On warm summer nights along the Ocean City shoreline, thousands of armored creatures emerge from the surf under the glow of the boardwalk’s Ferris wheel, their domed shells gleaming as they scurry across the sand in search of mates. These are Atlantic horseshoe crabs, often described as living fossils, undertaking one of nature’s most enduring rituals—a migration that has persisted for roughly 450 million years.
Biologists with the Maryland Department of Natural Resources have been documenting this spectacle each season as part of long-term monitoring. Steve Doctor, who has overseen the state’s horseshoe crab program since 2003, leads teams that head to key spawning beaches on eight nights during the peak period. The timing aligns with the highest tides around the full and new moons from May through July, when conditions are ideal for the crabs to come ashore.
Horseshoe crabs are not true crabs but belong to an ancient group of arthropods known as Xiphosura, more closely related to spiders and scorpions than to crustaceans. Their distinctive appearance—a hard, horseshoe-shaped carapace and a long, pointed tail called a telson—has remained remarkably consistent through deep time. Fossils dating back to the Jurassic period, around 148 million years ago, look nearly identical to the animals seen today on the Atlantic coast. Scientists refer to them as stabilomorphs because they have changed so little, a testament to how perfectly adapted they are to their ecological role.
Four species of horseshoe crabs exist worldwide, with the Atlantic variety ranging from Nova Scotia down to the Yucatán Peninsula. In Maryland, the annual spawning draws large numbers to beaches around the Ocean City inlet, Assateague Island, and other coastal spots. Females, which are larger, crawl onto the sand, dig shallow nests, and deposit thousands of tiny green eggs. Males cluster around them, releasing sperm to fertilize the eggs before the tides cover them again. The entire process is a frenzy of activity that can transform quiet stretches of beach into bustling scenes reminiscent of prehistoric times.
The ecological importance of these eggs extends far beyond the crabs themselves. During spring and early summer, millions of migratory shorebirds, including red knots, rely on the nutrient-rich eggs as a critical refueling stop along the Atlantic flyway. The Delaware Bay region, which includes Maryland’s coastal waters, hosts one of the largest concentrations of spawning horseshoe crabs on the planet, making it a vital link in the chain for bird populations traveling between South America and the Arctic.
For decades, that link was under strain. In the 1990s, horseshoe crab populations in the Delaware Bay area dropped sharply. Overharvesting for use as bait in eel and whelk fisheries drove much of the decline, with coastwide landings surging nearly 600 percent between 1990 and 1997. At the same time, biomedical companies began collecting large numbers of crabs to produce Limulus Amebocyte Lysate, or LAL, a substance derived from their blue blood that detects bacterial contamination in vaccines, injectable drugs, and medical devices. While many crabs are released after bleeding, mortality rates from the process have been estimated around 15 percent in official figures, with some studies suggesting higher impacts, particularly for females, along with temporary effects on spawning behavior.
The drop in horseshoe crab numbers had ripple effects. Red knot populations, which depend heavily on the eggs during their northward migration, fell from roughly 50,000 birds in the late 1990s to about half that number within a decade. Scientists and managers recognized the connection and took action. In 1998, the Atlantic States Marine Fisheries Commission adopted a coastwide management plan for horseshoe crabs. New Jersey imposed a full moratorium on commercial harvest, while Maryland, Delaware, and Virginia implemented male-only quotas and banned the taking of females. An innovative Adaptive Resource Management framework was later developed to tie harvest limits directly to the needs of dependent shorebirds like red knots.
The results have been encouraging. A detailed analysis published in 2025 in the journal Marine and Coastal Fisheries examined multiple trawl survey datasets from New Jersey, Delaware, Maryland, and Virginia. It showed the regional population declined from the early 1990s through about 2005, stayed relatively low and stable until around 2010, then began a steady climb. By 2023, overall abundance had returned to levels comparable to—or in some analyses slightly above—those recorded in 1990, before the period of heavy exploitation. Recent Atlantic States Marine Fisheries Commission assessments describe the Delaware Bay stock as “good,” with similar positive status in the Southeast region. The Northeast is considered stable, while the New York area remains in poorer condition.
Maryland’s contribution to this recovery includes rigorous local monitoring. In addition to the spawning beach surveys in the Ocean City area, state biologists conduct seine and trawl surveys that have been running continuously since 1972. These efforts help track abundance, size distribution, and recruitment of young crabs. During peak spawning nights in June, teams set up transects on beaches such as Skimmer Island and sections of Assateague, methodically counting crabs within defined areas to estimate total numbers on the spawning grounds.
Despite the clear rebound in horseshoe crab numbers, red knot populations have not shown a corresponding strong increase and remain relatively stable at lower levels than historical peaks. Researchers are exploring possible explanations, including conditions on Arctic breeding grounds, habitat changes elsewhere along the migration route, or a lag in the birds’ response to improved food availability. The situation illustrates that ecosystem recovery can be complex and that protecting one species does not automatically restore all dependent species.
Public engagement plays an important role in ongoing conservation. Residents and visitors can report spawning activity or help with simple rescues of overturned crabs through volunteer programs coordinated by the Department of Natural Resources and partners like the Maryland Coastal Bays Program. Best practices include gently flipping crabs without lifting them by the tail, which can cause injury. Prime viewing locations in Maryland include areas near the Ocean City Inlet and Assateague Island beaches during the highest tides of the new and full moons.
The biomedical industry continues to rely on horseshoe crab blood for LAL testing, though synthetic alternatives known as recombinant Factor C are gaining traction and could eventually reduce pressure on wild populations. In the meantime, strict handling protocols and limits on collection help minimize impacts. Bait harvest remains regulated through quotas that prioritize sustainability.
For Marylanders, the annual return of horseshoe crabs to coastal beaches represents both a natural wonder and a symbol of successful resource management. The species’ long evolutionary history—surviving multiple mass extinctions—offers perspective on resilience, while modern efforts show that targeted conservation can reverse declines even for species facing intense human pressures.
As the 2026 spawning season progresses, biologists will continue gathering data that informs future decisions. The combination of scientific monitoring, regulated harvest, and public awareness has helped bring the Delaware Bay horseshoe crab population back to healthier levels. These ancient creatures, with their distinctive shells and purposeful march onto the sand, continue to connect Maryland’s present-day coastal communities with a deep natural heritage that spans hundreds of millions of years.
