Amy Martin: 00:00:00

We're in eastern Tennessee half a billion years

Amy Martin: 00:00:03

ago. The land we now call the Smoky Mountains is almost

Amy Martin: 00:00:09

totally covered by a shallow sea, and life on Earth is still

Amy Martin: 00:00:13

mostly confined to the oceans, until a tiny moss does something

Amy Martin: 00:00:20

remarkable. It finds a foothold on some rocks and stays there.

Amy Martin: 00:00:29

It's an early pioneer into the barren world above the waves, an

Amy Martin: 00:00:34

adventurer that helps to turn the terrestrial world green. Now

Amy Martin: 00:00:42

fast forward hundreds of millions of years to 1946. Just

Amy Martin: 00:00:48

down river from the very spot where that ancient moss lived

Amy Martin: 00:00:53

and died, another Trailblazer is born.

Dolly Parton: 00:00:56

Sitting on the front porch on a summer

Dolly Parton: 00:01:00

afternoon.

Amy Martin: 00:01:02

Dolly Parton.

Dolly Parton: 00:01:03

In a straight back chair on two legs, leaned

Dolly Parton: 00:01:08

against the wall.

Amy Martin: 00:01:10

Raised in a one room cabin with 11 siblings, Dolly

Amy Martin: 00:01:14

went on to write thousands of songs, many of them full of

Amy Martin: 00:01:18

references to the wild things she grew up with. This one

Amy Martin: 00:01:22

called "My Tennessee Mountain Home" recounts a childhood

Amy Martin: 00:01:25

filled with butterflies, birds, wildflowers and crickets.

Dolly Parton: 00:01:34

In my Tennessee mountain home, crickets sing in

Dolly Parton: 00:01:39

the fields nearby.

Amy Martin: 00:01:45

So when a geologist unearthed that ancient moss near

Amy Martin: 00:01:49

Dolly's home and learned that it might be one of the oldest

Amy Martin: 00:01:52

fossilized land plants ever discovered, he named it

Amy Martin: 00:01:56

Dollyphyton boucotti in her honor. A moss and a musician, a

Amy Martin: 00:02:05

plant and an animal. This connection between flora and

Amy Martin: 00:02:09

fauna is fundamental to the soundscape of our planet and the

Amy Martin: 00:02:13

flourishing of life overall. Because as plants began to

Amy Martin: 00:02:18

emerge out of the sea, some adventurous animals followed

Amy Martin: 00:02:22

suit. They were probably scorpion-like creatures.

Amy Martin: 00:02:26

Arthropods, related to our modern insects and spiders, and

Amy Martin: 00:02:31

they were the very first animals to scuttle across the untouched

Amy Martin: 00:02:35

beaches of the terrestrial world. This new realm must have

Amy Martin: 00:02:40

been shockingly bright and dry for the plants and the animals,

Amy Martin: 00:02:45

but finding no other life, they went forth and multiplied and

Amy Martin: 00:02:51

multiplied and multiplied. After the mosses and lichens came

Amy Martin: 00:02:56

ferns and trees, and about 150 million years ago, came the

Amy Martin: 00:03:01

miracle of flowers, painting the world in color and pollinated by

Amy Martin: 00:03:07

beetles, moths and other winged things. And as the world got

Amy Martin: 00:03:12

greener, it got louder. Cicadas called from the branches,

Amy Martin: 00:03:16

crickets made choruses in the leaves. Insects invented song.

Amy Martin: 00:03:24

They laid down the very first notes of what would later become

Amy Martin: 00:03:27

a symphony of terrestrial sound. But they couldn't have done it

Amy Martin: 00:03:31

alone. Without plants, there would be no animals, no songs at

Amy Martin: 00:03:36

all. So without Dollyphyton, there might never have been a

Amy Martin: 00:03:42

Dolly Parton. Welcome to Threshold, I'm Amy Martin, and

Amy Martin: 00:03:50

in this episode, we're going to explore the intertwined acoustic

Amy Martin: 00:03:53

lives of plants and insects.

Amy Martin: 00:04:20

So I want to start by naming the dung beetle in the room here.

Amy Martin: 00:04:24

Both plants and insects are things that people often ignore.

Amy Martin: 00:04:29

We just take it for granted that plants spend their lives giving

Amy Martin: 00:04:32

us breathable air, stabilizing our climate and providing the

Amy Martin: 00:04:37

basis for every bite of food we consume, and we forget that

Amy Martin: 00:04:42

insects are arguably the toughest animals our world has

Amy Martin: 00:04:46

ever known, that they've made it through multiple mass

Amy Martin: 00:04:49

extinctions, major climatic changes and a total

Amy Martin: 00:04:53

rearrangement of the continents, and they're also just, well, Wil

Amy Martin: 00:04:59

Hershberger says it best.

Wil Hershberger: 00:05:01

Many of our singing insects are handsome, if

Wil Hershberger: 00:05:03

not downright beautiful. From the tiny trigs and ground

Wil Hershberger: 00:05:07

crickets through the meadow and conehead katydids to the true

Wil Hershberger: 00:05:11

and false katydids, there's an almost endless variety of

Wil Hershberger: 00:05:15

shapes, colors and sounds to explore.

