On Horseshoe Crab Mating: a haiku

One suitor clasping:

"Love is to cling!" One sidles:
"In subtlety, love."

For more on the mating behavior of horseshoe crabs, check out this post--and stay tuned for more about our most recent feats of horseshoe-crab voyeurism.

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More Merostomate Moments

From our horseshoe-crab weekend:

1. Not-so-wild-life meets wild-life:




2. Robin documents the return to the sea of a horseshoe crab we rescued (by turning it right-side up):



(there it goes:)







3. I rise before dawn to take photos of the sea, surf, and horseshoe-crab flotsam of the beach:



....And that's all I've got for you. It is Monday, after all.

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Time and Tides

[Do you break in your brand-new shoes by soaking them in seawater twice in one day because you misjudged the waves? Me too!]

This past Memorial Day weekend marked the second year that the Limulus Gang—Annie, six of our friends, and I—traveled to Lewes, DE for a weekend of lounging, beach-combing, and spying on mating horseshoe crabs. Because Annie and I also brought along our new(ish) dog, Earnestine, who has some anxiety issues around people who aren’t us, our peaceful weekend was regularly punctuated by panicked barking directed at friends she had only met 17 or 20 times (sorry, guys).



Nevertheless, it was a pleasant and fruitful trip, and the weekend luckily coincided with the full moon—the time of highest high tides—and thus the optimal situation for horseshoe crabs to feel romantic.



As you—as everyone—should already know, each year in late spring horseshoe crabs come ashore with the evening high tides to mate: males clasp onto females, who burrow into the damp sand and release their eggs, which are then fertilized by the clasping male and, potentially, by “satellite males” that cluster around the mating pair. Delaware Bay hosts the largest concentration of these ancient-looking arthropods, and it just so happens that their peak spawning occurs near Memorial Day.



Friday was cold and blustery and full of rain, but Saturday night was clear and calm: the perfect weather for arthropod voyeurism.

Last year (our first year as marine peeping Toms) we had seen a decent number of horseshoe crabs dotting the beach. This year, they were everywhere. And, while last year some of them shied away from our flashlights, this year they were too taken with the thrill of their moment(s) of intimacy to pay us any attention.



They were present en masse, with some areas of the sand carpeted with huge groups of lustful invertebrates. In fact, it was rare to see a mating pair without a retinue of satellite hangers-on—and the arthropods were so intent upon their orgiastic activities that separate mating groups would sometimes plow into one another.





I took a good number of photos (say, 100 or so) of the animals while my fellow Limulus Gang members obligingly trained flashlights on the seething mass of mating merostomates—but we weren’t only oglers: we had a higher purpose.

Often horseshoe crabs coming to shore will be flipped over by the waves, and if they’re unable to right themselves, they’re doomed to be abandoned by the tides and left to die a desiccated death.



Like the heroes of old, we stepped in, turning over the struggling creatures to let them mate again another day. We even developed a streamlined technique for tilting them by their carapace (avoiding their fragile tails!) so that they sensed the movement and were able to smoothly finish the job themselves—thus giving them a sense of agency as well as a new lease on life.



The rest of the weekend was spent in typical beach-house fashion: eating potato salad and hot dogs, drinking, watching Barbarella, discussing the possible religious beliefs of dinosaurs’ intelligent descendants had the asteroid not hit, etc.

For me, though, there was a certain melancholy element to the weekend, even amidst the revelry. For one thing, vacation time always passes twice as quickly as normal time, so even as you enjoy it you know just how fleeting it is.

For another, one of the gang will be moving to Massachusetts this fall, and the knowledge of that move cast a shadow on the proceedings, a reminder that all things change. They have to, of course, and much as we’ll miss her, we’ll wish her the best, and hope to have her join us next year at the beach. But… it won’t be the same. What will?

That’s why I’m especially grateful that we were able to witness and document this ritual of renewal under the full moon, reminding us of what persists even as it alters. And as summer’s swelter gives way to fall, and the dark nights of winter, and the fresh sap of spring, I’ll be able to remember the part we played in the ritual, rescuing its participants so that they could return for another year, and another year, and another after that.

