Snail Sex Tape

Hey, it's Molly Webster. I have a surprise for you. Next month, myself and producer Mona Medgalker are going to do an AMA about our snail sex tape episode. You can ask us anything about snails and the behind the scenes of making an episode work. How long did it take us to make? How did we come up with the sound effects? Why are snails and slugs related? The AMA will be on April 16th and in order to come you have to be a member of the lab. So go to radiolab.org slash join right now.

Sign up, use the code word SNAIL to get a discount on your membership. And also if you sign up now, you get a SNAIL enamel pin. If you're already a member of the lab, come to the AMA. Thank you for listening. Can't wait to see you there April 16th. Oh wait, you're listening.

Or listening to Radio Labs. Am I recording? I'm recording. Does your mic have fancy green lights on it? Does yours not? No. It like tells me how loud it is. And it also I can also mute it dire can you hear me? You can't hear me anymore. No, I can't still. Oh, you can? Yeah. Wait, what does that button mean then?

Button, button. I'm Molly Webster. This is Radio Labs. Button, button. Um, okay. And today I am joined by our executive editor Sorn Wheeler. What are we doing? Why are you here? Well, you're here because I'm gonna take you on a walk. Oh, uh you're gonna take me on a walk? Where? In a lowland area along the Kinabatangan River. We're gonna follow this guy, Meno. He's an evolutionary biologist. Seems like a nice guy to go on a walk with.

Menno's going to take us deep into Borneo. It's tropical humid limestone forest, so it's it's really wet. There's lichens, there's ferns, or caves. and vines and climbers. And he is looking for something. Okay. And actually I also went on a walk to look for this something. Whew. My walk. was not in Borneo, it was in Brooklyn in February. So less orchid, dog poop, more cigarettes, trash.

Here's a pigeon. So this is something that you can find in both Borneo and Brooklyn. Yes. Um 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. Whoo and then right there there is a glass tank. Like pressing my face up against the glass. Really put my face to the surface of the rock and then Oh my goodness. I see these miniature tiny, tiny snails.

Snails. Mm-hmm. It's got a little brown shell with whirls. Is the thing that we went on a walk to see. Right. It's got two little antennas. And I just can't imagine a penis coming out of that face. Oh, wait, what? That uh the there's a penis in the snail's face. So it turns out that penis in the face is actually like maybe one of the least strange things about snails.

Soren, you look at snails and you think I don't think anything. I haven't ever thought about it. Okay, 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 um a sex. Life that I don't think any of us saw coming. And so that's what that's what we're gonna do today. We're gonna do snails, or they're gonna do each other, and we're just gonna watch.

In. I'm in. Okay. And our guy Menno is gonna be our guide. Exactly. So let's go. Okay. Um Well, to begin with I wasn't originally interested in snails. I mean as a schoolboy I was I was m 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 They move so slowly, so you can see You can catch'em. You can catch them, you can you can mark them. So I've I've 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. much smaller than with snails who mostly sit where you left them. So so they they call this the 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. Okay. And in snails that's usually between one and five meters.

Oh really? That's not that's not very far at all. It's not very far at all. And that's the the consequence of that is that you and that's really what got what 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 Crete where I did my PhD, I would I would walk through the through the mountains and with every step I would see

subtle changes in the way the snail shells looked. 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 kind of walk through evolution. So when he's taking this walk, there's like a giant cliff of rock, and in one tiny path. there are a species of tiny snail, and m one day some of those individuals wander over to a very nearby patch of rock.

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 has shaped these snails.

Well I'm fascinated by the idea that you can walk along this but I'm like, Yeah, what do what do you see when you go? A slightly different shell or a different antenna or I It's slimier or less slimier or Oh you're you're looking at the well the size, whether it's a flat shell or a tall, spire shaped shell. uh whether it has any any ribs. But w sometimes the shells between different species are very similar. They're just smooth and spiral y and

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 the bigger. Wait, so 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 uh 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.

Um and then you start meeting all this this complex uh this this whole complex genital world of of snails Straight to the genitals? Yes. I should have known given that you should 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 they're reproductive organs, they're genitals. are wildly different. So genitalia are the organs that evolve the fastest

among all organs in an animal's body. Um and the result is that anything that's is possible in evolution is going on in genitalia. That's really where the Where the rubber hits the road. So just to set the scene here, the snails that Menno is talking about are hermaphrodites. Okay. 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.

Um 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 tet tentacle there's a little opening, very hard to see. I like it, it's on their right hand cheek, not even their butt cheek, just on their face. On their just yeah. Yeah. So usually Yeah. Um they have to get these two openings together. of these animals avert their penises? Which are you?

inside their bodies and but they they basically Like the finger of a 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. is tucked in and then when the snail gets to another snail it wants to mate 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. Uh and the the penis of the of the one partner

pushes into the vagina of the other partner and simultaneously vice versa. So when you see them 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. Really hours? Yeah, yeah. An entire night. They usually made during the night, so it can take the whole night um for them to get all this this process underway. It reminds me of some sort of like dial up internet. Yeah. Exactly.

