Horseshoe Crab Spawning Migration Arriving in Maryland
These horseshoe crabs landed at Chesapeake Beach on the western shore of the Chesapeake Bay in 2024. Photo by Elizabeth Klein, Maryland Department of Natural Resources.
Thousands of horseshoe crabs (Limulus polyphemus) have begun landing on Maryland’s shores for what is believed to be the world’s oldest wildlife migration. Dating back an estimated 350 million years, the annual spawning occurs from May through July, peaking with high tides on or around the full and new moons in June.
One spawning female horseshoe crab will deposit an average of 20,000 eggs into the sand, with a mate grasping onto her shell, fertilizing the eggs as they move. In addition to perpetuating the ancient species, the eggs are a seasonal buffet for migratory shorebirds preparing to return to their summer nesting grounds in northern Canada. Horseshoe crab larvae are also an important food source for juvenile Atlantic loggerhead turtles, striped bass, American eel, and flounder. For human health, the horseshoe crab’s copper-based blood is also used for testing for bacterial products used in medicine. Specially permitted fishing operations collect the animals, draw their blood in a biomedical facility, and release them back into the water.
Despite their armor and tail, horseshoe crabs are gentle creatures that do not bite or sting. The tail is not a weapon; it is used to plow the crab through the sand and muck, act as a rudder in the water, and to right the crab when it accidentally tips over. Humans can help horseshoe crabs stuck upside down in rock jetties by gently flipping or moving the animal, using both hands, but never picking it up by its tail.
Maryland Department of Natural Resources biologists and the Maryland Coastal Bays Program monitor the returning horseshoe crab population for ecological and scientific research purposes. The department encourages the public to report any spawning activity and sightings of horseshoe crabs to DNR’s Horseshoe Crab Volunteer Angler Survey.
The best opportunities to view horseshoe crabs are evenings around the full and new moons in June (June 11 and June 25 in 2025). Ideal locations for observation include Sunset Park near the Ocean City Inlet, and they can also be seen around the Chesapeake Bay at spawning sites listed on the Horseshoe Crab Volunteer Angler Survey webpage.
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