Good Vibrations Key To Insect Communication For some insects, sound waves or vibrations are the real social media — high-speed rumbles sent through the air and along leaf stems to help the bugs claim territory, send warnings and find mates.
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Good Vibrations Key To Insect Communication

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Good Vibrations Key To Insect Communication

Good Vibrations Key To Insect Communication

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STEVE INSKEEP, HOST:

It's MORNING EDITION from NPR News. I'm Steve Inskeep.

DAVID GREENE, HOST:

And I'm David Greene. Good morning.

(SOUNDBITE OF TREEHOPPERS CHIRPING)

GREENE: What you're hearing are treehoppers. These are insects that communicate with each other by making leaf stems vibrate.

(SOUNDBITE OF CRICKETS CHIRPING)

GREENE: And what you're hearing now are crickets, whose chirps contain encoded messages that convey life or death information. Scientists discovered this vibrational world of insects through close listening. That's what we're calling our project on decoding nature through sound. Today, NPR's Christopher Joyce and audio producer Bill McQuay of the Cornell Lab of Ornithology profile two scientists who reveal how these insects manage their complex social lives with sound.

CHRISTOPHER JOYCE, BYLINE: Lots of animals, including ourselves, can feel sound as well as hear it. Elephants, for example, can communicate by rumbling at low frequencies we can't hear - whales too.

BILL MCQUAY, BYLINE: But you don't have to weigh a ton to rumble.

JOYCE: No, in fact, you don't have to be bigger than a pea, like a treehopper, a curious little sap-sucking insect that lives on the stems of leaves. Biologist Rex Cocroft is a researcher at the University of Missouri who studies treehoppers. In 1999, a team from NPR's Radio Expeditions program rendezvoused with him at a locust tree in a backyard in Virginia.

MCQUAY: He was pressing a phonograph needle up against the stem of a leaf.

REX COCROFT: I'm just trying to get a good contact here between the stylus on the phono cartridge and part of the plant. Mind you, this is not in the manufacturer's instructions for these phono cartridges.

MCQUAY: There's no guidebook for listening to treehoppers. Cocroft created his own. He knew that needles in those cartridges are exquisitely sensitive to vibration. So he connected a wire from the cartridge through an amplifier and to his headphone.

JOYCE: And this is what he heard.

(SOUNDBITE OF TREEHOPPERS CHIRPING)

COCROFT: All the signals you're hearing are signals produced by males.

JOYCE: They're vibrating their abdomens at incredibly high-speed to make an assortment of bizarre sounds. Some are for attracting females. And some are aimed at other males.

(SOUNDBITE OF TREEHOPPERS CHIRPING)

COCROFT: We're hearing that kind of purring (imitating treehopper sounds) sound - are sounds that males give either when two males meet each other or when they're mate-searching on a branch.

MCQUAY: Normally, we can't hear any of this. The sound travels inside the stem.

JOYCE: So how did such a weird insect telegraph evolve? Well, Rex says treehoppers, like many insects, have very sensitive legs. And they stand around on stems, which are good at transmitting vibrations. So they used what nature gave them. It gave them a way to communicate. And as a social animals, that's what they need to thrive.

COCROFT: They have so many different forms of social behavior and grouping. And once you have animals living in groups, then you have all sorts of interesting possibilities for communication.

(SOUNDBITE OF TREEHOPPERS CHIRPING)

JOYCE: Such as scouts tapping out a signal to others that there's a predator nearby.

MCQUAY: Technology revealed this hidden vibrational world, things like phonograph needles and devices called accelerometers that measure vibration. And that ushered in a new generation of insect eavesdroppers.

LAUREL SYMES: So I'm here tonight in Fort Worth, Texas.

JOYCE: Like Laurel Symes, a biologist at Dartmouth College. Symes tunes into vibrations we can hear made by crickets.

SYMES: So now we're looking at a male tree cricket. So the way that the cricket makes sound is to use its wings. And if you look closely at one of the wings, it has a whole bunch of little tiny teeth on it. And that rubs against a vein on the other wing and it causes the whole wing to vibrate sort of like a drum head would.

JOYCE: Crickets don't have a big vocabulary like treehoppers. What they do have is a remarkable ability to discriminate tiny differences in sound frequency, a skill worthy of a concert violinist. It's the females that can do this. And the reason - Bill, you want to explain that?

MCQUAY: So you go out in the woods and you hear crickets chirping. They're males of several species all saying come and get me. To us, they sound pretty much the same, but they aren't. The speed at which they rub their wings together, the pulse rate, varies from species to species. And Laurel discovered that females know that.

SYMES: And they've evolved to be very, very good at recognizing the exact thing that they're looking for.

JOYCE: Which is the pulse rate of a potential mate from their own species. And there's a good reason to be very picky.

SYMES: If you don't get it right, you lose.

JOYCE: You lose if you pick the wrong species of male to mate with. You won't make little crickets.

MCQUAY: Laurel actually rigged up a clever experiment to test how good the females were. She synthesized the chirps of various male crickets on a computer. They were identical to the real sound and she played them for two species of females through a speaker. Here's one chirp, a male at 43 pulses per second.

(SOUNDBITE OF CRICKET CHIRPING)

MCQUAY: The females of one species immediately hustled over to the loudspeaker. The other females - not interested. Then Laurel used this chirp at 51 pulses per second.

JOYCE: Just eight pulses a second faster than the first one.

(SOUNDBITE OF CRICKET CHIRPING)

JOYCE: And the females of the other species, the one that ignored the first sound, they got all romantic with the speaker. So what's happening is that each species of cricket, there are about 140 in North America, has divided up the sound spectrum into sonic niches. Each species identifies with its own frequency like a radio station. And they do it with a brain the size of a pin head.

SYMES: And that's one of the things that makes them cool is they have really simple sensory systems and still they parse this really complex world.

JOYCE: Symes spent years recording crickets to figure all this out. She goes wherever they are like up a tree on the Mexican border where border patrol agents wondered just what the heck she was doing.

SYMES: You're part way up a tree and, you know, the vehicle pulls up and stops and they flip on their light, you know - what are you doing out here tonight, ma'am? Oh, I'm just collecting crickets. They believed me; that's what amazed me.

JOYCE: Now she's so tuned into the cricket world she thinks and sounds like them.

SYMES: (Imitating cricket) That's about 60.

MCQUAY: Yes, Laurel can do 60 pulses a second herself. She says it's a lot like a humming refrigerator.

JOYCE: In fact, she's always listening to vibrations, crickets, fans, air-conditioners.

SYMES: We think that we really know what's going on out there and we're getting this tiny slice of all of the sound in the world.

JOYCE: As for Rex Cocroft, he says most of this sonic world still remains to be discovered.

COCROFT: It's a very intense world and so little of it really still has ever been listened to that it's very possible for anyone to go out into a weedy field or roadside and tap into those plants and hear very interesting sounds that no one has ever heard before.

JOYCE: Sounds shaped by millions of years of evolution and the struggle to survive. I'm Christopher Joyce, NPR News.

MCQUAY: And I'm Bill McQuay.

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