You're like, okay, we're connected, now we're waiting to connect. Uh almost as long as setting up this interview took. Yeah. Um yeah. So um Oh my gosh. And they are just connected by this these fingers the whole time. It it again it depends on the species. This is really where the um evolution of genitalia kicks in. There are these fingers. There are also species that don't in Yeah. By a 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 that is almost a meter long. Like twenty-five inches, more even I think. That's two feet. No more. Five inches. Yeah. Yeah. It's it's three feet. It's about three feet. And these uh so these are actually contenders for the longest penises compared to body length in the animal world. Um well yeah, it seems like it would just tip over a slug. Yeah, well they're it's like spaghetti.

A tree and these penises dangle down and they entwine, and at the tip of the penis, the sperm package is transferred. So the sperm package is quite large and quite nutritious and it has millions of sperm in it. Sperm cells. Um and it is 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 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.

Um they could do that or they can like store they have a s a a a way to store sperm so if they're just not now is not the right time for me to I'm j working on my snail career and I don't want to get pregnant. The up and coming actor. Um 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 l wanna to be eaten, you know? And so to prevent that from happening, the sex game becomes less of a a partnership dance. Which involves it?

Uh Digesting organs.

Darts. Did you ever wonder what it's like to live line? Hidden in the woods, not speaking to a single soul. Or wander the desert, uncover a hidden well, and Deepest water hole. For two thousand miles. Takes you there with amazing stories told by the people who live them with an original soundscape that drops you directly into their shoes.

I'm Molly. You're Soren. Yes. And I think we are about to have a d duel. I promised a duel and a duel you shall get, which is like there are two snails. They are about to swap. But they want to better their odds for that sperm to become babies. And so at this moment, they bring out They're love darts. Love darts? They're produced in an organ called called the Dart. And the dart is Um shaped like a little dagger. Oh. Um Really? Yeah. Can I Google it? Can I share my screen with you?

Sure. Screenshot. Okay, ready? Whoa. It looks like whittled bone, like white bone. It's almost like a tool. Like like you'd imagine like you'd find in like an archaeological site was early needles that early humans use. Yeah. Yeah, oh yeah. But the one on the far the top right one legit looks like an arrow. Well there are species in which the dart looks Uh surprisingly like an arrow you've drawn.

Mm when you were a kid. Even like the little feathery thing that's in the back of the air, there's a little like Yeah. What do they call it? Those are like fletchings. Fletchings. In other species it's uh more like a flat knife. shape. Um and I've studied a species in Borneo, which is more like a like a hypodermic needle with holes along the sides. So they're about a centimeter long. One centimeter. Yeah. So uh yeah that's almost half an inch.

They are uh present in a snail even if they're not mating. So and they you can feel them crushing when you're eating a 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... Talking about you specifically, Meno. Yeah, yeah, yes. Yeah. 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 eat that entire reproductive system as well, including the love dart. But the 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 escargot that we eat, it really shoots it with with force and it goes fast. Uh so there's a 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 in the board. And where are you shooting the dart toward? Like what do you want to hit? It looks like you mostly want to hit the the skin very close to that genital opening. But sometimes So the head, the face.

And what is it doing with the dart? Is it is it is it shooting the material, substances just like, hey, I want your attention Well that was a mystery until quite recently. Uh people thought yeah, it was some sort of stimulation. Uh you know, just like you when you see lions mating, they're also biting into each other's heads, and and sharks also do that, so why not shoot a dart? It could be something like that.

Uh and then people thought maybe it's uh maybe it's what they call a nuptial gift, so a donation of calcium to help the partner uh build the eggs. for for the offspring that they're going to produce? Because eggs use calcium? Because the eggs need calcium for the shells, but um Okay.

Then research in the nineteen nineties showed that there was barely enough calcium in a dart to produce the shell for one egg. So that also wasn't the answer. Uh but research by Ronald Chase and uh Joris Kuna showed that uh there were actually hormones being delivered. Yeah. Yeah. Yeah. So the dark 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 this 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 partner, which increases the uptake of sperm. Whoa. Okay. So it's a kind of manipulation. You're saying that when this hormone hits the s 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. Um it's um So it's actually that behind 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 a like a little orgasm or something. Yeah. But it causes muscles to contract.

And what the what the hormone does is it sort of Create uh or it causes the entrance of that digesting organ to to close off. And it also kind of pushes sperm out of the storage chamber. 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

should a love dart but they stab multiple times. Oh it's just a shit. And and every time they stab the the dart is recharged with new hormone. So they have this they sort of dip it in the gland, in their body and then they push it in again and then they pull it out and dip it again and push it in again. So there's a snail where this has been seen the so the the snail would be seen stabbing its partner three thousand three hundred times in rapid succession.

