Horseshoe crabs: Strange 10-eyed sea creatures that chew with their legs facing extinction

Nature’s consummate survivors may now be in peril

Sarah Kaplan

All along the shoreline, for as far as you can see, slick shells of horseshoe crabs glisten in the fading daylight. Listen closely, and you can hear their subtle clacking and the whisper of water over their carapaces.

It's horseshoe crab spawning season in Delaware Bay. Every May and June, on nights when the moon is new and the tide is high, they crawl onto the beach to mate and bury their eggs.

The ritual goes back 445 million years. Horseshoe crabs are living fossils that have survived four mass extinctions. They are bizarre creatures with 10 eyes that offer insights into how vision evolved. And their blood has saved countless human lives - including yours.

But these creatures, nature's consummate survivors, are in peril. And to protect them, it's urgent that biologists understand their life cycles and learn how many there are. That's why researchers are out in force this night, working quickly to take a census of the crabs before they disappear beneath the waves.

Elle Gilchrist reaches into a pile of crabs. Each is glossy green-brown and shaped like a shallow combat helmet with a six-inch spine sticking out the back. Gilchrist, a 20-year-old intern with the Delaware National Estuarine Research Reserve, who sports a long blond ponytail, galoshes and silver horseshoe-crab-shaped earrings, expertly flips a crab over to reveal 10 segmented legs and a sheaf of sturdy gills. The males' limbs end in pincers, which they use to grab onto prospective mates. The insides of the females' carapaces are lined with thousands of tiny pale green eggs - the reason for tonight's festivities.

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