{A note: I do write all text and take all pictures. Please do not reproduce either without my permission.}

How We Spent Memorial Day Weekend

(Adventures in Arthropod Voyeurism Part 2)

[carapace of a lady crab (a species, not an epithet)
on the porch of the house we rented in DE]

At midnight on Friday, six members of the Limulus gang (those who weren’t either asleep or still in transit) walked the block and a half from the house we’d rented down to the beach. It was a clear night and the sky was scattered with a profusion of stars—a sight so mesmerizing to us city-dwellers that several members of our party nearly ran into trees, parked cars, and other roadside obstacles as they attempted to walk while gazing up at the heavens.

In spite of these dangers, we reached the beach without incident and stumbled along the uneven sand to the water, which we could hear more than see. We were guided in our trek by the light from some beach partiers’ bonfire; the young men and women gathered around the flames watched us curiously as we made our way to the shoreline and, using a crank-powered flashlight and the “flashlight app” on Annie’s phone, swept the beach with their beams.

There were no horseshoe crabs.

We walked further down the beach, moving our lights back and forth over the wet sand, and still found nothing.

“Maybe it’s too late in the season after all,” I concluded resignedly. “Well, we can at least enjoy the stars.”

We stood with our feet lapped by waves and stared up at the sequined dome of sky.

And then a different light source caught our attention. Two figures—mere silhouettes—were jogging down the beach, powerful flashlights and miner’s lights bobbing with their steps. As they got closer, we could make out a man and his ten-year-old son (he was the one with the miner’s headlamp) moving rapidly along the shore.

They too, it turned out, were looking for horseshoe crabs—but unlike us, they had found them: shining their powerful beams into the surf, they pointed out the shield-shaped shadows just beneath the surface.

[there are three horseshoe crabs in this picture;
can you find them all?]

We had arrived on the beach before the horseshoe crabs, but the crabs were coming, too.

They didn’t come en masse, as I had hoped they would and as they probably had done during the peak of the season. Nonetheless, gradually we could make out more and more of them in the shallow waves near shore—some already locked in a precopulatory embrace.

Soon we learned to recognize the shadows in the waves and the faintest hints of curved shapes breaking the smooth line of sand, and we’d cry out and run for them, much like sailors on whaling ships scanning the horizon for spouts (but less bloodthirsty).

At first the horseshoe crabs were shy of our lights, veering away from portions of the shore that we illuminated and making us feel a bit like police officers spotlighting parking couples:

We discovered, however, that once they had gotten onshore and the female had entrenched herself, we could gawk at them to our hearts’ content; they had more important things to focus on.

(We weren’t just peeping Toms, either: when one horseshoe crab got flipped upside-down by the tide and lay, helpless, on the sand, we did what you’re supposed to do and gave it a hand, turning it right-side up—but making sure not to touch its fragile tail, or “telson”.)

We saw several mating and pre-mating pairs spooning in the sand:

We also saw satellite males approaching and joining the mating action! (For more information on what satellite males are—although the name and photos should tell it all—see this post.)

[mated pair with approaching satellite]

[mating pair with two--count 'em, two!--
satellite males; note how much bigger
the female, partly submerged in sand,
is than the males]

Just to be clear: I may have been the one who thought up this adventure and provided the initial enthusiasm—and I was certainly the one who wrote up a fact sheet and made buttons—but I was not the only one who was excited by these sightings, not by a long shot.

Annie and our friends exclaimed just as loudly as I did, stared just as avidly into the waves to spot approaching individuals, and, even more fascinated than I, bent, rapt, over the gleaming armored shells of the amorous arthropods.

[our friend is shining a flashlight on the
horseshoe crabs--but doesn't it look like
she's interviewing them?]

This is not to say that all human visitors to the beach were equally thrilled with the invertebrate party going on. The group sitting around the bonfire had been blissfully ignorant of the momentous season during which they had chosen to camp on the beach, and once the man and his son, with their powerful flashlights, had shown them that the waves were alive (with the sight of crab-sex), their excitement was doused as swiftly and surely as their bonfire. By the time we got back to that portion of the beach, nothing was left of the group but a pile of sand covering the former fire-pit. Once again, the shore was ceded to invertebrates.