Amy Martin: 00:05:18

That's Wil introducing people to the

Amy Martin: 00:05:20

website songsofinsects.com and I challenge you to visit this site

Amy Martin: 00:05:26

and not fall in love with at least one insect. It is chock

Amy Martin: 00:05:30

full of pictures, videos, information and sound recordings

Amy Martin: 00:05:34

of a huge array of six legged singers. There's the slow,

Amy Martin: 00:05:39

tinkling trig, the confused ground cricket, the scissor

Amy Martin: 00:05:46

grinder cicada and the slightly musical conehead, kind of a

Amy Martin: 00:05:55

passive aggressive name, but sorry, coneheads, I think it's

Amy Martin: 00:05:59

accurate. Insects make thousands of different kinds of sounds,

Amy Martin: 00:06:05

and they also have an impressive variety of ways to listen.

Amy Martin: 00:06:12

Dr. Natasha Mhatre: The fun thing about insects is that they

Amy Martin: 00:06:14

have evolved hearing at least 17 times independently, so they've

Amy Martin: 00:06:20

invented ears over and over and over again.

Amy Martin: 00:06:25

This is Dr Natasha Mhatre. She's the one who told

Amy Martin: 00:06:28

us about how spider webs can be ears in our last episode. She's

Amy Martin: 00:06:33

based at the University of Western Ontario, and she

Amy Martin: 00:06:36

researches invertebrate neurobiology. In other words,

Amy Martin: 00:06:41

she's an expert in bug brains and especially how insects and

Amy Martin: 00:06:45

spiders process sound. She says, insects grow ears in all sorts

Amy Martin: 00:06:51

of places on their bodies.

Amy Martin: 00:06:53

Dr. Natasha Mhatre: Grasshoppers have them on the abdomen, so in

Amy Martin: 00:06:56

one of the segments of their body. Crickets have them on

Amy Martin: 00:07:00

their forelegs, so they move the ears as they walk.

Amy Martin: 00:07:03

Cool!

Amy Martin: 00:07:04

Natasha says one kind of moth even grows an ear on its mouth.

Amy Martin: 00:07:09

So the thing it eats with is also the thing it hears with.

Amy Martin: 00:07:14

Dr. Natasha Mhatre: I would not want to be this moth because,

Amy Martin: 00:07:16

like it would sound awful.

Amy Martin: 00:07:19

Arthropods currently make up more than 80% of Earth's

Amy Martin: 00:07:23

animal species, on land and in the sea, and insects are the

Amy Martin: 00:07:27

largest group of animals in that category. All of which is to say

Amy Martin: 00:07:31

it would be impossible to do a full survey of all the sonic

Amy Martin: 00:07:35

wonders of the arthropod world. So I decided to focus on just

Amy Martin: 00:07:39

one especially creative specimen, the tree cricket. The

Amy Martin: 00:07:43

delicate green cousin of the much burlier field cricket.

Amy Martin: 00:07:47

Dr. Natasha Mhatre: They're actually quite slender. They

Amy Martin: 00:07:49

look like blades of grass. And the males have these like

Amy Martin: 00:07:53

lovely, beautiful glass, like wings. And when they sing, their

Amy Martin: 00:07:58

wings are flipped up and they're almost completely transparent.

Amy Martin: 00:08:01

They just look so pretty.

Amy Martin: 00:08:03

Is it fair to say that you have a special

Amy Martin: 00:08:05

relationship with tree crickets?

Amy Martin: 00:08:06

Dr. Natasha Mhatre: I have a special relationship with tree

Amy Martin: 00:08:08

crickets.

Amy Martin: 00:08:12

Tree crickets punch way, way above their weight

Amy Martin: 00:08:15

class in terms of making themselves heard. They are

Amy Martin: 00:08:19

really small and they can be really loud.

Amy Martin: 00:08:22

Dr. Natasha Mhatre: They're super cool. They live pretty

Amy Martin: 00:08:24

much everywhere. There's tree crickets in Australia, there's

Amy Martin: 00:08:27

three crickets all over Asia. North America, South America.

Amy Martin: 00:08:30

They're in Africa. I don't think there's any in the Antarctic,

Amy Martin: 00:08:33

but that's it. So they're everywhere this, you know, it's

Amy Martin: 00:08:36

lots of species, so you can probably find a tree cricket

Amy Martin: 00:08:39

somewhere close to you.

Amy Martin: 00:08:41

Natasha says it's a common misconception that they

Amy Martin: 00:08:44

make their sounds by rubbing their legs together, but tree

Amy Martin: 00:08:48

crickets actually sing with their wings. One wing has a row

Amy Martin: 00:08:55

of pegs on it called the file, and on the other there's a tiny

Amy Martin: 00:08:59

little lump called the plectrum. When the tree cricket rubs its

Amy Martin: 00:09:03

wings together, the plectrum runs down the file like a guitar

Amy Martin: 00:09:07

pick running down the strings. It's called stridulation, and

Amy Martin: 00:09:11

when I slow the recording way down, you can hear each

Amy Martin: 00:09:15

individual wing beat. Tree crickets are actually moving

Amy Martin: 00:09:21

their wings up to 100 times per second, turning the sound of

Amy Martin: 00:09:24

their wing beats into an acoustic blur, at least our

Amy Martin: 00:09:28

ears. There's quite a bit of variety in tree cricket song.

