Credit: Willy Conley / Maryland Department of Natural Resources
Thousands of horseshoe crabs have begun their annual spawning migration along Maryland’s shores, one of the oldest wildlife events on Earth. The prehistoric creatures, which have existed for an estimated 350 million years, are returning to Chesapeake Bay beaches and coastal areas from May through July, with peak activity expected around high tides on or near the full and new moons in June.
In 2026, those peak dates fall on June 15 and June 29. Biologists say one spawning female can lay an average of 20,000 eggs in the sand, with a male often attached to her shell to fertilize them as they are deposited. The eggs provide a vital seasonal food source for migratory shorebirds, including red knots, that stop along the Atlantic Flyway before continuing north to nesting grounds in Canada. Horseshoe crab larvae also serve as an important food source for juvenile Atlantic loggerhead turtles, striped bass, American eel and flounder.
The Maryland Department of Natural Resources and the Maryland Coastal Bays Program monitor the returning population each spring for ecological and scientific research. The department is encouraging the public to report spawning activity and sightings through the Horseshoe Crab Volunteer Angler Survey. Reports help biologists better understand spawning habitat and population trends across the state.
Horseshoe crabs are not true crabs. They are more closely related to spiders and scorpions. Despite their hard shells and long tails, they are gentle creatures that do not bite or sting. The tail is used as a rudder in water, to plow through sand and mud, and to right themselves when flipped over. If a horseshoe crab is found upside down in a rocky area, people are encouraged to gently flip it over using both hands — never by the tail, which can be damaged.
The animals also play a critical role in human medicine. Their copper-based blood is used to produce Limulus amebocyte lysate, a reagent that tests for bacterial endotoxins in medical products and vaccines. Specially permitted operations collect horseshoe crabs, draw a small amount of blood in a controlled facility, and release the animals back into the water.
For Southern Maryland residents, the migration is a visible sign of the Chesapeake Bay’s living history. Spawning can often be observed along the Bay’s western shore in Calvert, St. Mary’s, and Charles counties during evening high tides in late May and June. Popular viewing spots include protected beaches and shoreline areas listed on the DNR’s volunteer survey map.
The best opportunities to see large numbers of horseshoe crabs are in the evenings around the full and new moons in June. In addition to Chesapeake Bay sites, spawning activity is commonly observed near Sunset Park by the Ocean City Inlet on the state’s coastal bays.
DNR biologists note that while the migration is a natural and impressive event, horseshoe crab populations face ongoing pressures from habitat loss, climate change and historical overharvesting. The annual volunteer survey helps track trends and supports long-term conservation efforts.
