Snail Sex Tape

Summary

Radiolab: "Snail Sex Tape" (March 6, 2026)
A Detailed Episode Summary

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Episode Overview

In the “Snail Sex Tape” episode, Radiolab ventures into the peculiar, surprising, and often overlooked world of snail reproduction. Guided by evolutionary biologist Menno Schilthuizen, host Molly Webster—and, for comedic effect, executive editor Soren Wheeler—explore the evolutionary oddities and jaw-dropping intricacies of how snails find mates, exchange sperm, and duel for reproductive dominance. From snails’ hermaphroditic anatomy to their use of weaponized “love darts,” this episode turns slimy backyard creatures into the stars of a miniature Game of Thrones, where genitals, strategy, and evolutionary arms races play out in slow motion on leaf litter and tree bark. The tone oscillates between curiosity, humor, and awe, infusing science with a sense of magic hiding in plain sight.

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Key Discussion Points & Insights

1. The Allure of Snails and Studying Evolution Up Close

• Accessible Evolution: Menno describes being drawn to snails because their slow movement and limited dispersal (just 1–5 meters from birthplace to reproduction site) allow scientists to observe micro-evolution "on a human scale." (05:04)
• Visual Variation: Evolution in snail populations is so gradual and local that, “with every step, I would see subtle changes in the way the snail shells looked” (05:22).
  • QUOTE: “You basically can walk through evolution.”
    — Menno Schilthuizen, (05:46)

2. Inside the Snail: Anatomy and Genital Madness

• Hermaphrodite Wonders: Most snails are hermaphrodites—with both male and female organs—packed inside their asymmetric bodies.
  • Their genital opening is usually behind the right eyestalk, described as being “on their right hand cheek” (08:13), leading to face-to-face (cheek-to-cheek!) mating rituals.
  • QUOTE: “So when they mate, they have to bring these openings together. So usually they mate face to face or actually cheek to cheek.”
    — Menno Schilthuizen, (08:38)
• Wild Genital Evolution: Even in nearly identical species, reproductive organs are “wildly different.” Genitalia evolve the fastest among bodily organs because they are at the front line of evolutionary competition (07:27).
  • QUOTE: “It’s really where the rubber hits the road.”
    — Menno Schilthuizen, (07:52)

3. Snail Sex in Slow Motion: Process & Strategies

• Courtship & Copulation: Snail mating can last from 2 to 7 hours, often happening overnight. Mating involves everted penises (like a glove turned inside out) that connect “fingers through that little opening” (09:06).

  • Memorable Comparison: “It reminds me of some sort of like dial up Internet.”
    — Molly Webster, (10:03)

• Genital Variety: Some species don't insert penises but exchange sperm via a "handshake"; others (like the tiger slug) have penises up to 3 feet long, almost preposterous compared to their body size (10:30–11:20).

  • QUOTE: “There’s a species of tiger slug from southern Europe ... where this happens at the end of a penis that is almost a meter long.”
    — Menno Schilthuizen, (11:00)

• Sperm as Food and Storage: Snails can digest sperm as a food source or store it for later use, sometimes prioritizing career over child-rearing, as Soren jokes (12:16, 12:29).

  • Memorable Moment:
    Soren (joking): “It’s not the right time for me to... I’m working on my snail career and I don’t really want to get pregnant.” (12:29)

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4. The Love Dart Duel: Evolutionary Arms Race

• Love Darts Introduced: To ensure their sperm gets used, snails deploy a calcium “love dart”—a needle or arrow made from the same material as their shell—kept in a specialized organ (dart sac) (17:04).

  • They’re actual projectiles, sometimes shot, sometimes stabbed, with surprising velocity and precision.
  • QUOTE: “So what they do with the love dart is they expel this dart with considerable force into the partner.”
    — Menno Schilthuizen, (19:06)
  • Visual Description: “It looks like whittled bone, like, white bone.”
    — Molly Webster, (17:26)

• Dart Anatomy & Variation: Darts can resemble arrows, knives, or hypodermic needles, with some species having multiple darts, up to four at once, varying by evolutionary lineage (18:03–18:17).

