Have you ever walked down the edge of the intertidal zone and seen small crabs scurrying busily around? These crabs are most likely fiddler crabs. There are three types of fiddler crabs common to Florida: the sand fiddler (Uca pugilator), the mud fiddler (Uca pugnax) and the red-jointed or brackish water fiddler (Uca minax). Fiddler crabs are among the most common of Tampa Bay's shoreline inhabitants. In fact, many mud flats are so packed with fiddlers the crabs make an audible sound as they scramble along the shore, like a gust of wind blowing through the reeds.
Reaching a diameter of 1-2 inches, fiddler crabs may be tan, blue-green, turquoise, black, yellow, or orange in color. They are actually darker in color during the day than during the night. Fiddler crabs live rather brief lives of no more than two years and are an important source of food for shore birds, fish, raccoons and other animals inhabiting salt marshes.
It is easy to distinguish the male fiddler crab from the female because of his one large "fiddler" claw, which he brandishes like a musician playing a fiddle to attract females and to defend his territory. During courtship, the males wave their oversized claws high in the air and tap them on the ground in an effort to attract females. Fights between males also occur, which are presumably meant to impress the females. If a male loses his larger claw, the smaller one will begin to grow larger and the lost claw will usually regenerate into a new, smaller claw.
The female fiddler carries her eggs in a mass on the underside of her body. She remains in her burrow during a two-week gestation period, after which she ventures out of the burrow to release her sponge (fertilized eggs) into the retreating tide.
As you walk along the intertidal zone you may see mounds of sand next to small holes. This is sand that the crabs sift in search of food, primarily algae or decaying plant matter. This sifting process actually helps to aerate the sediment around marsh grasses, thus helping them grow. It is actually easier for female fiddlers to gather food than for males, since the females have two small, nimble claws while the males are hampered by their large fiddler claw. Fiddlers also play an important role in the marine food web, since they serve as dinner for a variety of fish, wading birds and even raccoons.
Fiddler crabs live on sandy or muddy shores that are exposed during the low tide, and each crab lives in a hole it digs for itself. During high tide, fiddler crabs plug the entrance to their burrows with mud and wait until the tides goes down again in a cozy den from 1 to 3 feet beneath the surface. They must leave an air pocket in their burrows, since they obtain oxygen from the atmosphere.
At low tide, the crab abandons its home in search of food, but never strays far, unless it is courting a female or scaring away a nosy neighbor.
Fiddler crabs are a popular bait for anglers in Tampa Bay, who use them to catch sheepshead, pompano and black drum, among other species.