It was midnight, and we were freezing our buns off, poking in the tide for spawning Horseshoe Crabs.

We’d been in Delaware for two days of our week’s vacation in Bethany Beach, and I’d seen the ad that morning, hanging outside the gatehouse to Cape Henlopen State Park. “Volunteers wanted for Horseshoe Crab Census,” the poster said. An annual census, taken at high tide, during the full moon. During mating season.

We’d walked the beach the day before, and I’d seen a Horseshoe Crab carcass in the sand. I’d only ever seen them in pictures, and here was a real one—a shell, at least—looking ancient and creaky and remarkably like my old Army helmet. I was fascinated by the critter.

And now the ad had also piqued my more prurient interests: these things actually…mated??

I tried to picture it, but my best scenario amounted to a pile-up of Sherman tanks. The only hope I could see for romance between such clunky creatures was eHarmony.

So I called the number on the poster. And spoke to Rob Schroeder, an Americorps volunteer coordinator for Delaware State Parks. He was also a retired high school Biology teacher and, it turned out, a helluva nice guy.

Rob told us to be at the park at 11 p.m. “Dress warm,” he added.

**

We met Rob and a bright young Americorps volunteer named Bridget—who manned (womanned?) the park headquarters as her day-job—in the parking lot. He gave us each a red light to strap to our forehead.

I expected him to hand us bags and send us into the forest to hunt snipe. Instead, he explained that Horseshoe Crabs have lots of eyes (as many as 10, says one website: two large-ish compound eyes on the sides of the shell, two teensy ones near these, three small eyes on top, two underneath near the mouth, and a light sensor system on the tail that counts as one eye). Flip a bright white light on all this sensory equipment, and it’s like dumping cold water on a pair of lovers. Except that these lovers were already in cold water. And they didn’t travel in pairs.

It seemed that mating, for the Horseshoe Crabs, is even more bizarre than I’d imagined. The female is big, maybe two feet long including her spiny tail. Males run about two-thirds as large, and have a set of rounded claws, like small boxing gloves. The males lie in wait beneath the high tidewater in the dark of night; when they find a female, they latch onto her shell with these claws. Then it gets really kinky: more males latch on—four, five, six of them—and the female pulls them all like a mobile orgy over the beach. She digs in the sand as she travels and deposits eggs, and the males fertilize them as she drags them over the nests.

So this is what we were looking for as we set off, red lights at the ready, young Bridget toting a clipboard and pen.

**

Rob has helped with the annual census since the University of Delaware initiated it in 1990. There are a total of 25 participating beaches in Delaware and New Jersey. The census is held for three days each during the full and new moons in May and June, when the tide is at its highest level. During his total of 12 days, Rob presides over 100 square meters of Henlopen Park tideline. He chooses two square meters out of every ten, to get a representative sample, and counts the number of male and female crabs he finds.

We paced the shore, stopped at Ron’s sample areas, bent over the lapping tide waters, hovered our red lights, and called out what we saw so Bridget could jot it on her clipboard.

Square One: Nothing.

Two: Nothing.

Three: A crab. Dead.

Nothing. Another dead crab. Nothing.

Finally, at Square 14—a crab. One lonely, living crab. A male. Swimming by himself. Looking for love in all the wrong places.

He was the only Horseshoe Crab we counted all night.

**

It happens, said Rob. We were back in the parking lot; we’d returned our red lights and were rubbing our frozen hands together. It’s unseasonably cold, he said. It’s only May; the highest counts are usually June’s. It’s the end of the full-moon phase, not the highest point of the tide.

Still… he admitted that the numbers seemed to be decreasing over the past few years (Note: The 2008 census report agrees; it quotes a marked reduction in spawning numbers over a three-year span).

Maybe it’s predators, he said: birds, fishermen using crabmeat for bait. Pollution. Beachfront over-development… Labs also use the crab’s blue blood to test for human infections, but they return the animals after the bleeding, and most survive (one source estimates a fatality rate of less than 10 percent).

A decrease in numbers is bad news for migrating sea birds, Rob told us. They depend on crab eggs to survive. When times are good, there are plenty to go around—it’s thought that a sexually mature female (nine or ten years old) could lay more than 90,000 1/16-inch eggs a season, fewer than ten of which survive to adulthood—but lean times are tough. Fewer spawning crabs means less bird fodder. And, of course, fewer new crabs.

It’s a sobering scenario.

Here’s a creature that’s lumbered through life pretty much unchanged for 250 million years. If the gods are kind, it lives maybe 20 years, eating worms and clams. It’s a model citizen, donating blood for the betterment of mankind and laying out caviar banquets for Mr. Audubon’s best friends.

All it wants from us is a beachfront rental a couple nights a year to hold its funky but silent little frat parties. And when the whoopie’s done, you won’t find a single beer bottle on the sand.

What kind of neighbor would turn down that modest request?

**

To learn more about the Horseshoe Crab, including how you can volunteer for the yearly census, here are two terrific websites:

http://www.ocean.udel.edu/horseshoecrab/index.html

http://www.dnr.state.md.us/education/horseshoecrab/