• Not Delivering Sperm: The dart isn’t a penis. Instead, it delivers a payload of hormones that manipulate the mate’s reproductive system, increasing the odds the shooter’s sperm fertilizes eggs (19:02–21:18).

5. Hormonal Sabotage and Stabby Tactics

• Hormone Effects: The dart’s mucus contains hormones inducing muscle contractions, which close off sperm-digesting organs and favor sperm storage organs—giving the dart-shooter’s sperm a fertilization advantage (21:18–22:26).
• Technique & Persistence: In Japanese species, some snails stab over 3,000 times, pumping more hormone with each jab. Occasionally, a dart will be visibly sticking through a snail’s head but causes little harm (23:26–24:26).
  • QUOTE: “You see snails mating, and you find these slime spots which are sort of a telltale sign that they’ve been having fun. And you find these love darts lying on the floor.”
    — Menno Schilthuizen, (24:41)

6. Evolution in Action: Measure, Countermeasure, and Ongoing Arms Race

• Escalation and Diversity: Darts have evolved multiple times, in different forms (disposable, reusable, single/multiple). Each new male adaptation is countered by new female countermeasures, leading to “a complete madhouse of evolutionary novelties” (25:42, 27:07).
  • QUOTE: “All these changes accumulate on top of each other and it’s very unpredictable in which direction it will go.”
    — Menno Schilthuizen, (25:48)

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Notable Quotes & Memorable Moments

• On Intimacy and the Unexpected:
  “You just look at these things and you think slime ball. You don’t think theater of evolution.”
  — Molly Webster, (27:22)
• On Discovery:
  “It’s almost like being like, ‘oh my god, fairies do exist.’ 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.”
  — Molly Webster, (27:32)
• On Medieval Marginalia:
  Medieval manuscripts often depicted “knights fighting with snails.” There’s speculation that these love darts inspired the myth of Cupid or such medieval imagery (28:04–29:13).

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Timestamps for Key Segments

| Time | Segment/Topic | Highlights | |----------|------------------------------------------------|-----------------------------------| | 03:01 | First view of snails, snail anatomy | Start of snail focus | | 05:04 | Evolution in snail populations | Human-scale evolution | | 07:24 | Wildly diverse snail genitals | Fastest-evolving body part | | 08:13 | Hermaphroditism, anatomical details | Cheek-to-cheek mating | | 09:06 | Mating process: everted organs | Hours-long copulation | | 10:30 | Penises as long as three feet | Extreme snail adaptations | | 12:16 | Sperm ingestion/storage | Snails as sperm eaters/storers | | 17:04 | Introduction of love darts | Anatomical description | | 19:06 | Function and shooting of love darts | Hormonal payload explanation | | 21:18 | Hormonal manipulation, evolutionary arms race | Dart-induced muscle contractions | | 23:26 | Multiple stabbing, the arms race escalates | 3,300 times in Japanese species | | 25:42 | Evolutionary insight | Ongoing sexual “warfare” | | 27:32 | Awe and the magic of everyday nature | “Fairies do exist” moment | | 28:04 | Medieval marginalia & Cupid connection | Historical/literary echoes | | 29:31 | Where to find love darts in the wild | Prospect Park/Brooklyn tip |

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Episode Takeaways

• Snails are evolutionary hotbeds: Their reproductive strategies showcase sexual selection, arms races between partners, and extreme ingenuity in anatomy.
• Love darts are real and findable: They’re not myth—if you know where (and when) to look, you can find these remnants in your neighborhood.
• Science & wonder coexist: The episode blends humor, discovery, and detailed biology to reveal a hidden world of slime, sex, and strategy.

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For further reading, the episode recommends Menno Schilthuizen’s Nature’s Nether Regions—with a chapter on snail sex—and the Radiolab newsletter for “snug life” extras.