Amy Martin: 00:09:34

Some make sustained trills. Others like to lay down a

Amy Martin: 00:09:39

groove, but all of this high speed wing strumming is

Amy Martin: 00:09:44

essentially a love song. Males do it to attract females, and

Amy Martin: 00:09:49

the gals are choosy. They listen to the songs not only to locate

Amy Martin: 00:09:54

their suitors among the leaves, but also to assess them.

Amy Martin: 00:09:59

Consider the situation of two romantically inclined tree

Amy Martin: 00:10:03

crickets. Two almost weightless, little beings living in a

Amy Martin: 00:10:07

dangerous world. With predators all around ready to turn them

Amy Martin: 00:10:11

into a tasty meal, hiding is essential. Their bodies have

Amy Martin: 00:10:16

evolved to blend in among the stems and leaves, and they're

Amy Martin: 00:10:20

very good at holding very still, but that means tree crickets are

Amy Martin: 00:10:27

hidden from each other too, until the male starts to sing.

Amy Martin: 00:10:31

His song is an acoustic beacon cutting through the night,

Amy Martin: 00:10:35

broadcasting his location. Instead of a profile picture, he

Amy Martin: 00:10:39

has a profile song, and instead of swiping left or right, the

Amy Martin: 00:10:44

females, with two ears located on two different legs, listen to

Amy Martin: 00:10:48

the serenades and hop left or right, slowly working their way

Amy Martin: 00:10:53

toward the fellow of their choice.

Amy Martin: 00:10:55

Dr. Natasha Mhatre: You know the purity of the tone the animal

Amy Martin: 00:10:57

produces tells you something about the condition of the

Amy Martin: 00:11:00

wings. So is this an old animal? Is this a young animal? Are half

Amy Martin: 00:11:04

his teeth missing?

Amy Martin: 00:11:09

Wow. So we got like, a bunch of judgmental lady

Amy Martin: 00:11:12

crickets.

Amy Martin: 00:11:12

Dr. Natasha Mhatre: Totally. Well, they're like, if I'm gonna

Amy Martin: 00:11:15

spend the time walking up to you, wherever the hell you are

Amy Martin: 00:11:18

and finding you, you better be worth my while.

Amy Martin: 00:11:22

And I'm gonna tell that by the quality of your,

Amy Martin: 00:11:27

your plucking.

Amy Martin: 00:11:27

Dr. Natasha Mhatre: That plus just how long you go like

Amy Martin: 00:11:30

crickets that you know have a little bit of stamina do better.

Amy Martin: 00:11:35

Yeah.

Amy Martin: 00:11:36

Evolution is cruel.

Amy Martin: 00:11:42

So for the males, it's all about getting heard, and sometimes to

Amy Martin: 00:11:47

increase their chances, they actually build their own

Amy Martin: 00:11:50

cricket-sized megaphones using all local recyclable materials

Amy Martin: 00:11:54

to boot. They're called baffles. And male tree crickets make them

Amy Martin: 00:11:59

out of leaves. They chew holes into them and stick their heads

Amy Martin: 00:12:02

through, and when they stratulate Their wings, the leaf

Amy Martin: 00:12:05

turns up the volume on their songs.

Amy Martin: 00:12:08

Dr. Natasha Mhatre: Think of making your wings artificially

Amy Martin: 00:12:10

bigger.

Amy Martin: 00:12:11

Natasha ran experiments to test the

Amy Martin: 00:12:13

cricket's baffle-making abilities, and she discovered

Amy Martin: 00:12:16

that they're almost freakishly good at it. Even before they

Amy Martin: 00:12:19

start the building process, they're somehow calculating

Amy Martin: 00:12:23

which leaves to use as raw materials.

Amy Martin: 00:12:25

Dr. Natasha Mhatre: If you give them a small leaf, they probably

Amy Martin: 00:12:25

won't make a baffle. If you give them a nice, big one that really

Amy Martin: 00:12:30

gives them a lot of benefit, they will make it. They don't

Amy Martin: 00:12:35

even need to sing on the leaf to know if it's the big one. They

Amy Martin: 00:12:38

seem to have some way of figuring it out in the darkness,

Amy Martin: 00:12:41

they ignore the small leaf. They go straight for the big one.

Amy Martin: 00:12:45

And once they've chosen the leaf they want, they

Amy Martin: 00:12:48

demonstrate an incredible level of skill.

Amy Martin: 00:12:51

Dr. Natasha Mhatre: They don't baffle kind of willy nilly. They

Amy Martin: 00:12:54

try and go to the center of the leaf, which is the best

Amy Martin: 00:12:57

position, make this perfectly sized hole there. They'll stick

Amy Martin: 00:13:00

their wings through start singing, oh, that hole isn't

Amy Martin: 00:13:04

just right. They might go trim the edges a little bit and make

Amy Martin: 00:13:07

it the right size, and then they'll sing from it.

Amy Martin: 00:13:10

If I wanted to become an acoustical engineer, I

Amy Martin: 00:13:13

would likely study baffles and how they work, and it would

Amy Martin: 00:13:16

involve math and physics. But here are these very small

Amy Martin: 00:13:20

animals with tiny brains who figured it out. Natasha says

Amy Martin: 00:13:25

these skills are innate to some tree crickets. It's not a

Amy Martin: 00:13:28

learned behavior it's genetically programmed, but some

Amy Martin: 00:13:32

of them do have behaviors that look like learning, like a

Amy Martin: 00:13:36

craftsman, critiquing his work and making improvements as he

Amy Martin: 00:13:40

goes.

