Horseshoe Crab
Limulus polyphemus · Arthropod, Invertebrate, Cold-blooded, Wild
Animal Family
Family Limulidae, Order Xiphosura, Class Merostomata
Animal Category
Marine Animal
Breed / Variety
Atlantic Horseshoe Crab
Conservation Status
IUCN Red List status is Vulnerable. Population trend is decreasing due to overharvesting for use as bait in the conch and eel fisheries, biomedical harvesting of their blue blood for endotoxin testing, and coastal habitat loss from shoreline development.
About This Creature
The horseshoe crab has a hard, dome-shaped exoskeleton resembling a horseshoe, divided into a prosoma (head region), opisthosoma (abdomen), and a long, spiked telson (tail). Adults range in size from 12 to 19 inches long including the tail. Their coloration ranges from dark brown to olive-green. They have multiple eyes, including compound eyes and simple ocelli, and book gills underneath for respiration.
Physical Characteristics
Hard chitinous carapace, five pairs of walking legs with the first pair modified in males for grasping during mating, book gills situated on the abdomen, a rigid spine-like telson used for righting itself when flipped over, and blue, copper-based blood containing amoebocytes.
Behavior & Temperament
Solitary creatures for most of the year, becoming social only during the spring and summer breeding seasons when they migrate in large numbers to intertidal beaches. They are slow-moving, primarily nocturnal, and bury themselves in sand or mud. They use their telson to flip over if stranded upside down and communicate primarily through chemical cues during mating.
Habitat & Diet
Origin Region
Coastal waters of Eastern North America and the Gulf of Mexico, extending along the Atlantic coast from Maine to the Yucatan Peninsula
Habitat
Shallow coastal marine waters and intertidal zones, benthic and aquatic
Diet & Nutrition
Carnivorous scavenger and benthic feeder. Diet consists primarily of marine worms, clams, small mollusks, crustaceans, and organic detritus. They use their bristled legs to crush food and push it into their central mouth located between their legs.
Lifespan & Health
Lifespan in the wild is typically 20 years or more. Predators include sea turtles, sharks, rays, and migratory shorebirds that feed on their eggs. Females lay clusters of eggs in nests on sandy beaches, going through multiple molting stages over nearly a decade to reach sexual maturity.
Special Characteristics
Known as living fossils because they have remained virtually unchanged for over 450 million years. Their unique blue blood contains Limulus Amebocyte Lysate (LAL), which is critically important for detecting bacterial endotoxins in pharmaceutical products and medical devices. Despite their menacing appearance and tail, they are harmless to humans and do not possess stingers.
Ecological Information
Serves a vital ecological role as a key food source for migrating shorebirds, such as the red knot, which time their migrations to feed heavily on horseshoe crab eggs. They also contribute to nutrient cycling in benthic marine environments and support numerous commensal organisms that live on their shells.