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“It’s a miniature world that exists.”
— Menno Schilthuizen, (30:38)

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End of Summary

Transcript

[Cotton Soren Wheeler]

Radiolab is brought to you by Progressive Insurance. Do you ever find yourself playing the budgeting game? Well, with the name your price tool from Progressive, you can find options that fit your budget and potentially lower your bills. Try [e-mail], progressive Casualty Insurance Company and affiliates. Price and coverage match, limited by state law. Not available in all states.

[Molly Webster]

WNYC Studios is supported by Odoo. When you buy business software from lots of vendors, the costs add up and it gets complicated and confusing. Odoo solves this. It's a single company that sells a suite of enterprise apps that handles everything from accounting to inventory to sales. Odoo is all connected on a single platform in a simple and affordable way. You can save money without missing out on the features you need. Check out Odoo at O D O O dot com. That's O D O O dot com.

[Cotton Soren Wheeler]

Oh, wait, you're listening.

[Menno Schildhausen]

Okay. All right.

[Molly Webster]

Okay.

[Menno Schildhausen]

All right.

[Cotton Soren Wheeler]

You're listening to Radio Lab Radio from wny.

[Molly Webster]

Am I recording? I'm recording.

[Cotton Soren Wheeler]

Does your mic have fancy green lights on it?

[Molly Webster]

Does yours not? No, it tells me how loud it is, and I can also mute it. Can you hear me? You can't hear me anymore?

[Cotton Soren Wheeler]

No, I can still.

[Molly Webster]

Oh, you can?

[Cotton Soren Wheeler]

Yeah.

[Molly Webster]

Wait, what does that button mean then?

[Cotton Soren Wheeler]

Button, button.

[Molly Webster]

I'm Molly Webster. This is Radiolab.

[Cotton Soren Wheeler]

Button, button.

[Molly Webster]

Okay. And today I am joined by our executive editor, Cotton Soren Wheeler.

[Cotton Soren Wheeler]

What are we doing?

[Molly Webster]

Why are you here? Well, you're here because I'm going to take you on a walk.

[Cotton Soren Wheeler]

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

[Menno Schildhausen]

In a lowland area along the Kinabatangan River.

[Molly Webster]

We're gonna follow this guy Menno.

[Menno Schildhausen]

Menno Schildhausen.

[Molly Webster]

He's an evolutionary biologist.

[Cotton Soren Wheeler]

Seems like a nice guy to go on a walk with.

[Molly Webster]

Menno's going to take us deep into Borneo.

[Menno Schildhausen]

It's tropical, humid limestone forest, so it's really wet. There's lichens, there's ferns, orchids and vines and climbers.

[Molly Webster]

And he is looking for something.

[Cotton Soren Wheeler]

Okay.

[Molly Webster]

And actually, I also went on a walk to look for the something. My walk was not in Borneo. It was in Brooklyn in February. So less orchid, dog poop, more cigarettes, trash. Here's a pigeon.

[Cotton Soren Wheeler]

So this is something that you can find in both Borneo and Brooklyn?

[Molly Webster]

Yes, in Borneo, it's down by the

[Menno Schildhausen]

riverbanks and the limestone cliffs in Brooklyn.

[Molly Webster]

Oh, no, I'm right here. You just make your way through one single door to a store. Whew. And then right there, there is a Glass tank, like, pressing my face up

[Menno Schildhausen]

against the glass really put my face to the surf surface of the rock and then glistening in the sun.

[Molly Webster]

Oh, my goodness.

[Menno Schildhausen]

I see these miniature, tiny, tiny snails.

[Cotton Soren Wheeler]

Snails.

[Molly Webster]

It's got a little brown shell with

[Cotton Soren Wheeler]

whorls, is the thing that we went on a walk to see.

[Menno Schildhausen]

Right.

[Molly Webster]

Got two little antennas, and I just can't imagine a penis coming out of that face.

[Cotton Soren Wheeler]

Oh, wait, What? That there's a penis in the snail's face.

[Molly Webster]

Wait, so it turns out that penis in the face.

[Cotton Soren Wheeler]

Oh, my God.

[Molly Webster]

Is actually, like, maybe one of the least strange things about snails.

