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Horseshoe crabs are among the world's oldest and most fascinating creatures.

They are estimated to be at least 300 million years old. The earliest horseshoe crab species were crawling around the Earth's shallow coastal seas for at least 100 million years before the dinosaurs even arrived.

Since that time thousands of other species have come and gone, but horseshoe crabs have survived and today remain much as they were those millions of years ago, hence the nickname “living fossils.”

The spring migration of many species of shorebirds coincides with the arrival of the horseshoe crabs in the Delaware Bay. These ancient arthropods are vital to the migration of thousands of shorebirds on route to their breeding grounds in the Arctic. Relying on masses of tiny, green eggs spawned by breeding horseshoe crabs, shorebirds like the red knot descend on the Delaware Bayshores famished and at half their departure weight.  Before continuing on their epic 10,000 mile journey, these amazing birds must gorge themselves on horseshoe crab eggs sloshing against the shores of the Delaware Bay.

An Alarming Trend
Recent bird counts of migratory shorebirds have shown startling decreases in numbers. Like the link between shorebird migration and horseshoe crab spawning times, many think there is a corresponding link between shorebird population declines and horseshoe crab over-harvesting.

The loss of sandy beaches needed to lay eggs, overharvesting, particularly of females, and use of the horseshoe crabs as eel and conch bait has led to the horseshoe crabs sharp decline in population.

To help track their numbers, the University of Delaware Sea Grant Marine Advisory Service organized the first census of breeding horseshoe crabs in the Delaware Bay in 1990. For several years, The Nature Conservancy’s Delaware Bayshores program has assisted with the tracking, conducting surveys each May and June on approximately 12 peak spawning days.

Help us — volunteer for the horseshoe crab census!
The Nature Conservancy needs volunteers to assist staff with the horseshoe crab census. Surveys are conducted throughout May and June on peak spawning days at the Nature Conservancy's Sunray Beach Preserve. A census starts with an educational session that includes the biology of the horseshoe crab and step-by-step instructions on how to conduct the survey. Volunteers, armed with headlamps or flashlights, count the numbers of male and female horseshoe crabs using 1 meter square quadrants. A typical survey usually lasts two hours from start to finish.

Register to volunteer for a census by contacting Adrianna Zito-Livingston at  azito-livingston@tnc.org.

Did you know?
The horseshoe crab also has benefits to human health. Its blood, which is removed with no apparent harm to the crab, contains a clotting agent called Limulus amoebocyte lysate (LAL), which is used to test intravenous drugs, heart valves, and other prosthetics for the presence of bacterial contamination.