In the end, we couldn’t last much past 1:30am (although the horseshoe crabs certainly could). We wandered back home, bleary but smiling, and fell into bed with visions of merostomates dancing in our heads.

What more can I say? It was the best Memorial Day weekend ever.

{A note: I do write all text and take all pictures. Please do not reproduce either without my permission.}

A Gripping Tale: Strong Embraces and Hangers On

(Memorial Day Arthropod Voyeurism Part 1)

[the button I had made for all 10 of us
in "The Limulus Gang"]

During the horseshoe crabs’ lustful storming of the Delaware beaches during May’s high tides, it’s all about sex—but not always in the same way.

For horseshoe crabs, fertilization is external but still close-up and personal—none of that soulless, faceless broadcast spawning for these invertebrates, thank you very much. Instead, a male grips a female—either before or soon after she’s crawled on shore—and, while she releases eggs into a nest she’s dug in the wet sand at the water’s edge, he releases sperm over them.

All well and good, and very romantic—a midnight embrace on the starlit shore, the waves murmuring sweet nothings—but that’s not the only kind of hanky-panky going on. Some males don’t compete to grip females; instead, they hover around already mated pairs, clustering close, and also release sperm over the female’s eggs.

These males are called “satellite males,” and—although the number of eggs they fertilize varies a lot—they still end up with enough offspring from their sideways encounters that their tactic is considered a legitimate alternate mating strategy.

And it really is a separate strategy, not just a back-up plan for those males too slow or shy to find a solo female; I’ll have to check my sources to provide you with citations, but I’m pretty sure researchers have found that the same males remain either satellites or grippers (not the technical term) at different times and under different circumstances.

You have to admit, this adds a whole new level of coolness to the whole spawning event. Think of it: a massive group mating that rivals even the worst excesses of ancient Rome or the 1970s, happening right here on the beaches, reminding us of the magnificent diversity and perversion of the animal world! (And I mean that in the very best way possible.)

And did we see it happen?

All will be revealed in the next installment of Arthropod Voyeurship!

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Did We or Didn’t We?

This Memorial Day weekend, 10 of us came together on the shores of Lewes, DE, our only desire to observe the mating rituals of spawning horseshoe crabs (and, okay, to enjoy a beach vacation in each other’s company, but that was really peripheral).

But horseshoe-crab mating peaked early this year, and the evening tides this past weekend were weak, neap tides at midnight and 1am. Were the horseshoe crabs still tugged shorewards by their burning desire to mate—and if so, did we see them?

And either way, why should you care about the private lives of ancient-looking arthropods?

Stay tuned to learn the answers to all of these questions—and more!

{A note: I do write all text and take all pictures. Please do not reproduce either without my permission.}

Shore Thing

In a world wracked with chaos and uncertainty, it’s nice to know that there’s at least one thing you can count on: each May, as the days lengthen and the waters warm, the horseshoe crabs emerge from the deep waters off of Delaware Bay and, pulled with the highest new- and full-moon tides, gather on the beaches in a seething wave of lust to propagate the next generation of bizarrely shaped arthropods.

It just gives you a warm, fuzzy feeling, doesn’t it?

I’ve known about this yearly ritual for quite some time—ever since I did a literature review on horseshoe crabs back in college—but this is the first year that I will be present for it. This in spite of the fact that Annie and I have been here in DC, just a few short hours from the Delaware Bay, for two years now! It’s embarrassing, how long it took me to put two and two together…

But there’s no point brooding on the past—for this year, this Memorial Day weekend, Annie and I and six of our friends (and my parents) will descend upon Lewes, DE, and spend the weekend being Limulus polyphemus voyeurs!

Well, some of us more than others. I have a sneaking suspicion that at least some members of the party are more interested in spending the weekend at the beach (or watching DVDs in company) than they are in observing this once-a-year mating event. But I can live with that, especially since I intend to discourse extensively on horseshoe crabs regardless of the level of enthusiasm of my audience (I’ve even made a fact sheet).

