Fiddler Crabs – Photograph by Judy Drew Fairchild
Fiddler crabs are most often seen on the mud flats of outgoing tides in Lowcountry salt marshes. There are three different species of fiddlers: sand fiddlers, mud fiddlers and red-jointed fiddlers, depending on whether they are on sheltered beaches, mud flats or low-salinity brackish marshes, respectively.
They live and forage in large groups, digging burrows into the sediment. Burrows can be as deep as 2 feet, and the crabs will retreat into the burrows for resting or shelter, plugging the entrance at high tide to keep the water out.
Females have two small claws used for feeding, while males have one large claw and one small feeding claw. On warm days in the spring, you can see lots of males lined up near burrows, waving their large claws. This is a form of communication to attract females or engage in ritual combat with other males. The waving action looks as if the crab is playing the fiddle, which is how they got their name.
When fiddlers dig their burrows, they leave large pellets outside on the ground, which you are likely to see if you stop to examine one. Along with the larger pellets from excavation, you may also see smaller pellets or balls. Fiddlers feed primarily on detritus (microscopic particles of decaying organic material) that they extract from mouthfuls of sand or mud. Once they have gotten their meal, they very neatly ball up the remaining sand or mud and throw it away!
Like fiddler crabs, hermit crabs have one claw larger than the other, although the difference is not as pronounced. They also eat detritus and carrion. What makes these crabs unique is the way they occupy empty sea snail shells as a portable home. The hermit crab abdomen extends into a tapered spiral that provides a hooked appendage capable of holding the crab in place in the shell. Like other crabs, hermits molt and increase in size as they grow, but as they do that, they seek larger and larger shells to provide their homes.
Finding and keeping the right “house” is very important to a hermit crab! If a crab is too big for its shell and can’t retract into it enough to be safe from predators, it might quickly become another animal’s meal. And those in shells that are too small can’t grow as fast. As soon as a larger hermit crab leaves its shell for another one, there is often a smaller crab is waiting to move in. Two pairs of walking feet enable hermit crabs to carry a shell up to five times their body size!
There are several types of hermit crabs in Lowcountry waters. Flat-clawed hermits use their asymmetrical claws to completely close off the opening to their shell, just like the original snail would have used their operculum to close off the opening. They also play host to a variety of other organisms – slipper snails will attach to the outside of the shell, and flat slipper snails attach to the inside. Some sea anemones have also been known to hitch a ride. All of these animals take advantage of the extra particles the hermit crab doesn’t eat and use the crab as a means of locomotion through the water.
The other two kinds of Lowcountry hermit crabs are the long wristed, which can gather sea foam to feed on the fats and protein it contains, and the thin striped, which have more symmetrical front claws and is more common on muddy beaches and mud flats.
The primary crab for human consumption, the blue crab is the largest crab found in the Lowcountry. Each year, millions of pounds are caught by commercial and recreational fishermen. The Latin name is Callinectes sapidus, or beautiful swimmer. Their flat back legs serve as paddles or flippers to move them smoothly through the water, and strong front claws can catch a crabber unawares if he’s not careful!
They are beautiful: males have bright blue claws, while mature females have red-tipped claws. And like most crabs, they are opportunistic eaters that will feed on vegetation, clams, worms, fish, snails, carrion and even other crabs. Blue crabs often dig into the mud with just their eyes peeking out, waiting to ambush their next meal.
Mating usually occurs from March to July and October to November. Females carry the eggs under their abdomen, which starts out as a bright orange spot and turns darker red as the embryos develop. Females with eggs are called sponge crabs, which are protected in South Carolina (if you happen to catch one of these, be sure to put it back in the water). In about two weeks, sponge crabs make their way to water with higher salinity where eggs hatch into tiny zooplankton.
Male blue crabs are larger than females and usually reach about 7 or 8 inches. The best way to differentiate male from female, however, is to look at the abdomen. Males have a sharply pointed appendage (Washington Monument), while females have a more rounded appendage (Capitol Building). If caught, all female crabs should be thrown back in order to allow them to grow to maturity. It is illegal to keep any crab that does not measure 5 inches from point to point.
The next time you see one of these fascinating crabs on the beach or in the marsh, take a moment to stop, watch and appreciate the role they play in the Lowcountry’s complex ecosystem.
Judy Drew Fairchild is a South Carolina master naturalist and photographer who lives on Dewees Island and spends entirely too much time lying on the dock watching fiddler crabs battle each other.