Snail Sex Tape

Okay. Alright. Okay. Alright. Here we go.

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Radio from... WNYC. You see? Yep. M.I. recording.

I'm recording.

“Do you, does your mic have fancy green lights on me?”

Does yours not? No. It, like, tells me how loud it is. And it also, I can also mute it. Can you hear me?

Can you hear me? You can't hear me anywhere. No, I can't. You can't? Yeah.

Wait. What does that button mean then? Button. Button. I'm Molly Webster.

This is Radio Lab. Button. Button. Okay.

And today, I am joined by our executive editor.

Button. Soren Wheeler. What are we doing? Why are you here? Well, you're here because I'm going to take you on a walk.

Oh, you're going to take me on a walk. Where?

“In a lowland area along the Kinabataang River.”

We're going to follow this guy, Menno. He's an evolutionary biologist. Seems like a nice guy to go on a walk with. Menno is going to take us deep into Borneo. It's tropical humid limestone forest.

So it's really wet. There's like in there's ferns. Or kids and vines and climbers. And he is looking for something. Okay.

And actually, Papa Pie also went on a walk to look for something. Oh, my walk was not Borneo. It was in Brooklyn. In February. So less orchid don't poop more cigarettes trash. Here's a pigeon. So this is something that you can find in both Borneo and Brooklyn.

Yes. In Borneo, it's down by the river banks. And the limestone cliffs in Brooklyn. Oh, no. I'm right here. You just make your way through one single door to a store. And then right there, there's a glass tank.

Using my face up against the glass. Really put my face to the surface of the rock. And then glistening in the sun. Oh, my goodness. I see these miniature tiny, tiny.

Snales. Snales. A little brown shell with squirrels. Is the thing that we went on a walk to see. Right.

Got two little antennas. And I just can't imagine a penis coming out of that face. Oh, wait. What? There's a penis in the snails, right?

Wait. So it turns out that penis in the face. Oh, my goodness. Is actually like maybe one of the least strange things about snails. Soren, you look at snails.

And you think like anything. I haven't ever thought. Fine. You don't even think about snails. And I'm here to tell you that there is so much to see when you look at a snail, including a sex life that I don't think any of us saw coming.

“And so that's what we're going to do today.”

We're going to do snails. Are they going to do each other? And we're just going to watch. And I'm in. Okay.

And told here. Our guy, Menno, is going to be our guide. Exactly. So let's go. Okay. Well, to begin with, I wasn't originally interested in snails.

I mean, as a school boy, I was mostly interested in insects and birds. But you can study things in snails that you cannot study in insects. And that often has to do with the fact that they move so slowly. So you can see. You can catch them.

You can catch them. You can mark them. So I've put numbers on snail shells and found them back a year later or sometimes two years later, sitting on the same tree that they were sitting on when I marked them. No way.

That's cute. You know, people do that with insects too. But the chance of finding them back is much smaller than with snails who mostly sit where you left them. So they call this the rate of dispersal.

So that's basically the average distance between where an animal is born and the place where

it has its first reproduction. OK. And in snails that's usually between one and five meters. Oh, really? So that's not very far at all.

It's not very far at all. And that's the consequence of that is that you. And that's really what God would got me hooked on snails is that you can see evolutionary patterns on a human scale, which normally you would need entire continents for. So in, in create where I did my PhD, I would, I would walk through the mountains and with every

step, I would see subtle changes in the way the snail shells look. So if you cover a few kilometers, you can see snail shells around you sitting on the rocks changing from smooth to ribbed and from large to small. So you basically can walk through evolution. So when he's taking this walk, there's like a giant cliff of rock.

And in one tiny patch, there are species of tiny snail.

And then they settle there and evolution acts on them.

“And then some of them leave and go to another nearby patch of rock.”

And so basically you can walk patch to patch to patch and see how evolution is shaped these snails. Well, I'm fascinated by the idea that you can walk along this. But I'm like, yeah, what do you see when you go a slightly different shell or different antenna? Well, I'm not slimeier or less slimeier. Oh, you're looking at both the size.