In fact, the only thing I’m actually concerned about is that we’ll have missed the peak of horseshoe-crab mating—which, like every other seasonal event this year, occurred weeks earlier than usual. Still, there should be a fair number of stragglers still swarming the beaches, like late-comers to a party.

We should also get to see a good number of the migratory shorebirds that depend on the beach-laid horseshoe crab eggs for fuel during their long flights to the Arctic. So look forward to hearing about more absurd-but-true shorebird names in the weeks ahead! (Yes, they really are called “dunlins.”)

[actually, these are willets]

And you can definitely expect another post describing the fascinating sex lives of horseshoe crabs. (There will be citations. There may even be illustrations.)

All in all, it should be a pretty great Memorial Day weekend. I can only hope that all of you have equally exciting plans.

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Wild Wildlife of Delaware, Part II: Unguarded Beaches, Discarded Armor, and Abandoned Waves

[lacy, whelk shell pierced with light]

Near Rehoboth Beach, in Lewes, DE, is Cape Henlopen State Park, site of beautiful beaches, woods, and ponds, as well as sand roads that should only be driven on by large all-terrain vehicles (trust me on this). We spent a lot of time at one of these beaches, lying in the sun like animals and taking long walks.


The beach was strewn with bits of horseshoe-crab carapaces. Horseshoe crabs, as you may know, are not actually crabs at all; in fact, they’re more closely related to spiders and mites. Relatives of contemporary horseshoe crabs, with much the same body plan, have been around for millions of years—hence the reference to these non-crabs as “living fossils,” even though they themselves haven’t been around quite so long.

[horseshoe-crab leg and shadow]

Horseshoe crabs are important not just in and of themselves but because they’re important bait species; they’re used in biomedical research; and their eggs, which they lay on the beach, are the major food source for a huge number of migrating-bird species. (Also, some really interesting work has been done on horseshoe-crab mate recognition and mating behavior—see Professor H. Jane Brockmann’s website for more information on some of this research.) It was too late in the year for us to see any live horseshoe crabs wandering around mating, but there were a few full carapaces as well as pieces on the beach, lying there like armor thrown off following a campaign:


There were some gulls on the beaches, as well, although—perhaps because this beach was less populated by humans and their foodstuff—not a large number of them. A few strutted the shores or had recently done so:


But the majority of them were either off at sea or visible only in the distance as a multi-species group whose members suddenly all took off at once in response to some signal unperceived by us.

We spied some other shorebirds as well, and to spare you the suspense that’s no doubt been building since I mentioned them last, I’ll tell you what kind they were: willets! (I’m convinced that all shorebirds are required to have bizarre names, like willet or dunlin or dowitcher or curlew or whimbrel or godwit.)


They hurried on ungainly, stilt legs to and fro along the shore, plunging their dark beaks into the sand to catch mole crabs and other hapless crustaceans and mollusks that hadn’t burrowed quite deep enough.


Apart from the wildlife (which, I admit, I was considerably more interested in than was Annie), we enjoyed being in the presence of the ocean itself. We delighted in the furiously pounding surf and in the wild foam that came racing up the shore in the wake of each crashing wave, a delirious effervescence rich as the froth bubbling up from a just-opened bottle of champagne—and just as intoxicating. It was as if the sea itself were, with each intermingling spurt of spray, making a display of its exuberance.


Some of the effect was due, too, to the quality of the late-afternoon light, which softens and enriches tones and colors and maybe even moods. In the mid-morning, by contrast, the waves that spilled over the beach were hit by a hard, direct light, like a hammer beating thin a sheet of metal: and then the shore looked as if it were being washed with successive layers of silver.


And thus concludes my abbreviated travelogue of our weekend trip to the wilds of Delaware. We’ll probably go again, and I’ll be furnished with more stories and photographs to share. Maybe we’ll even go in late spring, when the horseshoe crabs are mating! Oh, imagine all the opportunities for X-rated-arthropod entries…!

{A note: I do write all text and take all pictures. Please do not reproduce either without my permission.}