Ghost Crabs

By some accounts St. Augustine is a very haunted city, but your odds of seeing a ghost are probably greater on the area’s beaches than anywhere else, at least if the apparition takes on the appearance of a crab! What makes this crab ghostly is its sand-colored exoskeleton (or carapace), which helps it disappear into its surroundings. Possibly also the fact that it is most commonly seen from dusk through dawn when it roams the beach looking for food. Or maybe that it scuttles about (forward, sideways, and in reverse) on six hairy legs at up to ten mph (faster than any other land crustacean!). Or could it be those two stalked eyes that allow it to see acutely in 360 degrees, at least when they aren’t pulled into grooves on the front of its shell for protection? But if the beaches and dunes are going to be haunted by anything, the ghost crab is a friendly ghost indeed, for its presence is indicative of a healthy environment.

The reason ghost crabs are associated with healthy Florida beaches stems from their eating habits. They eat a lot of different things, and if a beach can’t support a rich and diverse food supply, the crabs can’t survive either. Some of their common prey include coquina clams, mole crabs, beach fleas, lizards, and even flying insects that venture too close. This crab comes equipped with two strong claws of unequal size, each tipped with sharp pincers. They use these appendages to crush their prey before eating it. This also allows them to go after larger food items such as shorebird eggs and chicks and sea turtle eggs and hatchlings. (More sea turtle eggs are eaten by ghost crabs on a seasonal basis than by any other animal except for raccoons.) But when they can’t find something fresh to eat, the ghost crab is perfectly happy to consume carrion, and a dead fish washed up on the beach is a feast indeed. However, life is a two-way street, and ghost crabs make delicious meals for raccoons, birds, and even humans on some Caribbean islands.

In addition to helping keep the beach clean of dead animals, another service ghost crabs provide is to aerate the soil by digging burrows into the sand (sometimes opportunistically right next to a dead critter!). The entrance to their burrows are about golf ball-sized on average, are made in moist sand for stability, and can run four feet deep, with a chamber at the end large enough for the crab to turn around. During cold winter months, the crabs hibernate in their burrows located higher on the beach, and breath oxygen from specialized sacs located near their gills. Normally though they must keep these gills moist as they go about their daily lives. They do this by scurrying down to the shore and letting the surf get them wet. Between dips in the surf they can store a small amount of seawater in their bronchial chambers to get them by. Another reason you may see a ghost crab enter the swash zone is if she’s a female carrying an egg mass. The eggs must be kept wet until they hatch.

But ghost crabs are called ghosts for a reason, and it’s not always easy to spot them during the heat of the day. But keen beachcombers will almost always see their tracks, especially emanating from their burrows. The tracks look like six rows of distinct comma shapes. Their presence is an indication of a busy nocturnal creature that will unearth itself again once the sun sets to haunt the beach in search of its next life-sustaining meal.