Whether it's a flat shell or a tall, spireshaped shell, whether it has any and your ribs. But sometimes the shells between different species are very similar. They're just smooth and spiral leans. You can't really tell one species from the other very easily.

And you have to start to dissect. And with slugs, of course, you don't even have a shell.

So there you always have to dissect and which snails and slugs are as closely related as they look.

Yeah, slugs have evolved from snails. But during that process, they've lost their shell. Actually, many slugs don't haven't completely lost their shell.

“So usually you need to dissect them to really be sure what you're dealing with.”

And then you start meeting all this complex, this whole complex, genital world of snails straight to the genitals. Yes. I should have known, given that you. I was like snails have genitals.

Yeah, when you have species that are very closely related and very similar on the outside, usually they're reproductive organs, their genitals are wildly different. So genitalia are the organs that evolve the fastest among all organs in an animal's body. And the result is that anything that's is possible in evolution is going on in genitalia is really where the rubber hits the road. So just to set the scene here, the snails that menoe is talking about are hermaphrodites,

which means that they are both male and female at the same time. So they have both male and female parts inside their little slimy snail body. So snails are very asymmetric in the way their bodies are shaped. And the result of that is that snails usually have their genital opening on their right hand cheek. So you have these eye tentacles and a little bit behind the right eye tentacle.

“There's a little opening, very hard to see.”

And that's the place where both the penis and the vagina sit. I like it, it's on their right hand cheek, not even the butt cheek, just on the face. On their chest, yeah. So when they make, they have to bring these openings together. So usually they make face to face or actually cheek to cheek.

Dancing cheek to cheek. Exactly. Then they have to get these two openings together. And then both of these animals inferred their penises, which are inside their bodies.

But they basically inferred like a finger over glove.

So like the like if you have a glove or something and you pull your hand out and the finger goes inside the glove. That's how it is tucked in. And then when the snail gets to another snail and wants to meet with it, puffs that finger back out again. Yeah, well that's that's then true for the for the penis, the vagina stays where it is. And the penis of the of the one partner pushes in to the vagina of the other partner.

And simultaneously, feisty versa. So when you see the mating, you see basically two fingers connecting them through that little opening. Okay. That's the first step. But it does take several hours usually. Wow.

Yeah. Today many snails mate for, you know, two, three, four, five, up to seven hours. I've seen snails mating for the entire night. They usually mate during the night. So it can take the whole night for them to get all this gross.

This, this process underway. It reminds me of some sort of like dial up internet. Yeah. Exactly. He'll like, okay, we're connected.

Now we're waiting to connect. Almost as long as setting up this interview took. Yeah. Yeah. So.

Oh, my gosh. And they are just connected by these, these fingers the whole time. Yes. It, again, it depends on the species. This is really where the evolution of genitalia kicks in.

There are these fingers. There are also sort of tongue-like structures. There's one family of slugs that has these, which with which they lick each other. And these tongues are attached to the penis. There are also species that don't insert their, their penis is into the partner.

But they keep the penis is dangling on the outside and the sperm is transferred by sort of handshake from one penis tip to the other penis tip. There's a species of tiger slug from from southern Europe where this happens at the end of a penis

So that would be like 25 inches more even I think.

That's two feet. No more. 35 inches. Yeah. Yeah.

It's, it's three feet. It's about three feet.

“And these are actually contenders for the longest penis is compared to body lengths in the animal world.”

Well, yeah. It seems like it would just tip over a slug. Yeah. Like spaghetti. I mean, like cooked spaghetti is very flexible.

Yeah.

So they hang from a, from a tree in these penis is dangled down and they entwine.

And at the tip of the penis, the, the sperm package is transferred. Oh. So the sperm package is quite large. It's quite nutritious and it has millions of sperm in it's sperm cells. Okay.

And it's, it's not, they don't produce it beforehand. They produce it while they're mating. So they have to wait for that sperm package to be ready and filled with sperm. And that travels then through the penis into the sperm receiving organ of the partner. And again, this happens in both directions simultaneously.

