'Sex On Six Legs': When Insects Go Wild Everything you wanted to know about bug sex (but didn't bother to ask) is explained in a new book. Insect expert Marlene Zuk describes how ants learn, why some crickets don't chirp and how various bugs mate in Sex on Six Legs: Lessons on Life, Love and Language from the Insect World.
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'Sex On Six Legs': When Insects Go Wild

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'Sex On Six Legs': When Insects Go Wild

'Sex On Six Legs': When Insects Go Wild

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This is FRESH AIR. I'm Dave Davies, in for Terry Gross.

Our next guest, Marlene Zuk, can get a little defensive on the subject of insects. She's a biology professor at the University of California, Riverside, who spent years studying animal behavior. She says while everyone loves watching eagle's nests or observing the social behavior of chimps, fewer appreciate the complex behavior of our six-legged friends.

It her new book, she says there's evidence that some insects - including ants and wasps - display individual personalities and learned behaviors not embedded in their genetic code, and that insects show parenting skills and mating rituals that are simply amazing.

Marlene Zuk has written two previous books and articles which have appeared in several publications, including The New York Times. Her new book is called "Sex on Six Legs: Lessons on Love, Life and Language from the Insect World."

Well, Marlene Zuk, welcome to FRESH AIR. You write in this book that insects bring home the uneasy truth that you don't need a big brain to do big things, like, for example, learn from others. Can insects learn? Do we see this?

Ms. MARLENE ZUK (Biologist, University of California Riverside): Yeah. Insects can learn a lot more than people give them credit for. I think one of the things I tried to do in the book is to counteract this image people have of insects as mindless robots that march around driven by instinct and don't actually respond to their environment.

But it turns out they learn all kinds of things. They can - and in fact, not only can they learn, for instance, where their food is or to avoid noxious stimuli, they can even teach each other. So they can teach another insect what to do, which is a really extraordinary accomplishment that not a lot of other animals - even vertebrates as we often think of as pretty smart - can do.

DAVIES: Okay. Well, give us an example. I mean, how do we know we're not looking at simply a behavior that's embedded in their genes?

Ms. ZUK: So, with the learning, it's a behavior that's called tandem running in ants. It doesn't look usually dramatic, I will confess. But still, it means that an ant who's found a food source will come back to recruit others to go to the same food source. And anybody who's ever had ants running around their kitchen knows that, you know, you get this trail. You don't just get one ant going back and forth.

Well, the other ants find out where to go not just from the odors that the first ant leaves when it goes back - when she goes back and forth, but also because an ant will find a nest mate and kind of run along beside her, sort of encouraging her where to go.

One of the researchers that did this work says that it looks like a parent teaching a child how to ride a bicycle, you know, where you're kind of going along next to them and along next to them, and you have your finger kind of - or your hand on the seat kind of guiding them along.

And so they do this and steer the other individual, showing them where to go, and will actually wait for them to catch up and make sure they're going the right direction, and so forth - which, like I said, doesn't look very dramatic. It looks like two ants walking together. But in actual fact, it's teaching. But on top of that, there's at least some social insects that can recognize minute differences in facial appearance, just the way we would.

There are wasps that can determine which individual is which based on really subtle distinctions in the black-and-yellow patterning they get on the head, just like, you know, you look at someone and look at the relative, you know, width of their nose and their eyebrows and so forth and can tell different people apart, they can do a very similar kind of thing.

DAVIES: You know, this is a fascinating experiment that you describe, in which somebody actually captures these insects and does a little face painting on them.

Ms. ZUK: Yeah.

DAVIES: I could only imagine how this is accomplished. So they put markings on the faces of...

(Soundbite of laughter)

DAVIES: ...these - what are they, wasps, or...

Ms. ZUK: They're wasps. Yeah. They're wasps.

DAVIES: Yeah. And then what did they observe? How did they know that they were - that the wasps were really making these distinctions and the subtle differences?

Ms. ZUK: So you can put to wasps together, and they'll interact in a way just like say dogs would, where one of them will become kind of the top dog and one of them will become the subordinate. And there's really characteristic behaviors where you can notice that happening. And the same thing with wasps. You just need to know what to look for. You know, you could do this with any animal, where then you'd say all right, well, how are they telling? And then afterwards, they'll behave just exactly, you know, as if they remember who was dominant and who wasn't dominant when they were interacting before. So they'll, you know, if you put them together again, the one that had won the fight will be dominant and get, say, access to food and so forth.

