Uca pugilator

The fiddler Crab has about 90 species. The male has one claw which weighs about 25% to 1/3rd or more of its body weight. This claw is primarily to impress females to mate with him. Two other fiddler crabs which are very similar range up the Atlantic Coast. They are the Uca pugnax or mud fiddler and the Uca minax or red-jointed fiddler.

So why are they called fiddler crabs. A fiddler eats with its small claw grasping food and placing it into its mouth. With the large claw on one side, as the small claw goes back and forth to the mouth, it looks somewhat like a violinist playing a violin.

Here is a little on the taxonomy of the sand fiddler crab (Uca pugilator) and other fiddlers:

This is a sand fiddler Crab from McFadden Beach, Jefferson County, Texas

Male fiddler crabs can be recognized easily by the vast difference in the size difference between their right and left claws. Females have essentially the same size claw on right and left. The body of both sexes are somewhat rectangular with the front of the crab being wider than the back, but somewhat box like. Crabs have ten appendages, with eight legs and two pincher claws.

As the male fiddler crab grows to maturity, the relative weight of its large claw, or cheliped, changes from 2% to 65% of its total body weight. 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 claw is needed for gathering food. Some species of fiddlers live in large groups, which helps them to spot predators more easily. This can be birds animals and other marine life.

There are several types of fiddler crabs including, but not limited to, sand fiddlers, mud fiddlers and marsh fiddlers. Fiddlers live in salty or brackish water. They need both high spots of land and this type of water to live successfully. They like to live near water on the mud or sand.

Male fiddler crabs use the oversized claw by waving it up and down. This is to attract females for mating and also to intimidate rival male suitors. Fiddlers stomp their eight walking legs and make noises with these legs as part of their effort to attract females. These displays build up to a peak during spring tides. Female crabs enter the male's burrows, where the mating takes place. A female fiddler then remains inside the male's burrow during the 2-week incubation period. After that she comes out to release her eggs into the water, where they are swept out to sea by outgoing tide. After fiddler eggs hatch, fiddler larvae go through several developmental stages. There are six stages, five of which are called zoeae and the sixth a megalopal. This takes about two-weeks as they are adrift in the ocean.

The fiddlers are then transported back inside estuaries on the following spring tide. The fiddler larvae are predatory. They eat zooplankton in the water column. Fiddlers remain pelagic for some time after reaching the sixth or megalopal stage. Then fiddlers gradually adopt a benthic (land) existence. Adult mud fiddlers feed on organic material extracted from mud. The mud fiddler rolls the mud into small balls after the food is removed and deposits the ball back onto the substrate. Pellets formed during burrow excavation are much larger than feeding pellets. Mud fiddlers are adept at regulating their metabolism over a wide range of temperatures, which may explain their widespread abundance.

Male sand fiddlers find their food on the beach, which is often sewn with dead fish and other marine life.

Fiddlers dig burrows which are about 1/2" wide and go as much as a foot, almost straight down into the mud or sand. Fiddler crabs tunnels may connect with other tunnels and have more than one entrance. These burrows provide a quick escape from predators like water birds, raccoons and even predatory fish. Fiddler's burrows offer a cool shady place to escape the sun also. During high tide, burrows are a place for the crabs to stay until the tide goes back out. During low tide fiddlers look for food but stay near their burrows. If danger comes and a fiddler is too far from his own burrow, it will pop into any convenient burrow to escape.

During high tide, fiddlers often roll up a ball of mud or wet debris, to plug the hole of their burrow. This traps a small pocket of air in the burrow for the fiddler to breath, until the tie goes back out. All crabs have gills, but crabs that live on land, like the fiddlers, breathe air instead of water. However, fiddlers must stay near water at all times, as their gills must stay wet to work.

The mud fiddler, Uca pugnax, has an H-shaped depression in the middle of the carapace and its' eyestalks are long and thin. It is brown in color, with the front of the shell and eyestalks ranging from blue to turquoise. The large claw of the male is usually yellowish orange to yellowish white, and its walking legs are dark and banded. The size of the claw varies from species to species, but it is always very large.

The sand fiddler, mud fiddler and red-jointed fiddler are easily differentiated on the basis of anatomical features and preferred habitat: sand fiddlers inhabit sandy habitats, they are typically a pinkish-purple color, and the inside of the male’s large claw lacks a row of small bumps; mud fiddlers are a brownish-yellowish color, they prefer muddy areas, and the inside of the male’s large claw has a row of small granules; red-jointed fiddlers are larger than the other two species, and the joints of the male's large claw are red.

Fiddler crabs are one of the most conspicuous inhabitants of the intertidal zone, and they often can be seen foraging in large groups along creek banks when the tide is out. They thrive in marsh habitats where the substrate is stable enough to allow for the construction of burrows, which can be up to 60 cm (23 in) deep. Sand fiddlers range throughout the Gulf Coast area. Mud fiddlers range from Massachusetts to Florida and are common along the South Carolina coast.

Fiddlers have no apparent commercial value, however they constitutes an important food source for other estuarine animals. This includes birds, blue crabs, fish and other animals. As are other estuarine-dependent animals, fiddler crabs are under continuously increasing threat of habitat loss due to land use practices that alter or destroy suitable habitat.