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What Do Snails Think About When Having Sex?

It starts with a light, soft touch, one tentacle gently reaching out, hesitant, hopeful, hanging lightly in the air. There’s a pause. Skin touches skin. One softly strokes the other and slides closer, and then, carefully, they wrap themselves together, stroking, probing, entwining. They glisten as they move, and because they are snails, everything happens very slowly. The rubbing, the rapture, the intensity of it all—snail sex is extraordinarily lovely to look at. (If you aren’t at your office desk or on a train where people can see your screen, I’ve got one about a garden snail named Chip who’s trying to lose his virginity, or take a quick peek—30 seconds will do—of this coupling in a garden.)

Lovely but So Dangerous

Garden snails make love in the open—on garden patios, in clearings on the forest floor—and they do it luxuriantly for one, two, three hours at a time, under the sky, where they can be seen by jays, orioles, frogs, snakes, shrews, mice, beetles, and other animals that might want to eat them. Snails can’t make quick getaways, so exposing themselves like this is dangerous, crazily dangerous. What’s going on? What’s making them so impervious, so deeply preoccupied with each other? Here’s one answer: Snail sex is very complicated. Snails have a lot to think about when they make love—because they’re hermaphrodites.

Unlike you, garden snails can produce sperm like males and carry eggs like females at the same time.

Drawing of a proud snail, with its hands on its shell hips
Drawing by Robert Krulwich
Drawing by Robert Krulwich

Which is both an advantage and a problem. Professor David George Haskell, a Tennessee biologist, once squatted down on a patch of forest floor and watched what you just saw in that video—a snail couple going at it—except with a magnifying glass and only a few feet from the action. What he noticed was their mood. Hot as it was, he writes in his book The Forest Unseen, “Their extended courtship and copulation is choreographed like cautious diplomacy.” Snails don’t pounce, they circle. They “slowly edge into position, always ready to pull back or realign.” Their sex is tense, charged, on, off, then on again, “a prenuptial conference over the terms of the union.” What are they negotiating about?

In most animals, snails included, sperm is plentiful, cheap to produce, and fun to unload. So one presumes that both copulating snails are eager to get that part done.

A drawing of two snails, both looking at each other with thought bubble exclamation points above their heads
Drawing by Robert Krulwich
Drawing by Robert Krulwich

Eggs, on the other hand, are limited and hard to produce—and therefore precious. You don’t let just anybody fertilize your egg sack. So, in Haskell’s imagination, if one of these snails picks up “a whiff of disease” on the other, it may be happy to poke but is not at all interested in being poked. No one wants its precious eggs fertilized by a sick dad, so the receiving snail might lock its partner out of its opening while also trying to penetrate it. This could produce feelings of frustration, confusion, and even unfairness in the other.

A drawing of two snails looking at each other, one with an exclamation mark thought bubble and one with an X through an exclamation mark thought bubble
Drawing by Robert Krulwich
Drawing by Robert Krulwich

“In hermaphrodites,” writes Haskell, “mating becomes fraught, with each individual being cautious about receiving sperm while simultaneously trying to inseminate its partner.” Sexually speaking, two snails with four minds—a foursome in a twosome—makes for complex fornication. That’s why snails are always on tiptoe, Haskell thought as he watched them on the forest floor: They have so much to figure out.

Picture of a brown snail peering its head around to the side
Photograph by © Tetra Images / Alamy
Photograph by © Tetra Images / Alamy

Hermaphrodite Abundance

So why be a hermaphrodite? Are there a lot of them? Well, here’s a surprise: They’re everywhere.

Eighty percent of the plant kingdom produces both seeds (pollen) and eggs (ovules) and can give or receive, making them hermaphroditic. They’ve learned that when the weather gets wet or cold, bees can’t be depended upon to buzz by and pollinate, so they have a we-can-do-this-ourselves backup plan.

Animals, generally speaking, are sexual, divided into male and female. But, writes Stanford biology professor Joan Roughgarden in her book The Genial Gene, if you subtract insects, which make up more than 75 percent of the animal kingdom and are not hermaphrodites, we are left, she calculates, “ … with a figure of 1/3 hermaphrodite species among all animal species.” That’s a hunk of hermaphrodites.

So Who’s a Hermaphrodite?

They’re not animals we pay much attention to (flukes, flatworms, killifish, parrot fish, moray eels, barnacles, slugs, earthworms, and tapeworms, among many others), but they are switch-hitters: They can either give or receive or switch sides during their lifetime. “All in all,” writes Roughgarden, “across all the plants and animals combined, the number of species that are hermaphroditic is more-or-less tied with the number who has separate males and females, and neither arrangement of sexual packaging can be viewed as the ‘norm.’”

Anyone who thinks that male/female is nature’s preference isn’t looking at nature, says Roughgarden. And she goes further.

Adam and Eve or AdamEve?

She wonders, Which came first, the hermaphrodite or the male/female? We have lived so long with the Adam and Eve story—Adam first, Adam alone, Adam seeking a mate, God providing Eve—that the question seems almost silly: Of course complex animals started with males and females.