Amy Martin: 00:13:41

Dr. Natasha Mhatre: This one guy didn't get to the center, and

Amy Martin: 00:13:44

he's like, this is no good. Then he went and chewed the second

Amy Martin: 00:13:47

hole and went straight for that.

Amy Martin: 00:13:49

Amazing. That just seems like fairly complex

Amy Martin: 00:13:52

problem solving. I couldn't do that.

Amy Martin: 00:13:56

And the work doesn't end there. If a male tree cricket manages

Amy Martin: 00:14:01

to attract a female, then he has to feed her. He produces a

Amy Martin: 00:14:05

secretion from a gland on his back, which apparently tastes

Amy Martin: 00:14:09

really good to the ladies. Scientists call it the nuptial

Amy Martin: 00:14:13

gift, but that seems pretty euphemistic to me. I think we

Amy Martin: 00:14:18

should call it a honey pot.

Amy Martin: 00:14:20

Dr. Natasha Mhatre: The female climbs on top of the male. She

Amy Martin: 00:14:23

eats from that gland while he mates with her.

Amy Martin: 00:14:27

She is dining while mating.

Amy Martin: 00:14:29

Dr. Natasha Mhatre: Yep, and it's like, you know, how tasty

Amy Martin: 00:14:31

can I make this? The longer she feeds, the more sperm that get

Amy Martin: 00:14:35

transferred into her, so the higher likelihood of him getting

Amy Martin: 00:14:39

babies in the next generation. So there's a lot of investment

Amy Martin: 00:14:43

in whatever that nuptial feeding is.

Amy Martin: 00:14:46

And the males are the true multi-taskers here,

Amy Martin: 00:14:49

because they continue to sing while all of this is going on.

Amy Martin: 00:14:53

Natasha says she doesn't really know why.

Amy Martin: 00:14:56

Dr. Natasha Mhatre: I guess they're like, let it carry on.

Amy Martin: 00:14:58

Maybe then the sound will continue convincing the female

Amy Martin: 00:15:01

to stay. I don't know for sure.

Amy Martin: 00:15:02

Huh. Yeah, it just almost seems like logistically

Amy Martin: 00:15:06

difficult to do so many things at once. Serve a meal, have sex

Amy Martin: 00:15:06

Anything to keep her there.

Amy Martin: 00:15:10

and keep singing.

Amy Martin: 00:15:18

After talking with Natasha, I realized I was hearing tree

Amy Martin: 00:15:21

crickets all the time without knowing what they were, so I

Amy Martin: 00:15:25

decided to track one down on a September evening in a little

Amy Martin: 00:15:29

nature preserve not far from my home in Missoula, Montana.

Amy Martin: 00:15:34

I'm tiptoeing through this field.

Amy Martin: 00:15:38

With my microphone out and my headphones on, I let my ears

Amy Martin: 00:15:42

guide me through the tall grass.

Amy Martin: 00:15:45

Definitely a case of the whole the elusive, whatever you are.

Amy Martin: 00:15:51

I take a quiet step...

Amy Martin: 00:15:55

That is a squirrel.

Amy Martin: 00:15:57

And then another...

Amy Martin: 00:16:00

Okay, maybe you're in here somewhere.

Amy Martin: 00:16:03

And finally, I see it. It's a tiny wisp of a thing with

Amy Martin: 00:16:10

delicate lacy wings clinging to a blade of grass. It is, indeed

Amy Martin: 00:16:16

a tree cricket, and for the moment, at least, he's alone,

Amy Martin: 00:16:21

but there's probably a female tree cricket nearby, listening

Amy Martin: 00:16:25

like I am. Maybe she's pointing a leg at him in order to hear

Amy Martin: 00:16:29

him better, just like I'm doing with the mic.

Amy Martin: 00:16:35

It's very light green. I've heard it all my life here in

Amy Martin: 00:16:40

Montana, and never stopped and tried to figure out what it was.

Amy Martin: 00:16:47

It's beautiful.

Amy Martin: 00:16:48

As I sit here in the grass taking in the song, I know that

Amy Martin: 00:16:59

I'm a listener within a community of listeners. There

Amy Martin: 00:17:03

are other people walking around. I can hear an owl across the

Amy Martin: 00:17:06

clearing. But what about the branches of the Ponderosa pine

Amy Martin: 00:17:11

tree above me? Or the milkweed plants nearby? Or the blade of

Amy Martin: 00:17:18

grass itself that the tree cricket is singing on? They've

Amy Martin: 00:17:22

all been bathed in this song all summer long. But of course,

Amy Martin: 00:17:27

they're plants. They can't hear. They're not listening, right?

Amy Martin: 00:17:36

We'll have more after this short break.

