Thousands of horseshoe crabs (Limulus polyphemus) are arriving on Maryland’s shores for their annual spawning, a migration believed to be the world’s oldest, dating back 350 million years. From May through July, peaking around the full and new moons in June, these ancient creatures deposit eggs vital to ecosystems and medical research. The Maryland Department of Natural Resources (DNR) encourages public reporting of sightings to aid conservation efforts.
Each spawning female horseshoe crab lays about 20,000 eggs in the sand, with a male fertilizing them as he clings to her shell. The eggs serve as a critical food source for migratory shorebirds heading to northern Canada for summer nesting. Horseshoe crab larvae also feed juvenile Atlantic loggerhead turtles, striped bass, American eel, and flounder. Beyond ecology, the crabs’ copper-based blood is harvested by specially permitted fishing operations for biomedical testing of bacterial products, with the crabs released after blood collection.
Despite their armored appearance and long tails, horseshoe crabs are harmless, neither biting nor stinging. Their tails, often mistaken for weapons, help them navigate sand, steer in water, and flip over if overturned. The DNR advises the public to assist stranded crabs by gently flipping them using both hands, avoiding the tail. Ideal viewing times are evenings around the June full and new moons, on June 11 and June 25 in 2025, at locations like Sunset Park near the Ocean City Inlet or Chesapeake Bay spawning sites listed on the DNR’s Horseshoe Crab Volunteer Angler Survey webpage.
DNR biologists, alongside the Maryland Coastal Bays Program, monitor horseshoe crab populations for ecological and scientific research. The Volunteer Angler Survey collects public reports to track spawning activity and population health. “The survey helps us understand horseshoe crab distribution and spawning trends,” a DNR spokesperson said. This data informs conservation strategies for the species, which faces threats from habitat loss and overharvesting.
Horseshoe crabs play a unique role in Maryland’s coastal ecosystems. Their eggs and larvae support a food web that sustains migratory birds and marine life, while their blood advances human health through medical testing. The spawning season draws attention to the delicate balance of preserving this ancient species while supporting biodiversity. Public participation in reporting sightings strengthens research efforts, ensuring the crabs’ survival for future generations.
The crabs’ migration, unchanged for millions of years, offers a glimpse into prehistoric life. Their resilience has outlasted countless species, yet modern challenges like coastal development and climate change pose risks. The DNR’s monitoring programs aim to mitigate these threats by studying population trends and habitat needs. Volunteers play a key role by reporting sightings, particularly during peak spawning in June, when high tides bring crabs to shore in large numbers.
Viewing horseshoe crabs is a family-friendly activity, with Sunset Park and other coastal sites providing accessible observation points. The DNR emphasizes respectful interaction, urging the public to avoid disturbing spawning crabs or damaging their eggs. By following guidelines, such as not lifting crabs by their tails, visitors can help protect this ancient species while enjoying a natural spectacle.
Maryland’s efforts to monitor and conserve horseshoe crabs reflect a broader commitment to coastal ecosystems. The data collected through public reports and scientific research will guide future policies to safeguard the species and its habitat. As spawning continues through July, the DNR encourages residents and visitors to participate in the survey and witness one of nature’s oldest migrations.
