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 there’s 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.
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
http://pelotes.jea.com