The ancient migration of horseshoe crabs (Limulus polyphemus) has commenced along the shores of Maryland. This annual event, dating back approximately 350 million years, is considered the oldest and largest wildlife migration globally. It typically occurs from May through July, with peak activity during high tides around the full and new moons in May and June.
Each spawning season, a single female horseshoe crab can lay around 20,000 eggs in the sand. These eggs play a crucial role in the ecosystem, serving as a primary food source for migratory shorebirds preparing for their journey to summer nesting grounds in northern Canada. Additionally, the larvae are vital for juvenile Atlantic loggerhead turtles and various fish species, including striped bass, American eel, and flounder.
Horseshoe crabs are also invaluable to humans due to their copper-based blood, which is essential for biomedical research. The crabs are collected by permitted fishing operations, bled at biomedical facilities, and then released back into the water. This process helps ensure the safety and efficacy of medical products.
Despite their intimidating appearance, horseshoe crabs are harmless creatures. Their tails, often mistaken for weapons, are used for navigation and self-righting when flipped over. Humans can assist horseshoe crabs by gently flipping them back onto their feet if found trapped or overturned. It is important to handle these animals carefully, using both hands and never lifting them by the tail.
The Maryland Department of Natural Resources (DNR) and the Maryland Coastal Bays Program monitor the horseshoe crab population for ecological and scientific research. The DNR encourages the public to report any sightings and spawning activities via the Horseshoe Crab Volunteer Angler Survey.
The best time to observe this migration is during the evenings around the new and full moons in June. Prime viewing spots include Sunset Park near the Ocean City Inlet and various spawning sites around the Chesapeake Bay listed on the Horseshoe Crab Volunteer Angler Survey webpage.
