Picture, if you will, the ragged shoreline of a secluded bay bathed in the light of a full May moon. It is nearing high tide and midnight, and there is a stirring along the water’s edge. Gazing down, you see a rounded shape, no larger than a small saucepan lid, dart from the shadows. At first glance, your creature resembles a shallow German World War II helmet (think Sergeant Schultz on Hogan’s Heroes), except with a hinge in its back and a swordlike tail. Covered with points and spines, it looks like an ancient fighting machine, a prehistoric tank — something that could do you great harm if you lingered.

One by one, these strange creatures clamber to the shore, their claws clacking on the rocks, some piggybacking others, as they search for a place to burrow into the mud and sand. Soon, their numbers grow by the dozens, until it seems there are hundreds of them surrounding you, clacking and clamoring. What to do? Flee? Fight? Faint?

The answer is none of the above, if you happen to be one of the select horseshoe crab enthusiasts who bear witness to this ritual that takes place at Taunton Bay on the Down East coast of Maine each spring. Instead, you lean in and gawk in awe.

The occasion is the two-week spawning cycle of the horseshoe crab. The significance of Taunton Bay, a six-mile, C-shaped stretch of tidal water located just east of Ellsworth, is that it’s believed to be the horseshoe crabs’ northernmost breeding habitat, which spans south to the Yucatan. That fact is something that puts Maine, and this oft-maligned and little-understood creature, on the map.

If you think I’m overstating the horseshoe crab’s case, let’s start with this: Did you know that the horseshoe crab is not a crab at all but is more closely related to spiders, ticks, and scorpions? And that this “living fossil” has survived — nearly unchanged — for 445 million years? And that its copper-based blood, which is blue in color, is valuable in pharmaceutical testing? And that despite all its aggressive-looking armature, these little critters are no more harmful than a ladybug, which, by the way, will actually bite you, whereas a horseshoe crab will not?

No, neither did I — that is, not until I was invited to view this spectacle and have my mind changed about these creatures forever.

You see, I grew up on the midcoast of Maine, where the sight of horseshoe crabs was not unusual, but it was nothing short of terrifying. Their presence sent us kids screaming from the water to hop from foot to foot on the beach, shrieking for some adult to come rescue us. Occasionally, one of us would be brazen enough to drag one of these monsters up on the beach and flip it over on its back, its weird machinery clawing at the air. Stranded, it would try to right itself by prodding its pointy tail into the sand, buckling its hinged shell open and closed, and trying to flip itself over. We would stand back in mesmerized horror.

Since that time, I had given little thought to horseshoe crabs, until I heard about their spring mating ritual through Down East Audubon and the Friends of Taunton Bay (FTB), a group dedicated to the health of the bay’s ecosystem. When I was invited to a special midnight, full-moon viewing by one of its members, I jumped at the chance.

I am the guest of Frank Dorsey, a semi-retired bio-statistician, and his wife, Mary Beth, a retired children’s librarian, who have a shorefront home on Taunton Bay. As I approach their warmly lit house, any doubts I might not be at the right place are stilled by the sight of silhouetted cutouts of horseshoe crabs decorating their front and side screen doors. I’m clearly in horseshoe territory.

Dorsey, a genial, lanky man wearing wire-frame glasses, greets me and gets right to horseshoe talk. With various carapaces spread before us on his dining-room table, we examine their anatomy. A horseshoe crab, he explains, is an invertebrate that grows by shedding. Its shell, which is made from a cellulose-like material called chitin, has three sections: the prosoma (or cephalothorax), which houses the intestinal tracts, as well as the nervous and the circulatory systems; the opisthosoma (or abdomen), where its “book” gills, which also serve as paddles, are located; and the telson, or tail, which is used for steering and righting itself if some little twerp upends it. Its mouth is located between its set of five legs in the front. As the legs move, food — worms and small shellfish — is crushed and guided into its mouth. “If they’re not moving, they’re not feeding,” he says.

Dorsey explains that Friends of Taunton Bay, which was formed in the 1990s, really got interested in the horseshoes when the Route 1 bridge at Sullivan was replaced in 1999. Shellfish draggers couldn’t pass under the former bridge into the bay but could clear the new one. To some, that posed a potential threat to the horseshoes. That’s when the scientific research began in earnest.

In 2001, the organization hired biologist Sue Schaller, who had been tagging and tracking the horseshoes, to conduct a survey. In 2003, FTB partnered with the Department of Marine Resources and began a survey of the horseshoes’ activity using sonar tracking. Twenty-six of the animals were rigged with transmitters to follow their movement.

According to FTB President Steve Perrin, who worked on the survey, they expected the horseshoes would head out of Taunton Bay as winter approached. Instead, it was discovered that these critters do not migrate (like their more southern counterparts do); they just travel a mile or so out into the channels of the bay and burrow into the mud for the winter. (Schaller did subsequent sonar tracking that corroborated this finding.)

Protecting that environment, says Perrin, became vital. “Because this is an isolated sub-population on the outer edge of its habitat, it is already fragile and vulnerable.” He says he is not opposed to mussel dragging if it is “suitably done within predesignated safe areas” and does not encroach on eelgrass meadows or horseshoe crab habitat. Several bans were put in place after the new bridge was completed but were lifted in 2008, when these “safe areas” for dragging were established. FTB will continue to monitor all dragging activity to ensure it doesn’t stress an already stressed population.

