Thursday, May 31, 2012

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.}


Jason H. said...

OK, I admit it, I am jealous!

Caroline Maun said...

I enjoyed this entire series on horseshoe crab mating. What a great adventure! And I did ask about satellite males when prompted recently. Oddly, I don't recollect their being featured on Mutual of Omaha's Wild Kingdom.... --Caroline

Olivia V. Ambrogio said...

It *was* a great adventure--I'd recommend it to everyone! And I'm glad you were able to enjoy it secondhand!

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