Marlene Zuk: What humans can learn from the sex lives of insects Insects experience the world very differently from humans--but they still have a lot to teach us. Behavioral ecologist Marlene Zuk explores what insects can teach us about sex and sexuality.

What humans can learn from the sex lives of insects

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We've been hearing about animal instincts, behaviors that are crucial to survival, because it can be tough out there. Take the lowly cricket, for example.

MARLENE ZUK: From a cricket's standpoint, the world is very big and very dark.

ZOMORODI: This is Marlene Zuk. She's an evolutionary biologist and behavioral ecologist who specializes in insect reproduction.

ZUK: The short version I always tell people is I study bug sex.

ZOMORODI: And Marlene has spent a lot of time observing how crickets do it.

ZUK: They're cool to study from the standpoint of understanding how males and females interact because, as everybody knows, crickets sing, and the song attracts females from a distance.

ZOMORODI: This cricket story begins when Marlene was invited to a conference in Hawaii 20 years ago, and she spent a couple extra days researching male-female cricket interaction.

ZUK: It's not clear to me why I couldn't come up with the standard things that one does when one goes to Hawaii. Like, you know, I want to go to the beach, or I want to, you know, go hiking, or I want to, you know, learn to hula. I don't know. And instead, I thought, I wonder if there are crickets that I can look for when I'm in Hawaii.

ZOMORODI: Wait, so how does one collect crickets...

ZUK: (Laughter).

ZOMORODI: night in Hawaii?

ZUK: Or anywhere else. It's a very low-tech operation.


ZUK: So you go outside at night, and you listen for cricket song. You do have to know what they sound like. And, of course, each species has its own song.


ZUK: There is a certain amount of skill involved in sound localization. So if you hear a sound, if you turn your head back and forth, that's actually a good way to figure it out. And it'll be louder on the side where, obviously, the sound is coming from. So...


ZUK: And then, you have to just kind of pounce with your hand, but they don't bite. And it's OK. And so you can just grab them.

ZOMORODI: Marlene was looking for the Pacific field cricket. And that first night, she went out into an open area and noticed that something was off.

ZUK: Unlike the usual situation with crickets where they are all buried under the leaf litter in the grass, I was seeing a bunch of males just walking on top of the lawn.

ZOMORODI: She had heard of only one instance where crickets behaved like this - a case in Texas.

ZUK: Where a scientist named Bill Cade had discovered a parasitic fly that could hear the sound of the cricket and would home in on that cricket and drop its larvae on them. And the larvae then burrow into the cricket, eat it from the inside out...


ZUK: ...And kill the cricket, which is a gory but wonderful life history. And I said, but that's weird because I've never heard of that happening anywhere but in Texas. And then, I was collecting the crickets and dissecting them the next day, and what should happen but a fly larva pops out. And I thought, oh, my God.


ZUK: It turned out that I discovered that there was these sound-orienting parasitic flies in Hawaii that no one had ever known were there. And so that puts the male in this terrible bind because the more he calls, the more likely he is to attract a female, which is the best thing ever from an evolutionary standpoint. But it's also the worst thing ever because he could attract this fly that will deposit these alienlike creatures that will burrow in, eat him...


ZUK: ...From the inside out, and then leave him a shell of his former self.

ZOMORODI: In a minute, more from Marlene Zuk about how these crickets found a genetic loophole and completely changed their reproductive strategy. On the show today, The Birds And The Bees. You're listening to the TED Radio Hour from NPR. Stay with us.


ZOMORODI: It's the TED Radio Hour from NPR. I'm Manoush Zomorodi. On the show today - the birds and the bees. And we were talking to evolutionary biologist Marlene Zuk. She is the author of numerous books and essays.

ZUK: "Riddled With Life: Friendly Worms, Ladybug Sex, And The Parasites That Make Us Who We Are."

"Bring On The Aerial Ant Sex."

"Mates With Benefits: When And How Sexual Cannibalism Is Adaptive."

"Sex On Six Legs: Lessons On Life, Love And..."

ZOMORODI: In addition to writing, Marlene does a lot of field research. And about 30 years ago, she stumbled upon an evolutionary dilemma for the Pacific field crickets of Hawaii.