“But it's only like one, one out of a thousand sperm gets to go to where the eggs are.”

The rest is being digested is being eaten. Oh, they can eat the sperm. Yes.

They can actually just kind of absorb it and like use it to live off of.

Use it as a food source. They could do that or they can like store. They have a, a, a way to store sperm. They're just not, now it's not the right time for me to, I'm just working on my snail career. And I don't want to get pregnant.

I've been coming down there. Yeah. It's funny, but like if you are a snail who spent the better part of seven hours. Getting ready to swap sperm. You don't want it to be eaten, you know.

And so to prevent that from happening. The sex game becomes less of a partnership dance. And more of a duel. A duel. Which involves all these weird organs that they use in their reproduction.

Like sperm storage organs and sperm digesting organs and. And then darts, glands and darts sex and it's a, it's a whole circus of sexual extravagance. That is coming up after the break. Okay. Hey, Lulu here and this episode is sponsored by Better Help.

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I'm Molly. You're soaring. Yes.

“And I think we are about to have a duel.”

I promise to duel and duel you shall get, which is like there are two snails. They are about to swap sperm, but they want to better their odds for that sperm to become babies. And so at this moment, they bring out their love darts. Love darts. Love darts.

They are produced in an organ called Colta Dartsek. And the darts is a little limestone needle made from the same material as the shell. Shaped like a little dagger. Oh. Really?

Yeah.

Can I share my screen with you?

Sure. Screen shot. Okay. Ready? Whoa.

It looks like whittled bone. Like white bones. It's almost like a tool.

“Like, like you'd imagine, like you'd find in like an archaeological site.”

Was it early needles that early humans used? Yes. You know, like, they'd be like early humans crafted this thing. Crafted a needle out of bone. Yeah.

Yeah. Oh, yeah. It's beautiful.

But the one on the far the top right one, the jet looks like an arrow.

Well, there are species in which the dart looks surprisingly like an arrow. You've drawn when you work it. Even like a little feathery thing that's in the back of the air. There's a little like, yeah. What are they called?

Those are like fletchings, fletchings. In other species, it's more like a flat knife shape. And I've studied the species in Borneo, which is more like a like a hypodermic needle. With holes along the side. So they're about a centimeter long.

One centimeter. Yeah. So yeah, that's almost half an inch.

“They are present in a snail even if they're not mating.”

And they can feel them crushing when you're eating a snail. So you'll be like eating snails. And then you'll go, oh, just hit a love dart. Well, I would most people wouldn't. They would just--

No, yeah, you. I'm talking to you. You're specifically, no? Yeah, yes. Yes, I would.

My gosh, I've never actually had snails.

But now I-- Okay. Well, I don't know how if I would feel if I was eating the love dart. Maybe bad? Yeah.

No, you ate that entire reproductive system as well, including the love dart. But the sort of dart is not a penis. It's not like delivering sperm. The dart is not a penis. Okay.

The dart plays a specific role.

“So what they do with the love dart is they expel this dart with considerable”

force into the partner. Like they shoot it. They shoot it. Yeah, yeah. Some species shoot it.

Some species push it. But like the Oscar go that we eat. It really shoots it with force. And it goes fast. So there's a muscular organ that's very fast and forcefully pushes it into the skin of the partner.

And in some species, it is withdrawn after that. And in other species, it's sort of a disposable dart and it stays in the-- Yeah. And where are you shooting the dart toward? Like what do you want to hit?

It looks like you mostly want to hit the skin very close to that genital opening. But sometimes-- So they hit the face. The other cheek. Okay.

And what is it doing with the dart? Is it shooting a material? Substance is just like, "Hey, I want your attention." Well, that was a mystery until quite recently. People thought, yeah, it was some sort of stimulation.

You know, just like when you see lions mating, they're also biting into each other's head. And sharks also do that. So why not shoot a dart? It could be something like that.

