06/20/2025
International Horseshoe Crab Day is celebrated every year on June 20th to raise awareness about one of Earth’s most ancient and fascinating creatures—horseshoe crabs. These marine arthropods have been around for over 400 million years, earning them the nickname “living fossils”.
But this day isn’t just about marveling at their longevity. It’s a call to action. Horseshoe crabs are vital to both ecosystems and human health. Their eggs are a crucial food source for migratory birds, and their unique blue blood contains a compound called limulus amoebocyte lysate (LAL), which is used to test vaccines and medical equipment for bacterial contamination. In other words, if you've ever had a safe injection or surgery, you might have a horseshoe crab to thank.
The Monomoy National Wildlife Refuge and horseshoe crabs have a very special relationship. The Refuge is one of the few places in New England where large numbers of horseshoe crabs still spawn in significant numbers each spring.
This spawning event is critical not just for the crabs, but for migratory shorebirds—especially the Red Knot, a federally threatened species. These birds travel thousands of miles from South America to the Arctic, and they rely on the protein-rich eggs of horseshoe crabs to refuel during their journey. Monomoy serves as a vital stopover where Red Knots and other shorebirds like Ruddy Turnstones and Sanderlings feast on the eggs laid in the sand.
Without healthy horseshoe crab populations at Monomoy, these birds might not survive the rest of their migration. So, protecting the crabs here means protecting an entire migratory network that spans continents. It’s a quiet but powerful drama that plays out each spring on the refuge’s tidal flats and sandbars.
Unfortunately, these creatures face serious threats from overharvesting, habitat loss, and climate change. That’s why International Horseshoe Crab Day was established in 2020 by the IUCN’s Horseshoe Crab Specialist Group—to spotlight conservation efforts and encourage global cooperation to protect all four species of horseshoe crabs.
It’s a day to celebrate resilience, but also to reflect on how we can coexist with a species that’s survived mass extinctions, only to be endangered by modern human activity!
You can view a short video of our Horseshoe Crab friends on the Refuge's South Monomoy Island here...https://youtu.be/S8uMo4tiLvI