ZUK: And it turned out that I discovered that there was these sound-orienting parasitic flies in Hawaii that no one had ever known were there.

ZOMORODI: Year after year, Marlene returned to the island of Kauai to see if these crickets could survive an infestation of parasitic flies...

ZUK: That could hear the sound of the cricket and would home in on that cricket and drop its larvae on them, and the larvae then burrow into the cricket, eat it from the inside out and kill the cricket.

ZOMORODI: OK, so if it sings - if the male cricket sings, he could either attract a girlfriend or a murderer.

ZUK: Right. There you go.

ZOMORODI: OK, so how did you go about measuring or observing how the crickets were coping with this?

ZUK: We've been working on three islands in Hawaii. And on one of them, the island of Kauai, the cricket numbers had just been falling for a few years, and I thought, well, you know, maybe we're just going to see extinction happening. And then the following year I went and didn't hear anything but thought, OK, well, you may as well get out of the car. And I started walking up the road where we usually see them in Kauai with my headlamp. And all of a sudden, I started seeing all these crickets, but I wasn't hearing anything.

It's like this moment of cognitive dissonance because if you see crickets and it's nighttime, then you should be hearing crickets. And if it's nighttime and you're not hearing crickets, then you shouldn't be seeing crickets because that's what crickets do. It's their raison d'etre. You know, they call. I mean, that's what male crickets do. And so I literally was picking them up and thinking, what is this? And, you know - 'cause of course, I've been working on them for years by then, so of course I knew what they were. I just couldn't figure it out.

And finally, what we realized is that - not all, as it turns out, but a bunch of the males on that island - and then later it was on other islands as well - had a mutation in their wings that made them unable to call. These male crickets were certainly males, and they, you know, had everything else that a male needs. But their wings looked like female wings, and females don't call. And so this is awesome for the males because it protects them completely from being found by this parasitic fly 'cause the fly can only hunt by listening. But it's also a hindrance because, of course, from the standpoint of, you know, finding a female, they're kind of out of luck.

ZOMORODI: Yeah. Like, what's - yes, they're surviving. They're not being eaten from the inside out by these parasites. But how are they finding females and making more crickets?

ZUK: It turns out that the males with this mutation act as what are called satellites to the calling males.


ZUK: The key to all of this is it can't work unless there's still a few callers because if everybody becomes what we call a flat-wing - one of these males that can't call - then the show is over because everybody's just wandering around in the dark, and nobody can find anybody else. But if there's a few callers left, the females are still super attracted to them. And if, as they're walking toward the caller, they're intercepted by one of these flat-wings, they will, at least some of the time, mate with them. And even if the females don't like them as much, because those flat-wing males are protected from the fly, they live longer. So they can just kind of wait it out. And so even if, on a sort of per-night basis, they're not mating as much, if they live longer, eventually something, you know, will happen to them.

ZOMORODI: So how does this example challenge what we think we know about evolution and how it works?

ZUK: You know, everybody always thinks, oh, evolution - the dinosaurs rose and fell. It's millions of years, and so evolution can't happen fast. But increasingly, scientists are realizing that evolution can happen really fast or really slow or in between, but it's hard to demonstrate in the wild because you're not always there to see it happen. And in our case, because I'd been working on the crickets long-term, I knew that it had taken at maximum about 20 generations to have the mutation spread, which of course, from an evolutionary perspective, is really, really, really fast. And I think that one of the fun things that's come out of a lot of this work is how flexible insect behavior is.

ZOMORODI: Here's Marlene Zuk on the TED stage.


ZUK: Now, I will maintain, and I think I can defend, what may seem like a surprising statement. I think sex in insects is more interesting than sex in people.


ZUK: And the wild variety that we see makes us challenge some of our own assumptions about what it means to be male and female. Of course, to start with, a lot of insects don't need to have sex at all to reproduce. Female aphids can make little, tiny clones of themselves without ever mating - virgin birth right there on your rosebushes.


ZUK: When they do have sex, even their sperm is more interesting than human sperm. Dragonflies and damselflies have penises that look kind of like Swiss Army knives with all of the attachments pulled out.


ZUK: And they use these formidable devices like scoops to remove the sperm from previous males that the female has mated with.