Matt Herlihy: 00:17:39

Hi, my name is Matt Herlihy, and I've been a

Matt Herlihy: 00:17:59

Threshold listener and donor since season one came out in

Matt Herlihy: 00:18:02

2017. I was also one of the first volunteer board members of

Matt Herlihy: 00:18:05

the nonprofit organization that makes Threshold. Over the past

Matt Herlihy: 00:18:09

seven plus years, I've had this unique first hand look at just

Matt Herlihy: 00:18:12

how much work it takes to make this kind of show. I mean, the

Matt Herlihy: 00:18:15

the time, the dedication, the determination that's required to

Matt Herlihy: 00:18:18

tell these, these in depth stories that really make people

Matt Herlihy: 00:18:21

think and feel, and give people a sense of what it's like to

Matt Herlihy: 00:18:24

really go to places where the stories are happening, to talk

Matt Herlihy: 00:18:26

to the people who are part of them. It creates this rich,

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immersive listening experience, And I'm telling you, that kind

Matt Herlihy: 00:18:32

of reporting, this whole kind of show, is not easy to make. It's

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also not easy to fund. Talk about slow, in depth, thorough.

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These are not often part of the existing models for making a

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podcast, so it's up to people like us to really make sure

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Threshold can get made. I believe what Threshold is doing

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really matters, and if you do too, help them keep doing it.

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Threshold's Year End fundraising campaign is happening right now

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through December 31 and each gift will be doubled through

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NewsMatch. So if you give $25 they'll receive 50. You can make

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your one time or monthly donation online at

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thresholdpodcast.org just click the donate button and give what

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you can. Thank you.

Dallas Taylor: 00:19:17

I'm Dallas Taylor, host of 20,000 Hertz, a

Dallas Taylor: 00:19:21

podcast that reveals the untold stories behind the sounds of our

Dallas Taylor: 00:19:24

world. We've uncovered the incredible intelligence of

Dallas Taylor: 00:19:28

talking parrots.

Unknown: 00:19:29

Basically, bird brain was a pejorative term, and here

Unknown: 00:19:33

I had this bird that was doing the same types of tasks the

Unknown: 00:19:37

primates.

Dallas Taylor: 00:19:38

We've investigated the bonding power

Dallas Taylor: 00:19:40

of music.

Unknown: 00:19:41

There's an intimacy there in communicating through

Unknown: 00:19:44

the medium of music that can be really a powerful force for

Unknown: 00:19:48

bringing people together.

Dallas Taylor: 00:19:50

We've explored the subtle nuances of the human

Dallas Taylor: 00:19:52

voice.

Unknown: 00:19:53

We have to remember that humans, over many hundreds

Unknown: 00:19:56

of thousands of years of evolution, have become extremely

Unknown: 00:19:59

attuned to the sounds of each other's voices.

Dallas Taylor: 00:20:01

And we've revealed why a famous composer

Dallas Taylor: 00:20:03

wrote a piece made entirely of silence.

Unknown: 00:20:06

I think that's a really potentially quite useful and

Unknown: 00:20:09

quite profound experience to have.

Dallas Taylor: 00:20:11

Subscribe to 20,000 Hertz right here in your

Dallas Taylor: 00:20:14

podcast player. I'll meet you there.

Amy Martin: 00:20:18

Hi Threshold listeners. Do you ever find

Amy Martin: 00:20:20

yourself wondering what businesses are doing and what

Amy Martin: 00:20:23

more they should do to confront climate change? Then you should

Amy Martin: 00:20:26

check out Climate Rising, the award winning podcast from

Amy Martin: 00:20:30

Harvard Business School. Climate Rising gives you a behind the

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scenes look at how top business leaders are taking on the

Amy Martin: 00:20:37

challenge of climate change. The show covers cutting edge

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solutions, from leveraging AI and carbon markets to sharing

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stories that inspire climate action. Recent episodes feature

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insightful conversations with leaders like Netflix's first

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sustainability officer, Emma Stewart, who discusses how the

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global entertainment giant uses its platform to promote climate

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awareness. You'll also hear from CNN chief climate correspondent,

Amy Martin: 00:21:04

Bill Weir, about the importance of integrating climate change

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into news coverage. Each episode dives deep into the challenges

Amy Martin: 00:21:12

and opportunities that climate change presents to entrepreneurs

Amy Martin: 00:21:16

and innovators. Listen to Climate Rising every other

Amy Martin: 00:21:19

Wednesday on Apple podcasts, Spotify, or wherever you get

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your podcasts.

Amy Martin: 00:21:32

Welcome back to Threshold, I'm Amy Martin, and let's return for

Amy Martin: 00:21:35

a minute to that time before there were any plants on land.

Amy Martin: 00:21:41

No grasses, no flowers, no trees. That's how our Earth has

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been for most of its history, even long after plants began to

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grow in the oceans, the world above the seas continued to be

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dominated by rocks and dust. Plants and insects ventured into

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that forbidding, lifeless terrain and transformed it

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together. They've co-evolved for hundreds of millions of years,

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and they have an endlessly complex and intimate set of

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bonds. Like any close connections, their relationships

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can run the whole gamut from quiet coexistence to mutual

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support to intense conflict. Plants and insects depend on

Amy Martin: 00:22:32

each other, and sometimes they try to kill each other.

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Dr. Heidi Appel: Well, for most of my career, I've been studying

Amy Martin: 00:22:40

how plants defend themselves against insects, and they do

Amy Martin: 00:22:45

that through chemistry.