Well, if you take the one that was previously subordinate and you paint it to look dominant, or you take the one that was previously dominant and paint it to look subordinate, you end up with a slight change in behavior. So it's like they'll look at each other and kind of stop, as if you saw your friend wearing a mask. And some things about it looked familiar, but wait a minute, the face is wrong. You look different. And the wasps have a really similar sort of reaction, where they kind of stop and don't behave as though they would to the same individual.

I mean, the actual mechanics of doing this, yeah, I mean it is a little funny, and you do spend a lot of time, you know, working with really tiny things. And people who work with stinging insects do have special ways to not get stung and so forth. But...

DAVIES: Okay. You've just got to tell me: How do we take a wasp then give it makeup?

(Soundbite of laughter)

Ms. ZUK: You need to have a very calm wasp, a very calm wasp. Often you can either anesthetize insects - there's a couple of short-acting chemicals you can use, essentially, you know, giving them anesthesia. Or you can chill down insects, and that often slows them down enough that you can do things like that, too. Because remember, insects are cold-blooded. And so anytime you put them in a cold environment, they kind of go into suspended animation. So a lot of people who work with insects do that, too.

But the other thing is - and again, this speaks to kind of the insect-phobia that I also talk about in the book, that insects are really not out to get you. Certainly, if you pick up a wasp and start messing with her, then yes, she's probably likely to want to sting you if you're not careful. But by and large, it's not like you're constantly having to defend yourself against these, you know, horrible, aggressive insects that if you're not careful will try to, you know, bite your hand off or something. So...

DAVIES: You study crickets a lot, right?

Ms. ZUK: I do.

DAVIES: And you have a fascinating story about going into Hawaii and discovered there are crickets there who are quiet. What was going on, and why was that interesting to you?

Ms. ZUK: So we've been working for a long time on a species of cricket that's common all through northern Australia and the Pacific. It's sort of subtropical. It's been introduced to Hawaii. And in Hawaii, I stumbled on this really interesting relationship where the crickets are subject to a parasitic fly. And so the fly can hear the crickets calling, and crickets, of course, call to attract mates. So all the chirping you hear outside when you go outside on a summer night, all of that nice, melodious sound is male crickets desperate for sex.

Obviously, that's very important for evolution, because the more they sing, the more they're going to attract females, and therefore, the more they're going to pass their genes on. That's fine.

The problem in Hawaii is that these crickets also, by singing, attract the attention of a parasitic fly. The fly can hear the song as well or better than a female cricket. She flies over. The female fly goes over to the cricket, deposits these larvae on and around it. The larvae burrow inside the cricket while the cricket's still alive and live, there consuming his tissues for a week or so while he's gradually getting weaker but, you know, is still functioning. So it's like they've got preserved food to eat, the larvae of the fly do.

And then eventually after about a week, they burst out, just like the movie "Alien," and kill the cricket, and then the fly pupates in the soil and then becomes an adult fly.

I got interested in this because, from an evolutionary perspective, it's the perfect conflict. The more the male calls, the better it is from an evolutionary perspective, because the more females he's going to attract. So it's a good thing.

But the more the male calls, the more flies he's going to attract, which is going to kill him, which is obviously a bad thing. And yet it's the same call that's attracting both kinds of insects. So how does evolution sort out these conflicting selection pressures? And so we've been studying there for quite a long time.

The silent cricket that you just mentioned has been a really recent and really exciting development, which is that we noticed on one of the islands where the crickets occurred, we were finding fewer and fewer individuals and we couldn't, you know, here as many. I keep them in my lab, and I couldn't find as many females to lay eggs for my lab colony.

And eventually, I thought, okay, they're just going to go extinct. This is actually an introduced species with an introduced parasite, and sometimes that's unstable. So, all right, never mind, you know, these things are dynamic, and they're just going to go extinct eventually.

But one day we came back, and I didn't hear any crickets at all, but started to go to the field site anyway, figuring, you know, you may as well see if there's anything around. And I started seeing lots and lots and lots of crickets. So there were many more there than had been before, but none of them were making a sound. It turned out that they were not making a sound not because they were behaviorally refraining from it, that it wasn't that they didn't want to, it was that they couldn't. Their wings now show this mutation that renders them completely silent.