ZUK: So what can we learn from this? I mean, I...


ZUK: All right. It is not a lesson in the sense of us imitating them or of them setting an example for us to follow. What I think insects do is break a lot of the rules that we humans have about the sex roles. So people have this idea that nature dictates kind of a 1950s-sitcom version of what males and females are like so that males are always supposed to be dominant and aggressive, and females are passive and coy. But that's just not the case.

So, for example, take katydids, which are relatives of crickets and grasshoppers. The males are very picky about who they mate with because they not only transfer sperm during mating, they also give the females something called a nuptial gift. Now, the male manufactures this from his own body, and it's extremely costly to produce. It can weigh up to a third of his body mass. I will now pause for a moment and let you think about what it would be like if human men, every time they had sex, had to produce something that weighed 50, 60, 70 pounds.


ZUK: OK, they would not be able to do that very often.


ZUK: And indeed, neither can the katydids. And so what that means is the males are very passive about mating whereas the females are extremely aggressive and competitive in an attempt to get as many of these nutritious nuptial gifts as they can.


ZUK: These nuptial gifts contain protein and a bunch of other nutrients, and the female eats it while she is being fertilized by the male.

ZOMORODI: She's basically eating a PowerBar while they do it.

ZUK: I like to think of it more as, like, a box of, like, really good chocolate truffles, so...

ZOMORODI: OK, yeah, that's better.

ZUK: So I would be, you know - I mean, yes, the protein. But, you know, from her perspective, it's really - it's just a fabulous thing to eat because it helps her produce more eggs, which, of course, makes her produce more offspring, which, of course, makes her produce more genes in the next generation, which, of course, is what it's all about. And so from the standpoint of, like, OK, we've always got these competitive males and these picky females, the katydids don't really follow that rule. They're still male katydids and female katydids, they're - it's not like - they're not changing sex. It's just that being a male and being a female is way more variable than people tend to think.

ZOMORODI: So this might be kind of a dumb question, but I have to ask it. Do you think, Marlene, that insects - I mean, they're hot for each other 'cause they need to procreate.

ZUK: (Laughter).

ZOMORODI: That's in their biology.

ZUK: Sure.

ZOMORODI: But is there a pleasure element in that as well? Or would that just be an example of us anthropomorphizing them?

ZUK: So I think it's a super good question. I don't think it's dumb at all. And I think I - it gets to something that has fascinated me forever, which is, so how much can we think of other animals as being like us? You know, we're fascinated with this. We're like, only humans can, you know, fill in the blank. For a long time, it was use tools. And then, it's like, oops, there's lots of other animals that can use tools.

People are constantly trying to come up with something that will make us different. And then, if it turns out we're not different, then they're all in a tizzy about, oh, but - so does that mean that everything is exactly like us, and they all feel the same things we do, and they all, you know, like, love the way we do? And this is finally getting back to your question - do they all experience pleasure the same way we do? And that explains, you know, everything? And I just don't see why we have to have it one of two ways.

It seems to me that insects and other animals can be not like little automatons or robots or whatever, but they can also not be like us. And it's like we don't expect other animals to be like us physically. Like, we think kidneys are different in different animals. Why do we think that emotions have to be the same in us as in other animals? So I think it's fine. Like, insects have a really weird version of kidneys. They're called malpighian tubules. They do strange stuff. They don't look anything like a kidney, but they have the same function. We have kidneys. Nobody's, like, having hysterics about, but why do we have such different ways to process waste? And, you know, like, it's just - you do you.

This is why I like insects, is because you cannot look at an ant and say, oh, that's just like a person in an exoskeleton because their brain is, like, the size of a poppy seed. I mean, come on. They cannot...

ZOMORODI: (Laughter).

ZUK: ...Be doing the things the way you're doing them because you're doing them dependent on this gigantic, floppy thing inside your skull that then connects to all your nerves and all these - they can't be doing it. And so they're, like, showing you this other world that is completely different.


ZOMORODI: That was evolutionary biologist and behavioral ecologist Marlene Zuk. Her latest book is called "Dancing Cockatoos And The Dead Man Test: How Behavior Evolves And Why It Matters." On the show today, The Birds and The Bees.


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