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Dr Heidi Appel is a biologist currently at the

Amy Martin: 00:22:49

University of Houston, and she specializes in chemical ecology.

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Dr. Heidi Appel: Plants actually evolve to ward off their own

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pests, including microorganisms that cause disease.

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When plants get attacked by insects, they can't

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get up and run away. What they can do is make and release nasty

Amy Martin: 00:23:09

tasting chemicals or even poison. And many plants are very

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sophisticated chemists. They can produce different compounds to

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target specific kinds of invaders, and sometimes they can

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even differentiate between intentional and accidental

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damage. For example, when a moth eats a leaf, a plant might send

Amy Martin: 00:23:29

out a little chemical warning shot, hoping to shoo it away.

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But when a falling twig rips a hole in a leaf, that same plant

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ignores it. So this is Heidi's world- plants, insects and

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chemicals.

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Dr. Heidi Appel: So sound was not on my radar at all until I

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moved to the University of Missouri and met Rex Cocroft

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after a biology seminar.

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Dr Rex Cocroft is an expert in insect communication.

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We met him in our last episode, and for decades, he's been

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researching how some insects send their sounds out through

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the bodies of plants. So Heidi and Rex both happen to go to

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this seminar and start chatting. This was in 2007.

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Dr. Heidi Appel: And I, you know, I explained what I did,

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and Rex said, Well, I study the way that insects use sound

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transmitted through plants to communicate with each other.

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So here's Heidi describing her research on how

Amy Martin: 00:24:30

plants respond to insects, and here's Rex describing how some

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insects use plants to send messages to each other.

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Dr. Heidi Appel: He paused and I paused, and we kind of looked at

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each other, complete strangers, you know, until now.

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They were both stopped in their tracks with the

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same thought.

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Dr. Heidi Appel: Oh, you don't suppose, do you that the plant

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can use vibration information for its own purposes?

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Dr. Rex Cocroft: That's when I think, we both began to wonder

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about from our own perspective, like, well, could any of this

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information be relevant to the plant, and could the plant be

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using any of it?

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Dr. Heidi Appel: That was the aha moment.

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It seemed like a pretty radical idea, kooky even,

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because if the plant was somehow using the vibrations caused by

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insects, that would mean plants could kind of hear, maybe not

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the way we hear, but still detect vibrations, receive

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acoustic information, maybe even from the animal world, and do

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something with it.

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that's really what kicked off this study, and we've been

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collaborating closely ever since.

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It was already known at that point that plants responded to

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sounds made by humans.

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Dr. Heidi Appel: Plants will respond to single tones or to

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music in all kinds of ways.

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Dr. Rex Cocroft: If you play a tone, just a pure tone, like you

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could increase crop yields. There's a whole range of plant

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traits that will be altered.

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Dr. Heidi Appel: The real mystery for Rex and me, because

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we were trained as ecologists, was why would plants have that

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Dr. Rex Cocroft: And that's where our work came in, is that

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ability?

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Playing music or electronic tones to plants is

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we said, well, what's an ecologically relevant acoustic

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very human centric. It's asking, how do plants respond to these

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stimulus for a plant and what would be a relevant response?

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sounds we're making? It's very different to ask a plant or an

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animal or another person, what, if any, sounds are important to you?

Unknown: 00:26:35

So that became really the focus of our work, relevant

Unknown: 00:26:52

sounds and relevant responses to plants.

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To explore this, Heidi and Rex needed to identify

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a distinctive vibration produced by an activity that mattered to

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plants, and this sound quickly came to mind. This is a

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caterpillar chewing on a leaf. Rex was very familiar with these

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sounds because they'd been driving him bananas for a long

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time. He was constantly having to remove very hungry

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caterpillars like this one from his plants in order to get good

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recordings of tree hoppers. So he knew this was a conspicuous

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sound produced when an insect was doing something very

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biologically relevant to the plant- eating it.

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Dr. Rex Cocroft: If there was a caterpillar on the plant feeding

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on a leaf, then that's mostly what you're going to hear.

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And Heidi knew about the chemicals plants produce

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when this is happening.

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Dr. Heidi Appel: When a caterpillar bites at plant, it

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gives lots of signals that damage has occurred. So tissue

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is damaged, things leak out of cells that triggers defense

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responses, and then caterpillars actually drool some, they have

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some oral secretions when they feed, and that chemistry also

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influences how the plant responds.

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By combining their expertise, Heidi and Rex could

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try to answer a novel question, would a plant respond to the

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vibrations of a chomping caterpillar, even if there was

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no actual caterpillar present? If so, that would mean that the

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plant was essentially listening to or feeling for the

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caterpillar and responding.

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Dr. Rex Cocroft: To think of the plant as a kind of active

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listener. I never thought about that.

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They got to work designing an experiment to find

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out. Rex was in charge of vibes, Heidi was in charge of

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chemicals. Step one, was to figure out how to vibrate

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individual leaves of a plant in a very caterpillary way, to give

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the plant the experience of being eaten, but without any

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chemicals being transmitted.

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Dr. Heidi Appel: We want to just separate the effect of the

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vibrations.

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So Rex essentially built a little munching

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caterpillar mimicry machine, minus the drool. They attached

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it to some leaves, and Heidi measured the chemical responses.