DAVIES: So it protects them from the parasite. But what do they do for sex?

Ms. ZUK: Ah, yes. Exactly. I mean - and it does protect them from the parasite, because the fly can't find them if they can't call. But, of course, then the female shouldn't be able to find them, either.

It turns out that it's not all the males that show this mutation. About 10 to 15 percent of the male are still normal-winged callers, as per usual. And those can attract females just like any male could. The silent males, the ones that now have this mutation, get very close to the callers, hang around them, and in so doing, kind of take advantage of the females that are attracted to the callers and can mate with them as they move toward the singing males.

DAVIES: There's a lot of interesting stuff in this book about sex, reproduction, mating. And you found that the competition among males to reproduce has some interesting manifestations, and in many cases, that competitions - occurs after they mate. They have these particular physical adaptations to make theirs the sperm that does the job. Give us an example or two of this.

Ms. ZUK: Sure. Insects are a great way to study how sex isn't really over when it's over. People tend to think that after mating has happened, well, since you can't see anything, then that must be it and everything is just finished. But an insect - and as it's turning out in lots of other animals, but insects are a great way to study this, if a female insect mates with more than one male in pretty rapid succession, as lots of insects do, then there's an opportunity for the sperm of those males - so the males themselves are long gone. But there's an opportunity for the sperm of those males to compete inside the body of the female in a process that's called sperm competition. And males have lots of tricks that they use to get their sperm to fertilize the eggs rather than another male's.

So, for example, in damsel flies, they've got these special scoops on the intermittent organ the penis, in effect, of the male - that they can use to drag out the sperm from a previous male and replace it with their own.

DAVIES: Wow. And what's the evolutionary value of that? Why would a species in which males have that ability be more likely to survive? I mean, why would one individual's sperm be better than another? Why is that better for the survival and propagation of the species?

Ms. ZUK: It's not that it's necessarily better for the species as a whole, but pretty much everything we see in evolution happens because it perpetuates the individual genes that are, you know, doing whatever it is. So, no, it's not necessarily better for the species, but it means that if I am able to displace the sperm of another male, then the genes, for being able to displace the sperm of another male, are going to be the ones that fertilize the eggs of the female that I just displaced the sperm from another male in. And so her offspring are all going to be able to displace sperm. Well, guess what happens? You end up with a population in which everybody can do this, and there's competition among males to do it the best.

DAVIES: Now there are also ways in which males try and get females to accept their sperm, right? Some fascinating examples of that.

Ms. ZUK: In a lot of Orthoptera like crickets and katydids and their relatives, males produce sperm that's external. It's in a little package called the spermatophore. But in the species, it's attached to what is called a spermatophylax, which is this big, globby thing that is - has a lot of protein in it. It's very nutritious. And the female eats it while the sperm are draining into her body.

Now the males have to produce this before the female will mate. If he just goes up to her and jut has the little sperm package, she won't mate with him. If he gives her the spermatophylax, she will mate with him, but the bigger and more nutritious it is, the longer she spends eating it, and therefore the more of his sperm drain into her body and fertilize her eggs. So there's a lot of selection on males to produce this very costly - what's called a nuptial gift. And it can often weigh up to 30 percent of the male's body weight.

DAVIES: Marlene Zuk's new book is called "Sex on Six Legs."

We'll talk more after a short break.

This is FRESH AIR.

(Soundbite of music)

DAVIES: If you're just joining us, our guest is biologist Marlene Zuk. Her new book is called "Sex on Six Legs: Lessons on Life, Love and Language from the Insect World."

There's some remarkable stuff in here about parenting, taking care of eggs, raising kids. And it's interesting to discover that there are plenty of cases where the dads take care, right?

Ms. ZUK: Oh, absolutely. And let me point out that insects make great parents. One beautiful example that if people go out to streams and rivers in - especially in parts of the American Southwest that they can see - are giant water bugs. And giant, of course, is a relative term. They're probably, oh, I don't know, maybe a little bit bigger than a dollar coin or something like that, which is, you know, big for a bug. And they live streams.

And the males actually carry around the eggs on their back for the whole time that the eggs are incubating. And then when they hatch, sometimes they'll take care of them a little bit more. Sometimes they'll just let them go. But the moms just lay the eggs on the back of the male and then swim off and never a care in the world.

