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Blue Bloods

Blue bloods have been swarming the beaches of Hilton Head and its neighboring sea islands for pretty much forever. But they're not who you think they are. They're actually a bit crabby.

The First Tourists

If you're lucky enough to have strolled the Lowcountry's beaches, you've likely encountered a few strange-looking helmet-shaped, long-tailed creatures lying on the shore. More likely, you've found their empty shells. These are American horseshoe crabs, and they've existed on our planet for more than 450 million years, long before dinosaurs roamed the earth or the American continents came to be. These "living fossils" watched the rise and fall of millions of other species, surviving ice ages and meteor strikes to enter our own era virtually unchanged. Actual fossils of prehistoric horseshoe crabs (see photo above) have been found throughout the planet, and today these amazing animals call the Carolina Sea Islands home.

"Big Brown"

Horseshoe crabs get their name from their hinged, u-shaped hard outer shell, although some islanders refer to them as "Big Brown" in reference to their usual color. The underside of the animal resembles a scorpion, with a pair of tiny foreclaws for eating and ten walking legs (see photo, left). Its sharp tail is not a weapon, but rather a rudder to help it steer while swimming, or a cane to aid in flipping itself over if upended by a wave. Don't be alarmed if you see an empty horseshoe shell lying on the Sea Island sand. This is completely normal and does not indicate that the crab has died. Ranging in size from 2 inches to 2 feet from head to tip of tail, Big Browns shed their shells periodically as their soft bodies grow, then develop a new,

larger shell. When these crabs come ashore, it is often to find a mate. You'll know they've been there by their tracks--small claw marks surrounded by straight lines where their shell and tail have dragged across the sand (see photo, right). But what do horseshoe crabs have to do with blue bloods?


Given the longevity of their species, these incredible animals are clearly resilient--a fact that modern scientists have utilized to help keep the human species alive. Bright blue in color, copper-rich horseshoe crab blood (see photo, top) contains important immune cells that are exceptionally sensitive to toxic bacteria. When those cells meet invading bacteria, they clot around it and protect the rest of the horseshoe crab's body from toxins. Since the 1970s, scientists world-wide have used these blood cells to check new human vaccines (including those for COVID-19) for contamination. This technique has been lifesaving for humans, but

not so great for the horseshoe crabs, which are rounded up by the thousands and bled each year. Although the animals are generally returned live to the water within 36 hours, this controversial process has drawn the ire of animal welfare groups. They note high numbers of horseshoe crabs who do not survive this biomedical harvesting, as well as decreased spawning rates post-bleeding. Unfortunately, synthetic crab blood has not yet proven as successful as the real thing, so many countries--including the United States--still bleed live crabs.

While pharmaceutical developers are becoming more careful about keeping population numbers healthy, any threat to the species' numbers is not apparent on our Sea Island beaches. Horseshoe crabs are a common sight on our shores, and hopefully will remain so for the next few million years.

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1 Comment

Jeanne Mascott Befano
Jeanne Mascott Befano
Jul 18, 2023

Thank you for sharing this! I learned so much and will 'see' these amazing creatures differently now. I'm especially happy to know that their empty shells are not an indication that they've died, but rather,moved to larger quarters!

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