Painting of Adam and Eve in the Garden of Eden, Eve is offering Adam an apple
Adam and Eve, 1537 (panel), Cranach, Lucas, the Elder (1472-1553) / Kunsthistorisches Museum, Vienna, Austria / Bridgeman Images
Adam and Eve, 1537 (panel), Cranach, Lucas, the Elder (1472-1553) / Kunsthistorisches Museum, Vienna, Austria / Bridgeman Images

But Roughgarden wonders if animals started as hermaphrodites …

Composite of Adam and Eve painting, creating one person
Composite image of Adam and Eve created by Becky Harlan from original paintings by Lucas Cranach © [Royal Museums of Fine Arts of Belgium, Brussels / photo : Guy Cussac, Brussels]
Composite image of Adam and Eve created by Becky Harlan from original paintings by Lucas Cranach © [Royal Museums of Fine Arts of Belgium, Brussels / photo : Guy Cussac, Brussels]

… and then “hermaphrodite bodies disarticulate[d] into separate male and female bodies?” How would that have happened? Roughgarden cites a paper she did with her colleague Priya Iyer.

They propose that maybe the earliest animals started out as both sperm and egg carriers, and a subgroup got especially good at inserting their penises into enclosures, aiming, and directing the sperm to its target (the authors call it “home delivery”). They did this so effectively that they needed fewer and fewer eggs and essentially became sperm sharpshooters or, as we call them now, “males.”

That development gave others a chance to give up sperm altogether to concentrate on chambering their eggs in nurturing nooks, thereby becoming “females,” and so more and more animals found it advantageous to be gendered.

Ayer and Roughgarden aren’t sure this happened. They say that, on available evidence, the story can go “in either direction.”

The alternate view is almost the story you know. It’s Adam and Eve, with a twist: In the beginning, early animals were gendered—except when it was inconvenient.

If, for example, you imagine a group of, well, let’s make them snails …

Drawing of a group of snails standing in front of a volcano erupting
Drawing by Robert Krulwich
Drawing by Robert Krulwich

… and something awful happens—there’s a terrible disease, an ice age, a new ferocious predator, or maybe a volcanic eruption…..

Drawing of a snail all alone after the fallout of a volcanic eruption, standing in front of a volcano puffing smoke
Drawing by Robert Krulwich
Drawing by Robert Krulwich

… so that we’re left looking at a lone individual, all by itself, looking around for a reproductive opportunity, crawling across the landscape, hoping to bump into somebody, anybody, to reproduce with, and after a long, long, anxious period, it finally sees what it’s been looking for. It crawls closer, closer, the excitement building.

Drawing of a snail in a vast and sunny landscape seeing another tiny snail in the distance
Drawing by Robert Krulwich
Drawing by Robert Krulwich

But as it gets within wooing range, it suddenly sees that—oh, no—it’s the same gender!

A drawing of two snails with moustaches
Drawing by Robert Krulwich
Drawing by Robert Krulwich

No possibility of babymaking here. And this happens half of the time. (Statistically, that’s the likelihood.) Now instead of being your friend, male/femaleness is your enemy. What wouldn’t you give for a hermaphrodite, a he/she snail that could, in a pinch, be whatever sex you need it to be. With a hermaphrodite, you can (again statistically) always make a baby. What a relief. So maybe that’s what happened. Gender difference disappears when gender no longer helps produce more babies (and when you don’t have to stick around and be a parent).

Which is the true story? We don’t know. Maybe the only story is that nature is flexible. When gender is useful, you get genders. When not, you don’t. What we forget, being humans, is that there are so many ways to flirt, to combine, to make babies—and the world is full of wildly different ways to woo. Tony Hoagland knows this. He’s not a scientist but a poet who lives in New Mexico, and in his poem entitled “Romantic Moment,” he imagines a boy on a date who sits next to his girl imagining … How shall I put this? … how the Other Guys do it.

Romantic Moment by Tony Hoagland

After the nature documentary we walk down,
into the plaza of art galleries and high end clothing stores

where the mock orange is fragrant in the summer night
and the smooth adobe walls glow fleshlike in the dark.

It is just our second date, and we sit down on a rock,
holding hands, not looking at each other,

and if I were a bull penguin right now I would lean over
and vomit softly into the mouth of my beloved

and if I were a peacock I’d flex my gluteal muscles to
erect and spread the quills of my cinemax tail.

If she were a female walkingstick bug she might
insert her hypodermic proboscis delicately into my neck

and inject me with a rich hormonal sedative
before attaching her egg sac to my thoracic undercarriage,

and if I were a young chimpanzee I would break off a nearby tree limb
and smash all the windows in the plaza jewelry stores.

And if she was a Brazilian leopard frog she would wrap her impressive
tongue three times around my right thigh and

pummel me lightly against the surface of our pond
and I would know her feelings were sincere.

Instead we sit awhile in silence, until
she remarks that in the relative context of tortoises and iguanas,

human males seem to be actually rather expressive.
And I say that female crocodiles really don’t receive

enough credit for their gentleness.
Then she suggests that it is time for us to go

to get some ice cream cones and eat them.

Thanks to the poet Thomas Dooley for suggesting Tony Hoagland’s poem, and to Mr. Hoagland for giving us permission to print it here in full. Reading “Romantic Moment” I giggled a little to think of eating ice cream on a sugar cone as a homo sapien mating ritual—but thinking back, I think he’s onto something. The poem can be found in Tony Hoagland’s collection Hard Rain.