With a little background now under our belt, Dorsey suggests we head out to the shore in order to get a lay of the land before nightfall. On the point where his property is located, evidence of the area’s boatbuilding past can be seen: remains of ships’ ways and pier stones litter the water. As we pick our way over the rocks, gravel, mud, sand, and around the rockweed, Dorsey continues to share horseshoe lore with me. He explains the female is generally one third larger than the males, and that the males have what he calls a “boxing glove,” or front pincer claw, used to, well, muckle onto the female from behind, waiting for the moment he can fertilize her eggs. It takes about ten years for the males to reachoptimal mating size, and females eleven. They have two compound eyes on either side of their shell and thirty-six light sensors covering their body and tail, including one large rudimentary “eye” in the middle of their forehead. (Their Latin name, Limulus polyphemus, means “one-eyed giant.”) Their eyesight is so poor, says Dorsey, they are basically “legally blind” and can only make out forms. Anything that is rounded and vaguely resembles the shape of another horseshoe — a rock, a piece of wood, a boot — is a potential love mate for a male. The females are focused solely on finding a suitable spot for laying their eggs.

Dorsey and I pick our way over uneven terrain, stepping from rock to rock, feeling for sinkholes in the calf-high eelgrass, where some of the females will dig to lay their eggs — “no small job,” he says. We pause to watch a pink full moon wobble up over the horizon. It is around 8:30, and it will be at least a couple more hours before the tide and the horseshoe crabs arrive.

Of course, they are not really crabs at all, a fact I later learn from Sue Schaller who has been keeping an eye on these Taunton creatures, largely in a volunteer capacity, for over decade.

“I call them horseshoes, I call them animals or critters, but I do not call them crabs — especially in print — because they are not.”

In response to the assertions that Taunton is their northernmost habitat, that they don’t leave the bay — she responds with a scientist’s reserve. She says research supports these ideas. When the water cools in the fall, horseshoes start to “close up shop.” By the time the water temperature falls below ten degrees Celsius, they “remain confined to quarters,” meaning they are in their hibernating mode. Then, in the springtime, as the water warms, they yawn and stretch and move upstream to shallow water and hang out. Spawning is then triggered by a confluence of weather, water temperatures (thirteen or fourteen degrees Celsius), the lunar phase, and tides — usually sometime in late May or early June.

The horseshoes lay their eggs at the highest daily tide, so long as it occurs between 1 a.m. and 1 p.m. and is not a spring tide. (Many people think the term spring tide means a tide that takes place in spring — a common misconception, according to Schaller. It is simply the highest tide of any given month.) But the horseshoes don’t like a spring tide, because their exposed eggs will be dried out above the high-water mark. They also like a stretch of nice weather. “Everyone knows you don’t go looking for a mate at the beach on a rainy day,” she says.

So, the males loiter just below the high-water line, waiting for a prospective female to go by. If all the stars align, he’ll find a female and latch on, wait for her to release her eggs, and then “cast his blessings” (Schaller’s terms), thus perpetuating this 445-million life cycle.

It is nearing midnight on Taunton Bay. Dorsey and I are about to be nearly knee-deep in this ancient phenomenon. Although Schaller says the full-moon element to the spawning cue is myth, it certainly makes for an appealing backdrop. As darkness descends and the tide creeps in, Dorsey and I make our way out to Shipyard Point, clad in wellies and anoraks and armed up with headlamps and Maglites. We emerge from a thicket onto the beach and are instantly swarmed by mosquitoes. Dorsey dons a hood of netting and moves on unfazed. He’s clearly been through this drill before. I am trying my best to ignore the onslaught by casually waving away the pests with my notebook. And then, miraculously, we round the point, the wind picks up, and there’s not a mosquito in sight. Despite a stretch of warm days, the evening’s damp air cuts right through all my fleece and Gore-Tex, and I am chilled straight through.

Dorsey and I begin carefully picking our way along the rocks and wading into the shallows. The moon has climbed into the sky, spilling its beam across the coming tide and mud flats, like a spotlight awaiting the stars of the show, who are slow to take the stage. We walk, we peer into the water, we wait.

Then I see a ruffling of weed, a fluttering like a pom-pom, and suddenly a male darts out from under it. He skims quickly under the water’s surface, occasionally dancing on the sand beneath him. Dorsey explains that horseshoes are remarkably fast and agile swimmers, and he’s right. For such an ungainly looking creature, this guy’s moves are almost balletic as he glides and turns. He has mutton chops of bright green sea lettuce that waft in the water as he swims toward his target: a barnacled female. He mounts and clamps, and the two shuffle off along the water’s edge, giving a whole new meaning to the expression “hooking up.”

From there, things gets active. More and more males and females line the small arc of shore we have carved out for ourselves — not the two-to-five hundred (individuals’ counts vary) I had hoped for; it is, after all, toward the end of the season — but a good few dozen. As I follow their movements, I can see the horseshoes prefer to move up the channels and grooves created by the tide. Dorsey points out a male in hot pursuit of a female, and we watch him catch up and clamp on. Not long after, another male joins the Conga line. With thousands of eggs per female, I guess there are plenty of “blessings” to go around.
 
Just as we’re getting ready to wrap up, a smaller horseshoe (a male, I presume) advances toward my boot. I neither flee nor faint, but watch to see what he’ll do. Sure enough, that rounded toe must’ve given him what appeared to be a come-hither look, because the next thing I know, he’s mounted my wellie. I endure it as long as I can, but in my child’s imagination, I swear I can feel those claws clamoring through my boot. I gently slide my foot away (letting the suitor down gently) and make haste to the shore. As I do, Dorsey — perhaps in a show of male solidarity — steps in and substitutes the toe of his boot for mine.

Soon, the fellow will realize his mistake, slip from Dorsey’s boot, and grope his way along the ocean floor, following the call his ancestors have been heeding for time immemorial. As long as the horseshoes remains healthy and vital, he needn’t rush. Because, if there’s one thing these ancient creatures have on their side, it’s staying power.