[Menno Schildhausen]

What?

[Molly Webster]

Soren, you look at snails and you think.

[Cotton Soren Wheeler]

I don't think anything. I haven't ever thought of.

[Molly Webster]

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 a sex life that I don't think any of us saw coming. And so 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

[Cotton Soren Wheeler]

in. I'm in.

[Molly Webster]

Okay. And.

[Menno Schildhausen]

Oh, dear.

[Molly Webster]

Our Guy Menno is gonna be our guide.

[Menno Schildhausen]

Exactly.

[Molly Webster]

So let's go.

[Menno Schildhausen]

Okay. Well, to begin with, I wasn't originally interested in snails. I mean, as a schoolboy, I was 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.

[Molly Webster]

No way. That's cute.

[Menno Schildhausen]

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.

[Molly Webster]

Okay.

[Menno Schildhausen]

And in snails, that's usually between one and five meters.

[Molly Webster]

Oh, really? So that's not very far at all.

[Menno Schildhausen]

It's not very far at all. And that's the consequence of that, is that, you know, and that's really 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 Crete, where I did my PhD, I would walk 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 can walk through evolution.

[Molly Webster]

So when he's taking this walk, there's like a giant cliff of rock, and in one tiny patch, there are a species of tiny snail. And 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.

[Cotton Soren Wheeler]

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 a different antenna? Slimier or less slimier?

[Menno Schildhausen]

Oh, you're looking at the size, whether it's a flat shell or a tall spire shaped shell, whether it has any ribs. But sometimes the shells between different species are very similar. They're just smooth and spirally, 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.

[Molly Webster]

Wait, so snails and slugs are as closely related as they look?

[Menno Schildhausen]

Yeah, slugs have evolved from snails, but during that process, they've lost their shell. Actually, many slugs 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.

[Cotton Soren Wheeler]

Straight to the genitals.

[Molly Webster]

Yes.

[Cotton Soren Wheeler]

I should have known, given that you were.

[Molly Webster]

I was like, snails have genitals?

[Menno Schildhausen]

Yeah. When you have species that are very closely related and very similar on the outside, usually their 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 is possible in evolution is going on in genitalia. It's really where the rubber hits the road.

[Molly Webster]

So just to set the scene here, the snails that Menno 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.

[Menno Schildhausen]

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.

[Molly Webster]

It's on their right hand cheek. Not even their butt cheek, just on their face on their.

[Menno Schildhausen]

Just. Yeah. So when they mate, they have to bring these openings together. So usually they mate face to face or actually cheek to cheek.

[Molly Webster]

Dancing cheek to cheek.

[Menno Schildhausen]

Exactly. Then they have to get these two openings together. And then both of these animals evert their penises which are inside their bodies, but they basically evert like a finger of a glove.

[Molly Webster]

So 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 it wants to mate with, it puffs that finger back out again.

[Menno Schildhausen]

Yeah, well that's then true for the penis. The vagina stays where it is and 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. Hours. Yeah. Many snails mate for, you know, two, three, four, five, up to seven hours. I've seen snails mating for an entire night. They usually mate during the night. So can take the whole night for them to get all this process underway.

[Molly Webster]

It reminds me of some sort of like dial up Internet.

[Menno Schildhausen]

Yeah, exactly.

[Molly Webster]

You're like, okay, we're connected now. We're waiting to connect.

[Menno Schildhausen]

Almost as long as setting up this interview took. Yeah, yeah.

[Molly Webster]

Oh my gosh. And they are just connected by these fingers the whole time?

[Menno Schildhausen]

Yes. Again, it depends on the species.

[Molly Webster]

This is really where the evolution of genitalia kicks in.

[Menno Schildhausen]

There are these fingers. They're also sort of tongue like structures. There's one family of slugs that has these with which they lick each other. And these tongues are attached to the penis. There are also species that don't insert their penises into the partner, but they keep the penises dangling on the outside. And the sperm is transferred by sort of a handshake from one penis tip to the other penis tip. There's a species of tiger slug from southern Europe where this happens at the end of a penis that is almost a meter long. So that would be like 25 inches more even. I think that's 2ft no more 35ft. Yeah, yeah, it's 3ft. It's about 3ft. And these. So these are actually contenders for the longest penises compared to body length in the animal world.

