horseshoe crab
PHOTOGRAPH BY TIMOTHY FADEK/CORBIS

The Surprising Creatures Vaccines Are Tested On

There’s a lot to be gotten from a connection to a crab that’s been lurking in the oceans for half a billion years.

September 8, 2015

A scruffy arc of sand and trash wedged between the Belt Parkway and Jamaica Bay, Plumb Beach has been a squatter’s haven, a prospective battery, a carnival grounds, a would-be battlefield, a gay cruising spot, and a windsurfers’ hangout. But throughout the seamy history of this ragged edge of Brooklyn, one population has remained consistent: the horseshoe crabs.

Every spring when tides are high under full and new moons, and an ancient alarm inside the crabs rings, thousands of them come ashore. Males hang like baubles, necklacing the larger females, and they spawn. Then they lurch back toward the surf, leaving their eggs to the shorebirds. Of the 100,000 eggs a female lays each season, three crabs will survive. It’s a vital feast for a ruddy bird called the red knot, which stops here on its flight to the Arctic. 

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That threatened bird, and the crab’s baby-blue blood, have led to intimacy between human and horseshoe. The crabs are great conch bait. They also are a biomedical necessity, for their blood clots in response to bacterial toxins. To create a contamination test used on vaccines, IV drugs, and medical devices, more than a half a million crabs are caught, bled, and released each year. To curb the bait fishery and leave crabs for the birds and biomedicine, quotas and monitoring were put in place. Now, East Coast states are counting their mating crabs. New York depends on volunteer teams to do the job: retirees; Audubon interns; and the stray, overworked New Yorker like me, looking for balance—redemption, really—in the moonlight, the lapping surf, and the age-old scrabble of impassioned creatures on the strand.

When tides are high under the full and new moons, an ancient alarm inside the crabs rings.

On June nights, I’d rush from my stressful job with its fantasy of profit, and in rubber boots, I’d pace the beach, throw down a rectangle made of PVC piping, and count the crabs framed within it. I’d maneuver calipers around the girth of a crab and call out its size. I’d drill a hole in a shell and pop a big, white label in; the tagged crabs looked like corsaged grooms, so oddball and vulnerable in their ardor that it was hard not to fall in love with them in turn.

I had thought them quotidian. In the summers of my childhood, the lagoons of Long Beach Island, New Jersey, were filled with horseshoes. They’d rear from opaque waters, so alien with their barnacled helmets, spiked abdomens, picketlike tails, and—when we found them belly up—bristled legs, dog-eared gills, and no meat to speak of. We gave them wide berth. 

Related: The Responsible Way To Collect Souvenirs From Nature

But vacation to vacation, coexisting with only shoreline between us, the crabs became not Jaws nor Moby Dick, but commonplace and so, to us kids, disappointing. At Plumb Beach, I learned that horseshoes’ averageness is their salvation. The animal is a generalist. It eats anything: algae, worms, clams. It doesn’t care how cold the water is, or how polluted. Seas rise and fall, continents break apart. But for nearly half a billion years, this insect of the seas, more spider than crab, has carried on. Like its namesake, it is lucky—if it has a beach. In Asia, horseshoes are threatened by habitat loss—a tragedy, since they aren’t picky. So long as the sand is well aerated and the slope gentle, a dirty spit of Brooklyn will do. 

Mating has its drawbacks. The surf can topple crabs. Top-heavy, legs scrabbling, they’re a meal for gulls then, or a sacrifice to next day’s sun. And therein lay my redemption. Horseshoe crabs have been called “living fossils.” Really, they’re survivors. They’ve been commonplace for 450 million years. But I was wrong as a kid: That’s opposite of disappointing; it’s an exhilarating track record. So when they tumbled, topsy-turvy, in the surf, we volunteers righted them, our tiny part, geologically speaking, in helping them lumber on for, hopefully, 450 million years more.