Atlantic Marsh Fiddler Crab (Uca Pugnax)
WHY ARE THEY CALLED FIDDLER CRABS?Adult male fiddler crabs have one large front claw and one small one, while females and young fiddlers have two small claws. The large claw looks a bit like a fiddle. The male fiddler crab waves this claw and wrestles other males to mark his territory and attract mates. The small claws are used for gathering food. Fiddlers usually live in large groups, which helps them to spot predators (dangerous animals) more easily. (In the photo, the male is above, the female below.)
To see how a fiddler crab moves, click on the projector!
WHERE DO FIDDLERS LIVE? The Atlantic Marsh Fiddler lives near water in the mud or sand. They dig burrows (underground tunnels) that are 1/2 inch wide and go almost straight down in the mud. The burrows can reach a foot deep. They may hook up with other tunnels and have more than one entrance. These burrows provide a quick escape from predators like fish, raccoons, and water birds. Most fiddlers look for food at low tide and stay near their burrows. If they are too far away when danger comes, they will jump into any burrow to escape. Burrows also offer a cool shady place for fiddlers to get away from the sun. Finally, burrows provide a place for the crabs to stay during high tide. Fiddlers roll up a ball of mud and use it to plug the hole of their burrow during high tide. When the water covers their burrow, a tiny pocket of air is trapped inside for them to breath. All crabs have gills, but crabs that live on land, like the fiddlers, breathe air instead of water. Their gills must stay wet to work, so they must stay near water at all times.
HOW DO FIDDLERS COMMUNICATE? Claw-waving challenges other males to fight and invites females to mate. The fighting is rarely ever dangerous, like an arm-wrestling contest. Both arm-wrestlers get to show their strength to the opposite gender without any serious danger to themselves. Some crabs are right-handed and some left-handed.
WHAT IS MOLTING? Because theres no space to grow inside a hard shell, molting is the only way the fiddler can grow. The fiddler molts (or reabsorbs) its shell and grows a new larger one. Most of these so-called soft-shelled crabs stay hidden inside their burrows because they are weak and have no shell to protect them. Adult fiddlers will molt one or two times each year.
WHAT DO THEY EAT? Fiddler crabs feed by collecting bits of mud with their small claws and sifting through the mud for detritus. Detritus is decaying (rotting) plant and animal matter. This is released into the water from marsh plants and animals that have died. This decaying matter is full of the nutrients those plants and animals stored while they were alive. Eating detritus is an easy way for fiddlers to collect the nutrients they need.
WHAT ABOUT BABY CRABS? When a female crab lays eggs, she holds them close to her belly until they are ready to hatch. This mass of eggs is called a sponge. When the several thousand babies hatch into the water, they are extremely tiny and look nothing like a grown-up crab. Many of the baby fiddlers are eaten by fish, but if they survive, they have plenty to eat among the smaller kinds of plankton in the water. The baby crabs molt through five different stages before becoming an adult crab after a year. They usually live 1 to 1 1/2 years total.RESOURCES:
Grimes, B.G., M.T. Huish, J.H. Kerby, and D. Morgan. 1989 Species Profile: Life Histories and Environmental Requirements of Coastal Fishes and Invertebrates (Mid-Atlantic) -- Atlantic Marsh Fiddler. US Fish & Wildlife Service Biol. Rep 82 (11.114). US Army Corps of Eng., TR EL-82-4.
Warner, G. F..The Biology of Crabs. New York: Van Nostgrand Reinhold Company, 1977.
Provided by the Pelotes Island Nature Preserve
To Invertebrates Coloring Page
To Invertebrates Fact Page