DAVIES: Any idea why that happens?

Ms. ZUK: It's kind of a hard road to hoe for fathers to be the main caregivers because, of course, in insects, as in lots of other animals, it's never entirely certain that the father is actually the father of the offspring that come out of the eggs that the female laid, because, of course, the fertilization happened inside the body of the female. And so she can lay these eggs and you can have mated with her, but what if she mated with somebody else? And so this is called certainty of paternity, and it means that - in some cases, at least - there's not a lot of payoff for males to take care of their babies, because the babies might not really be genetically theirs.

In the case of the water bugs, though, it's very clever, because the female puts the eggs on the males' back before they're fertilized. And so then the male can put his sperm on them, and they're absolutely certain to be his.

DAVIES: Now, you also find cases where insects eat their babies, or at least their eggs. Give us an example, and tell us why this makes evolutionary sense.

Ms. ZUK: Again, it's one of these things where sometimes doing something that seems drastic in the short-term but pays off in the long-term is really a good idea. For example, if you have a lot of eggs and the breeding season is kind of going on and on, you're not able to find a lot of food for yourself, you're going to be better off by eating some of those eggs, consuming them. And so, of course, they'll survive, but the ones that remain will get the protection that you can give them by hanging on long enough to take care of them. So it's a way of sacrificing the few for the sake of the rest.

DAVIES: And we also see siblicide, right? I mean, young coming out and eating their brothers and sisters.

Ms. ZUK: Oh, absolutely. And, in fact, it is often kind of a larva-eat-larva world out there. So if - again, if insects are all in the same place or if the babies are all in the same place, then the first one that hatches will often have, as its first act, consuming an egg that's next it that hasn't had the good fortune to hatch yet. And so siblicide turns out to be quite common. And again, it's one of these things where if you can pass your genes on better by doing it, then that's just what's going to happen.

DAVIES: Now, you also have this fascinating chapter on communication among insects. And you cite an example of how bees who - where a hive has gotten big and a portion of the bees in the hive were going to go out and start a new one will collectively scout out a location and then communicate, in effect, kind of have a debate and a decision about where they're going to go. Describe this.

Ms. ZUK: So this is one of the most, I think, understudied and remarkable things that insects can do. We talk about the complexity of behavior, they have complex decision-making. And you, you know, you can liken it to finding a new place to live. Imagine if every time you found a new house, you had to find it with thousands and thousands of, you know, your friends and relations. Well, in this case, it's all your relations, but, anyway. And you all had to agree on exactly where to go, exactly when to go there and how to find your way.

So bees seem to be able to do this by sending out scouts. So they'll send out a few individual - when a hive is ready to split, they'll send out a few individuals that will go looking for an appropriate place to live and then come back and perform a dance behavior that indicates where this place might be. And by sort of putting the various dances together that different individuals do, the bees are actually able to come to a consensus about where they're going to go. And then once they've reached that consensus, they all go there. And this is an amazing ability, again, because their brains are so small.

And this is one of the reasons that insects are so cool to study, that we think decision-making is a tremendously complicated thing. It requires, you know, your forebrain. It requires your cerebral cortex. It requires all this gray matter. Bees don't have any of that, and yet they seem to be able to do exactly the same thing. One of the people studying the bees said, you know, it makes you wonder: What are we doing with our brains? What are they for?

(Soundbite of laughter)

DAVIES: Well, just to be clear about this, we're talking about a case where the dance isn't about - isn't one bee describing a single, you know, new location for a potential hive. There are actually multiple locations that are being described through...

Ms. ZUK: Each dancer will describe its own - each dancer will describe...


Ms. ZUK: ...a place where it has been, and then eventually the hive sort of weighs all of the various places and goes to one of them. And exactly how they do this and exactly what the criteria are for going for one place over another is still really, you know, being studied right now by lots of scientists.

DAVIES: Well, Marlene Zuk, it's been interesting. Thanks so much.

Ms. ZUK: Thank you.

DAVIES: Marlene Zuk's book is called "Sex on Six Legs: Lessons on Life, Love and Language from the Insect World."

Coming up, Maureen Corrigan on a disturbing novel about childrearing in the digital age.

This is FRESH AIR.

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