Uh so probably it's there it's also a matter of more is better. So They they just keep pumping this hormone into the partner. And vice versa. And the partner lived through three thousand stabs. Yeah, yeah, yeah. It's just a single it's going into the same wound all the time, so it's not making new wounds, not like Caesar.

But uh did you say it's not like Caesar? Yes. Um Uh so yeah there's pictures of a of these snails that are mating and there's this this dart is sticking through the head of one of the snails at The the so the the fletchings are still coming out on one side and 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. Uh they they they when snails have been mating and 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. Uh And it doesn't kill it? It doesn't kill it. No, they don't seem to s suffer too much from it.

Um 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 Maybe nothing vital is the same. Picking up love darts. You're like, Wow, last night 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 f you've you f you see you see snails mating, um and you s you f often find you find these slime spots which are sort of a telltale sign that they've been having fun. And you find these uh love darts lying on the floor because they do sometimes miss and sometimes they also expel them from their body after mating. How would they get it out? Like if I have a love dart through my head 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.

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 um of evolutionary novelties and s measures and countermeasures and warfare sometimes, but also persuasion.

Um 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 uh accumulate 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 uh have disposable darts, some reuse them. Um some stab once, some stab m 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, I'm just sort of I 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 I had no

Yeah, it's like it's like you just look at these things and you think slime ball. Yeah. You don't think theater of evolution. No. Or three foot penis or look at what I'd been missing this whole time. I I think one of the things I'm 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 e it is 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 it's like being exposed to this world 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 these

Medieval marginalia. I don't know if you've heard about these. No, what's that? So marginalia are these little embellishments on in the in the margins of medieval books. Okay. where, you know, there would be little scenes of a hare or a duck or a or a fox chasing a bird. But there's also lots of marginalia about knights fighting with snails with swords Uh really? And yeah. And people have also thought maybe that has to do with the love dart.

There's a whole literature on this uh it's it's so it feels like there was almost like a time of the world when we were bumping into love darts more. Oh my god, this pet story is busy. That's that's that's it. Do you think that some scientist or some naturalist or just some person walking along millennia ago found A love dart on the ground and then made up the myth of Cupid? Yeah, there is actually some people think that's that's how the myth of Cupid even Wow.

Stepping over an exploded bag of trash. Um wait so Could I go find a love dart? Uh well they're they're in Prospect Park uh in in Brooklyn. Oh uh on trees. Um 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 um yeah, on on walls, on trees, on And as soon as you see two snail shells that are sitting really close together, touching each other, then they're usually mating.

And yeah, then you might see a dart sticking out or maybe a a dart just lying or being s stuck on the slime that they're sitting on. You've given us a new thing to go into the world and find. The crown's not thought yet. You you're right. I mean this the story like this could could make people go out and think I I want to see my love darts for myself.

I'm going to go into the park and find snails that are mating. And they will. Not quite yet, but soon. It's uh it's a miniature world that exists. This would be Where you could find a snail or two.

Booper burp. This episode was produced by Mona Madgauker, Annie McEwen and Molly Webster. It was edited by Alex Neeson, fact-checked by Diane Kelly, and reported by yours truly. If you want to read more about snail sex, you should go check out Mennow's book called Nature's Nether Regions. There's a whole chapter on snail sex.

Menno Stiltaussen is an evolutionary biologist at Leiden University in the Netherlands. Thank you, Menno. And I also want to give a shout out to Aaron Chase. I first heard about love darts from Aaron very recently, and in fact, it is his dad, Ronald Chase. Who discovered what the love darts were actually doing to snails? 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 Radio Lab даторgс 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 SNUGLIFE. 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. For now I am Molly Webster. Spring is a coming. This is Radio Lab. Thanks for listening. Hi, I'm Gabby.

Here are the staff credits. Radio Lab is hosted. By Lula Miller and Letif Nasser. Soran Wheeler is our executive editor. Sarah Sandbach is our executive director. Our managing editor is Pat Walters. Dylan Keefe is our Director of Sound Design. Our staff includes Jeremy Bloom, W. Harry Fortuna, David Gable, Maria Paz Gutierrez, Sindhu Ninasambandan, Matt Kealty, Mona McGaughger, Annie McEwen, Alex Neeson,

Sarah Kari, Rebecca Rand, Anisa Vizza, Arian Wack, Molly Webster, and Jessica Young. With help from Gabby Santos. Our fact checkers are Diane Kelly, Emily Krieger, Natalie Middleton, Angela Mercado, and Sophia. Leadership support for Radiolab Science Programming is provided by the Simons Foundation and the John Templeton Foundation. Foundational support for Radiolab was provided by the Alfred P. Sloan Foundation.

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