fiddler crabs (Uca sp.) can be spotted along the salt marsh shoreline at low tide and in mangrove swamps and sandy beaches, usually grouped in large numbers. Several species of fiddler crabs are found in Florida. They are called “fiddler” because the male holds one oversized claw, usually twice the size of their small claw, like a violin. Males use the claw to defend their territory and to attract mates. Both claws in the female are relatively small. Fiddler crabs are generally about 1.5 inches wide and have a square-shaped carapace (shell) usually brown to pale gray in color.
Marsh fiddler crabs live in burrows dug about a foot deep in the mud and sand close to the water’s edge. As the tide comes in or when alarmed, the crabs retreat into the burrows. Hundreds of these tiny creatures can be seen moving in mass making faint clicking sounds as they flee back into their burrows. The opening is plugged to keep out the water.
Besides the multitude of small holes along the shoreline, fiddler crabs litter their habitat with little mud balls, created while feeding. Fiddler crabs use their small claws to pick up tiny amounts of sediment. After taking a mouthful of mud, fiddlers use specialized mouthparts to scrape food materials (algae and decaying plant and animal matter) from the sediment then spit out anything inedible in a compact mud ball or “feeding pellet.”
Though not rare or endangered, fiddler crabs play a significant role in many marsh processes and the coastal food chain. Their burrowing creates a maze of tunnels that aerate (add oxygen to) the marsh. This consequently enhances the growth of grasses like saltmarsh cordgrass, helping to preserve the coastal wetland community. They stimulate the turnover of important nutrients by breaking down organic matter. Fiddler crabs are also a valuable food source to a variety of predators, including fish, herons, raccoons, and foxes. They are good environmental indicators and sensitive to environmental contaminants. Fiddler crab population densities are an example of the high productivity of our vital wetlands.
The next time you visit North Peninsula State Park, stop along the edge of the marsh and quietly approach the many fiddler crabs you will see there. If they do not notice your presence, you will enjoy watching them until they get spooked and make a mad dash into their burrows.
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