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Dr. Heidi Appel: And we found that the ones that had received

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the feeding vibrations made more of the chemical defenses than

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the ones that hadn't received the feeding vibrations.

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Uh huh.

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So it wasn't just the drool or some other element of

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caterpillar chemistry at play. The plant did, in fact, seemed

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to be responding to the vibrations.

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Dr. Heidi Appel: And that surprised us. We thought, oh,

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maybe it's a fluke.

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Ever the careful scientists, Heidi and Rex

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interrogated their results.

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Dr. Rex Cocroft: Well, it was interesting. I in no way

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believed it at that point.

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They didn't believe it yet, because they didn't know

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if the plant was alerted by the vibrations of chewing in

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particular.

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Dr. Heidi Appel: Maybe the plants just respond to anything,

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you know. Maybe this isn't a significant response, because

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they'll respond to all kinds of things with their environment.

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So they planned a second experiment. This time

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they exposed the plants to three different vibrations, all of

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them naturally occurring in the environment. The munching

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caterpillar, a light wind and a leaf hopper call. These little

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insects are related to the tree hoppers we met in our last

Amy Martin: 00:30:35

episode. The vibrations they produce are in a very similar

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frequency to the vibrations made by dining caterpillars, but

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these are mating calls. They don't signal any danger to the

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plant.

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Dr. Heidi Appel: So we thought that would be a pretty good test

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to see how specific this plant response to feeding vibrations

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is.

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So we've got wind, tree hopper calls and

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caterpillar chomps. Three kinds of vibrations with similar

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frequencies, but only one of them signals a threat. So, if

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the plants produce more defensive chemicals in response

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to the caterpillar, it would indicate that they're listening

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or feeling for those vibrations in particular and responding to

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them. Rex and Heidi, vibrated the leaves again, measured the

Amy Martin: 00:31:23

chemical responses again, and waited for the results to come

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in. To help eliminate bias, they put their measurements into a

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sort of code.

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Dr. Heidi Appel: We don't identify the samples as coming

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from one treatment or another, so they come out as a bunch of

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numbers.

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Those numbers then go into a spreadsheet that

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decodes the data.

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Dr. Heidi Appel: So you're sitting at a computer, you've

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been sitting for four hours getting all the data aligned and

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in the system.

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And then finally, the results were revealed. The

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plants that had received the caterpillar vibrations had

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produced more defensive chemicals than the others.

Amy Martin: 00:32:04

Dr. Heidi Appel: I remember sitting there screaming, there's

Amy Martin: 00:32:09

a difference here and not here! And I think I might have even

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gotten up and done a happy dance. And of course, right away

Amy Martin: 00:32:16

I'm texting Rex.

Amy Martin: 00:32:19

The plants were listening out for the vibrations

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that mattered the most.

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Dr. Heidi Appel: So yeah, it was very, a very exciting moment.

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And, you know, I I feel lucky if I had, I've had one of those

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this exciting in my whole scientific career. And if I

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never have another one, I'll die happy.

Amy Martin: 00:32:42

Because this really hadn't, no one knew this before.

Amy Martin: 00:32:46

You added something new to our scientific knowledge of plants.

Amy Martin: 00:32:51

Dr. Heidi Appel: Yes, we did. Because even though people knew

Amy Martin: 00:32:54

that plants could respond to these other synthetic tones or

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music, right, the fact that he could discriminate between a

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biologically relevant sound and one that wasn't, was a real big

Amy Martin: 00:33:07

advance in our understanding.

Amy Martin: 00:33:13

It's not very often that you get to talk to people

Amy Martin: 00:33:15

who've made major scientific breakthroughs like this, and as

Amy Martin: 00:33:19

a scientist, it's not very often that you get to be one of those

Amy Martin: 00:33:23

people.

Amy Martin: 00:33:24

Do you feel a little bit like Galileo looking through the

Amy Martin: 00:33:27

telescope for the first time of like, oh my gosh!

Amy Martin: 00:33:32

Dr. Heidi Appel: It does cause me to look at the world very

Amy Martin: 00:33:34

differently, but I don't think we're going to have the impact

Amy Martin: 00:33:36

that Galileo.

Amy Martin: 00:33:39

Maybe not, but Rex and Heidi's discovery did make a

Amy Martin: 00:33:43

big splash. It was covered in newspapers around the world, and

Amy Martin: 00:33:47

they got interviewed countless times. It was all pretty

Amy Martin: 00:33:51

shocking to them. Rex says when they started down this path, he

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was very skeptical that they would find anything of interest.

Amy Martin: 00:33:58

The idea of plants being able to engage in a sort of dialog with

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animals, just seemed too out there.

Amy Martin: 00:34:05

Dr. Rex Cocroft: But it now has become firmly established in my

Amy Martin: 00:34:09

mind that if you're studying communication through plants,

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that one of the potential receivers of these signals is

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the plant, and that we need to think about that.

Amy Martin: 00:34:19

Now that we know that plants can detect and

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respond to biologically relevant sounds like munching

Amy Martin: 00:34:25

caterpillars, it seems kind of surprising that it took us this

Amy Martin: 00:34:28

long to figure it out, and indeed, from the perspective of

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many indigenous people, research like this is not so much a

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discovery of new information as it is an incorporation of wisdom

Amy Martin: 00:34:40

that's been there all along. But by testing this question inside

Amy Martin: 00:34:45

the framework of Western science, Rex and Heidi helped to

Amy Martin: 00:34:49

bridge that gap between different ways of knowing.

