Horseshoe Crabs: Merostomata

Physical characteristics: The horseshoe crab, also known as American horseshoe crab, is greenish brown to blackish brown. Males are smaller than females. The average body length of males is 14 inches (356 millimeters) and of females is 17 inches (431 millimeters).

Geographic range: The horseshoe crab inhabits the Atlantic and Gulf coasts of North America, from Long Island to the Yucatán peninsula.

Habitat: These crabs live off the coast to depths of more than 200 feet (61 meters).

Horseshoe crabs inhabit coastal regions of eastern North America and the Indo-Pacific. (© John M. Burnley/The National Audubon Society Collection/Photo Researchers, Inc. Reproduced by permission.)

Diet: The horseshoe crab eats clams and marine worms.

Behavior and reproduction: Adults live in deeper, offshore waters during the winter, ranging as far out as 25 miles (40 kilometers). In spring they migrate into shallow waters and then onto sandy beaches to spawn. Males approach the beach as the tide rises, followed by the females. Spawning occurs mostly at night near the high-tide line. Females bury as many as twenty thousand eggs in several clutches, or groups, which are fertilized by males. Eggs hatch after thirteen to fifteen days.

Horseshoe crabs and people: In the United States the horseshoe crab is harvested as bait for the conch and eel fisheries. From 1850 until the 1970s the horseshoe crab was processed for fertilizer. Components of its blood and exoskeleton are used for a wide variety of medical purposes.

Conservation status: This species is listed by the World Conservation Union (IUCN) as Near Threatened. It is threatened by too much harvesting and habitat destruction. ∎