[Molly Webster]

Well, yeah, it seems like it would just tip over a slug.

[Menno Schildhausen]

Yeah, well, it's like spaghetti. I mean like cooked spaghetti is very flexible. So they hang from a tree in the. These penises dangle down and they entwine and at the tip of the penis the sperm package is transferred. Oh, so the sperm package is quite large and quite nutritious and it has millions of sperm in it, sperm cells. And it just. 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 digest, is being eaten.

[Cotton Soren Wheeler]

Oh, they can eat the sperm?

[Molly Webster]

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 way to store sperm if they're just.

[Cotton Soren Wheeler]

Is not the right time for me to. I'm working on my snail career and I don't really want to get pregnant.

[Molly Webster]

The up and coming actor. 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.

[Menno Schildhausen]

A duel which involves all these weird organs that they use in their reproduction, like sperm storage organs and sperm digesting organs and dart glands and dart sex. And it's a whole circus of sexual

[Molly Webster]

extravagance that is coming up after the break.

[Cotton Soren Wheeler]

Okay,

[Lulu Miller]

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[Ira Flatow]

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[Molly Webster]

Hey hey. I'm Molly. You're Soren.

[Cotton Soren Wheeler]

Yes. And I think we are about to

[Molly Webster]

have a I promised a duel and a 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.

[Cotton Soren Wheeler]

Love darts?

[Menno Schildhausen]

Love darts. They are produced in an organ called the dart sac. And the dart is a little limestone needle made from the same material as the shell, Shaped like a little dagger.

[Molly Webster]

Oh, really?

[Menno Schildhausen]

Yeah.

[Cotton Soren Wheeler]

Can I google it?

[Molly Webster]

Can I share my screen with you?

[Cotton Soren Wheeler]

Sure.

[Molly Webster]

Screenshot. Okay, ready?

[Cotton Soren Wheeler]

Whoa.

[Molly Webster]

It looks like whittled bone, like, white bone.

[Menno Schildhausen]

It's almost like a tool.

[Cotton Soren Wheeler]

Like you'd imagine. Like, you'd find in, like, an archaeological site was early needles that early humans used.

[Molly Webster]

There'd be, like, early humans crafted this.

[Cotton Soren Wheeler]

Crafted a needle out of bone.

[Molly Webster]

Yeah.

[Menno Schildhausen]

Yeah. Oh, yeah. It's beautiful. If you see.

[Cotton Soren Wheeler]

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

[Menno Schildhausen]

Well, there are species in which the dart looks surprisingly like an arrow you've drawn when you were a kid.

[Cotton Soren Wheeler]

Even, like, the little feathery thing that's in the back of the arrow, there's a little, like.

[Molly Webster]

Yeah, what do they call them? Those are, like, fletchings. Fletchings.

[Menno Schildhausen]

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

[Molly Webster]

One centimeter?

[Menno Schildhausen]

Yeah. So, yeah, that's almost half an inch. They are present in a snail even if they're not mating. And you can feel them crushing when you're eating a snail.

[Molly Webster]

So you'll be, like, eating snails, and then you'll go, oh, just hit a love dart.

[Menno Schildhausen]

Well, I would. Most people wouldn't. They would just.

[Molly Webster]

No, yeah, you. I'm talking about you specifically. Menno.

[Menno Schildhausen]

Yeah. Yes. Yeah. Yes. I would.

[Molly Webster]

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.

[Menno Schildhausen]

Yeah, no, you eat that entire reproductive system as well, including the love dart.

[Cotton Soren Wheeler]

So the dart is not a penis. It's not like delivering sperm.

[Molly Webster]

The dart is not a penis.

[Cotton Soren Wheeler]

Okay.

[Molly Webster]

The dart plays a specific role.