Amy Martin: 00:34:52

They've provided hard evidence for plant listening, a whole

Amy Martin: 00:34:56

layer of relationship really happening all around us every

Amy Martin: 00:35:00

day. Scientists knew that plants and animals compete and

Amy Martin: 00:35:04

cooperate, now they know that they also converse. They've gone

Amy Martin: 00:35:10

from assuming sound was irrelevant to plants to

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understanding that plants are actually super receivers of

Amy Martin: 00:35:17

sounds and vibrations.

Amy Martin: 00:35:18

Dr. Rex Cocroft: The soundscape, or the vibroscape, if you will,

Amy Martin: 00:35:20

of a living plant is one of the most complex soundscapes that

Amy Martin: 00:35:24

there is.

Amy Martin: 00:35:27

Leaves capture the airborne sound environment.

Amy Martin: 00:35:29

Sounds in the soil can move up through the roots.

Amy Martin: 00:35:33

Dr. Rex Cocroft: And then you have all of the incredible

Amy Martin: 00:35:37

sounds or vibrations created by insects and other animals that

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are in contact with the plant.

Amy Martin: 00:35:42

Understanding this, the question shifts from why

Amy Martin: 00:35:46

would plants respond to sound to why wouldn't they?

Amy Martin: 00:35:52

I'm curious if you feel more closely connected to plants

Amy Martin: 00:35:57

because of this, because you've been listening to insects for

Amy Martin: 00:36:00

decades now, and here, turns out plants are also listening. Does

Amy Martin: 00:36:04

it give you more of a sense of kinship with them?

Amy Martin: 00:36:07

Dr. Rex Cocroft: I think it does. I would say that it does.

Amy Martin: 00:36:10

There's some physical information out there that I'm

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really interested in, that the plant also has a stake in. So

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yes, it does provide a perhaps a little bit of a fellow feeling.

Amy Martin: 00:36:22

If you hear some wariness in Rex's voice, I think

Amy Martin: 00:36:25

it's a reflection of the fact that people can get really

Amy Martin: 00:36:28

polarized around plants. On one side are hardcore mystics who

Amy Martin: 00:36:33

insist on things like plants can read minds and predict the

Amy Martin: 00:36:36

future. On the other are militant guardians of the ivory

Amy Martin: 00:36:41

tower who seem eager to attack anyone who proposes a slightly

Amy Martin: 00:36:46

out of the box research idea. But there are many people who

Amy Martin: 00:36:50

are working in the exciting and often uncomfortable territory

Amy Martin: 00:36:54

between these two fairly rigid camps, people like Heidi, Rex

Amy Martin: 00:36:59

and some scientists we'll meet in our next episode too, who are

Amy Martin: 00:37:03

asking brave questions and doing solid evidence based work to try

Amy Martin: 00:37:08

to answer them.

Amy Martin: 00:37:09

Dr. Rex Cocroft: I would say, in some ways, plants do almost

Amy Martin: 00:37:11

everything that animals do. They just do it really differently.

Amy Martin: 00:37:16

We're walking around in the world that plants made.

Amy Martin: 00:37:20

Every creature on earth, from Dolly Parton on down, depends on

Amy Martin: 00:37:24

them for survival. Intellectually, I know this. I

Amy Martin: 00:37:29

know my survival rests on all these other living things that I

Amy Martin: 00:37:33

often ignore, but the work of these scientists helps me feel

Amy Martin: 00:37:38

it.

Amy Martin: 00:37:40

Dr. Heidi Appel: When we can identify with other living

Amy Martin: 00:37:43

organisms, it creates an empathy in us that I think will allow us

Amy Martin: 00:37:48

to be better stewards of the planet.

Amy Martin: 00:37:51

It feels like it makes plants less other.

Amy Martin: 00:37:55

Dr. Heidi Appel: It's this common sense of being alive and

Amy Martin: 00:37:59

being interconnected, which I think is really important to our

Amy Martin: 00:38:04

development as humans.

Amy Martin: 00:38:09

Maybe someday we'll learn that plants do have

Amy Martin: 00:38:12

supernatural powers, but in the meantime, just the natural seems

Amy Martin: 00:38:17

wondrous enough.

Amy Martin: 00:38:34

This episode of Threshold was written, reported and produced

Amy Martin: 00:38:38

by me, Amy Martin, with help from Erika Janik and Sam Moore.

Amy Martin: 00:38:43

Music by Todd Sickafoose. Post production by Alan Douches. Fact

Amy Martin: 00:38:47

checking by Sam Moore. Special thanks to Natasha Mhatre, Rex

Amy Martin: 00:38:51

Cocroft and Heidi Appel for some of the insect sounds you heard

Amy Martin: 00:38:56

in this episode, and to Chris Peiffer at WGTE Public Media.

Amy Martin: 00:39:00

Threshold is made by Auricle Productions, a non profit

Amy Martin: 00:39:04

organization powered by listener donations. Deneen Weiske is our

Amy Martin: 00:39:09

executive director. You can find out more about our show at thresholdpodcast.org.