And then people thought maybe it's maybe it's what they call an up chill gift. So a donation of calcium to help the partner build the eggs for the offspring that they're going to produce. Because eggs use calcium. Because the eggs need calcium for the shells. But then research in the 1990s showed that there was barely enough calcium in a dart to produce the shell for one egg.

So that also wasn't the answer. But research by Ronald Chase and Yoraskuna showed that there were actually hormones being delivered into the body of the snail that is being shown. Yeah, yeah, yeah. So the dart gland produces this mucus that has inside of it a essentially a sex hormone. And the the arrow is either covered in or full of the sticky goo.

These hormone-like substances get into the bloodstream of the animal that receives the dart. And it turns out that those hormones, they produce involuntary spasms in the female organs of the animal. The organs of the partner which increases the uptake of sperm. Oh, okay. So it's a kind of manipulation.

You're saying that when this hormone hits the the system of the partner, what you could call the vagina. And it like makes it seize or like cramp or something. It's a little bit more complicated than that, unfortunately. So it's actually that behind the vagina there are these two pockets. One is a storage room.

The other is a digestion room. And when the hormone hits and causes these like tiny spasms. Sounds almost like like a little orgasm. Yeah, but it causes muscles to contract. And what the hormone does is it sort of creates or it causes the entrance of that digesting organ to close off.

And all of that can lead to the sperm, you know, being kind of pushed toward an egg.

“So if you shoot your dart right, you probably will gain more offspring than if your if your dart misses its target.”

There's also species in Japan, which don't shoot a love dart, but they step multiple times. And every time they step, the dart is recharged with new hormone. So they have this this sort of dip it in the glands in their body. And then they push it in again and then they pull it out and dip it in again and push it in again. So there's a snail where this has been seen the sort of the snail would be seen.

Stabbing its partner. 3,300 times in rapid succession. So probably it's there. It's also a matter of more is better. They just keep pumping this hormone into the partner and vice versa.

And the partner lived through 3,000 steps.

Yeah, yeah, it's just a single it's going into the same wound all the time. So it's not making you wounds, not like Caesar. But she says not like Caesar. Yes. So yeah, there's pictures of these snails that are mating and there's this this dart is sticking through the head of one of the snails.

It's that sort of the the fledgings are still coming out on one side of the tip is coming out on the other side. So they're like visible to the naked eye. Yeah, I find them in my garden after a wet night. They they when snails have been mating. Sometimes they yeah, they they leave those those darts on the on the floor.

“Wait, do you think I've seen a snail dart and just not known it?”

Could be. And it doesn't kill it. It doesn't kill it. No, they don't seem to suffer too much from it. Of course, they don't have a brain like we do that can be hit.

So they just have some ganglia which are in a different place. So it may be nothing. Maybe the ganglia are in a different place because they're like we've seen these darts. We're going to move on over to the stomach. I wouldn't be surprised, yeah.

And I'm just thinking about you and your back yard just like picking up love darts. You're like, wow, that's nice. It was a big night. Yeah, exactly.

“It's usually in the spring when it's warm and but rainy.”

When we have a spring like that that you you see snails mating. And you you often find you find these slime spots which are sort of a tell tell sign that they've been having fun. And you find these love darts lying on the floor because they do sometimes missed. And sometimes they also expelled them from their body after mating. How would they get it out?

Like if I have a love dart through my head. Yeah, how am I extracting it? Maybe if it's completely through, you wouldn't be able to get it out. But if it's sort of sticking in the skin then yeah, I guess just by by movements. It's wiggles out like just like a like a splinter in your skin.

And you as a scientist, I'm assuming that love darts are interesting to you. And that and that finding out how they worked is of interest to you. So like I'm just curious as to like what insights it gives you. Well, what insights it gives me is that it's so abundantly clear that the evolution of reproductive organs. It's a complete madhouse of evolutionary novelties and measures and countermeasures.