[Menno Schildhausen]

So what they do with the love dart is they expel this dart with considerable force into the partner.

[Molly Webster]

Like, they shoot it.

[Menno Schildhausen]

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 force. And it goes fast. So there's a muscular organ that 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 bottom. Yeah.

[Molly Webster]

And where are you shooting the dart toward, like, what do you want to hit?

[Menno Schildhausen]

It looks like you mostly want to hit the skin very close to that genital opening, but sometimes.

[Molly Webster]

So the head, the face.

[Menno Schildhausen]

Yeah. The cheek.

[Molly Webster]

Okay.

[Menno Schildhausen]

Yeah.

[Molly Webster]

And what is it doing with the dart? Is it shooting a material substance is just like, hey, I want your att?

[Menno Schildhausen]

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 heads. And sharks also do that. So why not shoot a dart? It could be something like that. And then people thought maybe it's what they call a nuptial gift. So a donation of calcium to help the partner build the eggs for the offspring that they're going to produce.

[Molly Webster]

Because eggs use calcium, because the eggs

[Menno Schildhausen]

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 Jolas Kune showed that there were actually hormones being delivered into the body of the snail that is being shot.

[Molly Webster]

Hormones.

[Menno Schildhausen]

Yeah, yeah, yeah.

[Molly Webster]

So the dark gland produces this mucus that has inside of it a. Essentially a sex hormone. And the arrow is either covered in or full of this sticky goo.

[Menno Schildhausen]

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.

[Molly Webster]

Whoa. Okay.

[Menno Schildhausen]

So it's a kind of manipulation.

[Molly Webster]

You're saying that when this hormone hits the system of the partner, what you could call the vagina, and it, like, makes it seize or like, cramp or something?

[Menno Schildhausen]

It's a little bit more complicated than that, unfortunately.

[Molly Webster]

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.

[Cotton Soren Wheeler]

Sounds almost like a. Like a little orgasm or something.

[Molly Webster]

Yeah, but it causes muscles to contract.

[Menno Schildhausen]

And what. What the hormone does is it sort of creates or it causes the entrance of that digesting organ to close off.

[Molly Webster]

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.

[Menno Schildhausen]

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 stab multiple times, and every time they step, the dart is recharged with new hormone. So they have this. They 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 again and push it in again. So there's a snail where this has been seen. So 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. So they just keep pumping this hormone into the partner and vice versa.

[Molly Webster]

And the partner lived through 3,000 stabs?

[Menno Schildhausen]

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.

[Molly Webster]

Did you say it's not like Caesar?

[Menno Schildhausen]

Yes. So, yeah, there's pictures of these snails that are mating, and there's. This dart is sticking through the head of one of the snails. The fletchings are still coming out on one side, and the tip is coming out on the other side.

[Molly Webster]

So they're, like, visible to the naked eye.

[Menno Schildhausen]

Yeah. I find them in my garden after a wet night when snails have been mating. And sometimes they leave those darts on the floor.

[Molly Webster]

Wait, do you think I've seen a snail dart and just not known it could be. And it doesn't kill it?

[Menno Schildhausen]

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 maybe nothing.

[Molly Webster]

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.

[Menno Schildhausen]

I wouldn't be surprised. Yeah, man.

[Molly Webster]

I'm just thinking about you in your backyard just like, picking up love darts. Are you, like, wow, last night was a big night?

[Menno Schildhausen]

Yeah, exactly. It's usually in the spring when it's warm but rainy. When we have spring like that, you see snails mating, and you find these slime spots which are sort of a telltale sign that they've been having fun. And you find these love darts lying on the floor because they do sometimes miss, and sometimes they also expel them from their body after mating.

[Molly Webster]

How would they get it out? Like, if I have a love dart through My head, How am I extracting it?

[Menno Schildhausen]

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 movements, it wiggles out just like a splinter in your skin.

[Molly Webster]

And you as a scientist, I'm assuming that love darts are interesting to you and that finding out how they worked is of interest to you. So I'm just curious as to what insights it gives you.

