Ghost crabs are fascinating inhabitants of sandy beaches across tropical and subtropical regions worldwide. These semiterrestrial crustaceans are well-adapted to life both on land and near the water’s edge. Their presence often indicates a healthy beach ecosystem, making them a subject of interest for both casual observers and scientists. Ghost crabs are known for their elusive nature and their ability to blend seamlessly into their surroundings, leading to their common name.
Identifying Features
Ghost crabs have distinct physical characteristics. They typically have pale-colored bodies, ranging from off-white to sandy or grayish-white, which provides effective camouflage against the sand. Some species, like the painted ghost crab, can exhibit brighter coloration. Their shell, or carapace, is often squarish or box-like, measuring up to 3 inches (about 5-8 cm) across in mature adults, with males generally being larger than females.
Their large, elongated, club-shaped eyestalks are a key feature. These eyestalks can extend significantly, with the cornea occupying the entire lower portion. In some species, such as the horned ghost crab, these eyestalks can even have horn-like extensions. Ghost crabs have four pairs of walking legs, which are longer than their claws, enabling swift movement across the sand. They also have a pair of claws (chelipeds), one of which is typically larger than the other in both males and females, a trait that differentiates them from fiddler crabs where this is usually only seen in males.
Life on the Beach
Ghost crabs inhabit open sandy beaches in tropical and subtropical climates globally. They prefer the supralittoral zone, the area above the high tide line, extending into the dunes. These crabs are expert burrowers, constructing deep and complex burrows that can extend up to 4 feet (1.3 meters) deep. These burrows serve multiple purposes, providing shelter from predators, protection from extreme weather conditions, and a moist environment to prevent desiccation. Younger crabs often dig burrows closer to the water, while older, larger crabs may establish their homes further inland.
Ghost crabs are primarily nocturnal, emerging from their burrows after dusk to forage and remain active until dawn. This nocturnal behavior helps them avoid visual predators like shorebirds during the day. Their diet is varied, classifying them as generalist scavengers and predators. They feed on carrion, debris, and small animals found on the beach, including sea turtle eggs and hatchlings, clams, mole crabs, and insects. They may also consume decomposing plant matter.
Survival Skills
Ghost crabs have remarkable adaptations for their challenging beach habitat. Their most notable trait is their high speed, with the scientific name Ocypode meaning “swift-footed.” They can dart across the sand at speeds up to 10 miles per hour (4.5 meters per second), making them among the fastest crustaceans. This agility allows them to escape predators quickly and effectively capture prey.
Their vision is impressive, with their large, club-shaped eyestalks providing a nearly 360-degree field of view. While they cannot see directly overhead, this wide range of vision helps them spot both predators and prey. Ghost crabs can also retract their periscope-like eyes into grooves on their shell for protection. They also have specialized gills; although semi-terrestrial, they must keep their gills moist to breathe oxygen from the air. They achieve this by periodically returning to the water’s edge or by wicking up water from damp sand using fine hairs at the base of their legs.
Ghost crabs exhibit effective camouflage. Their pale coloration blends seamlessly with the sand, making them difficult to spot. They can change their body color to match their surroundings by adjusting pigment concentration in their chromatophores. Some species, particularly juveniles, even show a circadian rhythm of color change, becoming lighter during the day and darker at night, which aids in camouflage regardless of ambient light conditions.