And warfare sometimes but also persuasion. Let's say on the male side an evolutionary change that allows the male to bypass any control of the female. This will then immediately be followed by an evolutionary countermeasure on the female side that regains control for the females. And that this all these changes accumulates on top of each other. And it's very unpredictable in which direction it will go.

And the fact that these darts have evolved multiple times, they look different in different species that some species have one. Some species have two, some species have four. Some species have this disposable darts, some reuse them. Some stab ones, some stab thousands of times.

Some don't form darts on their first mating, but only on their second and later.

So even within the darts that's so much variety that it really drives home the fact that this genital evolution. You can see anything in evolution sort of encapsulated in what goes on in these genitals. I mean, I evolution aside in just sort of guy had no. Like I thought snails maybe they just slime up next to each other and then there's a sack of eggs or something like guy had no. Yeah, it's like you just look at these things and you think slime ball.

Yeah. You don't think theater of evolution.

Look at what I'd been missing this whole time.

“I think of one of the things I most fascinated by is that I can see it that like I could go pick up a little love dart.”

It's almost like it's almost like being so funny to say this to a scientist. And I do really believe in science, but it's like it's almost like being like oh my god, fairies do exist. Like it's like being exposed to this world that just feels so other and tiny and magical, but like there's a little remnant of it left behind. Yeah. And I know that it's real because of that.

Yeah, and of course there's also these medieval marginalia. I don't know if you've heard about these. No, what's that? The marginalia are these little embellishments on in the margins of medieval books where you know there would be little scenes of a hair or duck or fox chasing a bird.

But there's also lots of marginalia about nights fighting with snails with swords.

Really? And yeah. And people have also thought maybe that has to do with the love darts. There's a whole literature on this. And so it feels like there was almost like a time of the world when we were bumping into love darts more.

Hmm. Yeah. Okay. Oh yeah, this pet story is busy. Okay.

That's that maybe. Do you think that some scientists or some naturalist or just some person walking along millennia go? Found a love dart on the ground and then made up the myth of Cupid? Yeah.

“There is actually some people think that's how the myth of Cupid evil.”

Wow. Stepping over our exploded bag of trash. Wait, so. Could I go find a love dart? There, there in prospect park in Brooklyn on trees.

So there are some local love darts. Definitely. You'd have to wait for them to come out of hibernation, which would be in late April probably. Okay. And then they usually start mating quite soon thereafter.

So if you go out early in the morning and look. Yeah, on on walls on trees on tree trunks. And as soon as you see two snail shells that are sitting really close together, touching each other, then they're usually mating. Then you can look from the side and yeah, then you might see a dart sticking out or maybe a dart is lying or being stuck on the slime that they're sitting on. You'd give it us a new thing to go into the world in five because the ground's not thought yet.

You're right. I mean, the story like this could make people go out and think I want to see my love darts for myself. And I'm going to go into the park and find snails that are mating. The wet tree. And they will. Not quite yet, but soon.

It's a miniature world that exists. This would be where you could find a snail or two. That would be wonderful. [Music] This episode was produced by Monumet Galker, Anna McEwen and Molly Webster.

It was edited by Alex Nesin, FactCheck by Diane Kelly, and reported by yours truly.

“If you want to read more about snail sex, you should go check out Menos book called”

Nature's Nether regions. There's a whole chapter on snail sex. Menos still tells in is a evolutionary biologist at Leiden University in the Netherlands. Thank you, Menos. I also want to give a shout out to Erin Chase.

I first heard about love darts from Erin very recently.

And in fact, it is his dad, Ronald Chase, who discovered what the love darts were actually doing to snail. If you want to read more about how I found out about love darts, check out our newsletter or go sign up for the newsletter, which is at radiolab.org/newsletter. For those of you who are lab members, we are dropping some snail extra content on the lab.

If you are not lab members, go sign up now and you can learn all about snugg life. And finally, you best believe that the second it thaws outside. I will be out there looking for love darts and I'd love for you to join me. So keep an eye on social media and we'll keep you posted.

Spring is a coming. This is Radio Lab. Thanks for listening. Hi, I'm Gabby.

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