[Menno Schildhausen]

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 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 have this disposable dart, 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 there'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.

[Cotton Soren Wheeler]

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.

[Molly Webster]

Yeah, it's like, it's like you just look at these things and you think slime ball. You don't think theater of evolution.

[Cotton Soren Wheeler]

No, no. Or three foot penis. Or look at what I'd been missing this whole time.

[Molly Webster]

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. It's so funny to say this to a scientist and I do really believe in science, but 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. And I know that it's real because of that.

[Menno Schildhausen]

Yeah. And of course, there's also these medieval marginalia. I don't know if you've heard about these.

[Molly Webster]

No, what's that?

[Menno Schildhausen]

So marginalia are these little embellishments in the margins of medieval books where, you know, there would be little scenes of a hare or a duck or a fox chasing a bird. But there's also lots of marginalia about knights fighting with snails, with swords.

[Molly Webster]

Really?

[Menno Schildhausen]

Yeah. And people have also thought maybe that has to do with the love darts. There's a whole literature on this, so

[Molly Webster]

it feels like there was almost like a time of the world when we were bumping into love darts.

[Cotton Soren Wheeler]

More?

[Menno Schildhausen]

Mm. Yeah.

[Cotton Soren Wheeler]

Okay.

[Menno Schildhausen]

Oh, my God.

[Molly Webster]

This pet story is busy. Okay, that's that.

[Menno Schildhausen]

Maybe

[Molly Webster]

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?

[Menno Schildhausen]

Yeah, there is, actually. Some people think that's how the myth of Cupid evolved. Wow.

[Molly Webster]

The street stepping over an exploded bag of trash. Wait, so could I go find a love dart?

[Menno Schildhausen]

Well, they're in Prospect park in Brooklyn on trees.

[Molly Webster]

So there are some local love darts, definitely.

[Menno Schildhausen]

You'd have to wait for them to come out of hibernation, which would be in late April, probably.

[Molly Webster]

Okay.

[Menno Schildhausen]

And then they usually start mating quite soon thereafter. So if you have go out early in the morning and look. Yeah. 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.

[Molly Webster]

You've given us a new thing to go into the world and find. The crown's not thawed yet.

[Menno Schildhausen]

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.

[Molly Webster]

There's a wet tree.

[Menno Schildhausen]

And they will.

[Molly Webster]

Not quite yet, but soon.

[Menno Schildhausen]

It's a miniature world that exists.

[Molly Webster]

This would be where you could find a snail or two. This episode was produced by Mona Medgauker, Annie McKeown, 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 Menno's book called nature's nether regions. There's a whole chapter on snail sex. Menno Schilthausen is a evolutionary biologist at Leiden University in the Netherlands. Thank you, Menno. And I also want to give a shout out to Erin 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 [e-mail] 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 snug 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. For now, I am Molly Webster. Spring is a coming this is Radiolab. Thanks for listening. Hi, I'm Gabby. I'm from San Francisco and here are the staff credits. Radiolab is hosted by Lulu Miller and Latif Nasser. Soren Wheeler is our Executive editor. Sarah Sandback 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, Nainasem Bandun, Matt Kielty, Mona McGacher, Annie McKeown, Alex Neeson, Sara Khari, Rebecca Rand, Anisa Vitse, Arian Wack, Molly Webster, and Jessica Young, with help from Gabby Santis. Our fact checkers are Diane Kelly, Emily Krieger, Natalie Middleton, Angeli Mercado, and Sophie Semey. Leadership support for Radiolab's 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.

[Ira Flatow]

This is Ira Flato, host of Science Friday. For over 30 years, the science Friday team has been reporting high quality science and technology news, making science fun for curious people by covering everything from the outer reaches of space to the rapidly changing world of AI to the tiniest microbes in our bodies. Audiences trust our show because they know we're driven by a mission to inform and serve listeners first and foremost with important news they won't get anywhere else. And our sponsors benefit from that halo effect. For more information on becoming a sponsor, visit sponsorship.wnyc.org.