December 17, 2024 • 37 mins
Insects invented song. They’ve developed a multitude of ways to listen. But insects couldn’t have evolved these complex skills without plants. In this episode, we explore the interconnected acoustic lives of insects and plants.
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Episode Transcript
Available transcripts are automatically generated. Complete accuracy is not guaranteed.
Amy Martin (00:00):
We're in eastern Tennessee half a billion years
(00:03):
ago. The land we now call theSmoky Mountains is almost
totally covered by a shallowsea, and life on Earth is still
mostly confined to the oceans,until a tiny moss does something
remarkable. It finds a footholdon some rocks and stays there.
(00:29):
It's an early pioneer into thebarren world above the waves, an
adventurer that helps to turnthe terrestrial world green. Now
fast forward hundreds ofmillions of years to 1946. Just
down river from the very spotwhere that ancient moss lived
(00:53):
and died, another Trailblazer isborn.
Dolly Parton (00:56):
Sitting on the front porch on a summer
afternoon.
Amy Martin (01:02):
Dolly Parton.
Dolly Parton (01:03):
In a straight back chair on two legs, leaned
against the wall.
Amy Martin (01:10):
Raised in a one room cabin with 11 siblings, Dolly
went on to write thousands ofsongs, many of them full of
references to the wild thingsshe grew up with. This one
called "My Tennessee MountainHome" recounts a childhood
filled with butterflies, birds,wildflowers and crickets.
Dolly Parton (01:34):
In my Tennessee mountain home, crickets sing in
the fields nearby.
Amy Martin (01:45):
So when a geologist unearthed that ancient moss near
Dolly's home and learned that itmight be one of the oldest
fossilized land plants everdiscovered, he named it
Dollyphyton boucotti in herhonor. A moss and a musician, a
plant and an animal. Thisconnection between flora and
(02:09):
fauna is fundamental to thesoundscape of our planet and the
flourishing of life overall.Because as plants began to
emerge out of the sea, someadventurous animals followed
suit. They were probablyscorpion-like creatures.
Arthropods, related to ourmodern insects and spiders, and
(02:31):
they were the very first animalsto scuttle across the untouched
beaches of the terrestrialworld. This new realm must have
been shockingly bright and dryfor the plants and the animals,
but finding no other life, theywent forth and multiplied and
(02:51):
multiplied and multiplied. Afterthe mosses and lichens came
ferns and trees, and about 150million years ago, came the
miracle of flowers, painting theworld in color and pollinated by
beetles, moths and other wingedthings. And as the world got
(03:12):
greener, it got louder. Cicadascalled from the branches,
crickets made choruses in theleaves. Insects invented song.
They laid down the very firstnotes of what would later become
a symphony of terrestrial sound.But they couldn't have done it
alone. Without plants, therewould be no animals, no songs at
(03:36):
all. So without Dollyphyton,there might never have been a
Dolly Parton. Welcome toThreshold, I'm Amy Martin, and
in this episode, we're going toexplore the intertwined acoustic
lives of plants and insects.
(04:20):
So I want to start by naming thedung beetle in the room here.
Both plants and insects arethings that people often ignore.
We just take it for granted thatplants spend their lives giving
us breathable air, stabilizingour climate and providing the
basis for every bite of food weconsume, and we forget that
(04:42):
insects are arguably thetoughest animals our world has
ever known, that they've made itthrough multiple mass
extinctions, major climaticchanges and a total
rearrangement of the continents,and they're also just, well, Wil
Hershberger says it best.
Wil Hershberger (05:01):
Many of our singing insects are handsome, if
not downright beautiful. Fromthe tiny trigs and ground
crickets through the meadow andconehead katydids to the true
and false katydids, there's analmost endless variety of
shapes, colors and sounds toexplore.
Amy Martin (05:18):
That's Wil introducing people to the
website songsofinsects.com and Ichallenge you to visit this site
and not fall in love with atleast one insect. It is chock
full of pictures, videos,information and sound recordings
of a huge array of six leggedsingers. There's the slow,
(05:39):
tinkling trig, the confusedground cricket, the scissor
grinder cicada and the slightlymusical conehead, kind of a
passive aggressive name, butsorry, coneheads, I think it's
(05:59):
accurate. Insects make thousandsof different kinds of sounds,
and they also have an impressivevariety of ways to listen.
Dr. Natasha Mhatre (06:12):
The fun thing about insects is that they
have evolved hearing at least 17times independently, so they've
invented ears over and over andover again.
Amy Martin (06:25):
This is Dr Natasha Mhatre. She's the one who told
us about how spider webs can beears in our last episode. She's
based at the University ofWestern Ontario, and she
researches invertebrateneurobiology. In other words,
she's an expert in bug brainsand especially how insects and
(06:45):
spiders process sound. She says,insects grow ears in all sorts
of places on their bodies.
Dr. Natasha Mhatre (06:53):
Grasshoppers have them on the abdomen, so in
one of the segments of theirbody. Crickets have them on
their forelegs, so they move theears as they walk.
Amy Martin (07:03):
Cool!
Natasha says one kind of motheven grows an ear on its mouth.
So the thing it eats with isalso the thing it hears with.
Dr. Natasha Mhatre (07:14):
I would not want to be this moth because,
like it would sound awful.
Amy Martin (07:19):
Arthropods currently make up more than 80% of Earth's
animal species, on land and inthe sea, and insects are the
largest group of animals in thatcategory. All of which is to say
it would be impossible to do afull survey of all the sonic
wonders of the arthropod world.So I decided to focus on just
one especially creativespecimen, the tree cricket. The
(07:43):
delicate green cousin of themuch burlier field cricket.
Dr. Natasha Mhatre (07:47):
They're actually quite slender. They
look like blades of grass. Andthe males have these like
lovely, beautiful glass, likewings. And when they sing, their
wings are flipped up and they'realmost completely transparent.
They just look so pretty.
Amy Martin (08:03):
Is it fair to say that you have a special
relationship with tree crickets?
Dr. Natasha Mhatre (08:06):
I have a special relationship with tree
crickets.
Amy Martin (08:12):
Tree crickets punch way, way above their weight
class in terms of makingthemselves heard. They are
really small and they can bereally loud.
Dr. Natasha Mhatre (08:22):
They're super cool. They live pretty
much everywhere. There's treecrickets in Australia, there's
three crickets all over Asia.North America, South America.
They're in Africa. I don't thinkthere's any in the Antarctic,
but that's it. So they'reeverywhere this, you know, it's
lots of species, so you canprobably find a tree cricket
somewhere close to you.
Amy Martin (08:41):
Natasha says it's a common misconception that they
make their sounds by rubbingtheir legs together, but tree
crickets actually sing withtheir wings. One wing has a row
of pegs on it called the file,and on the other there's a tiny
little lump called the plectrum.When the tree cricket rubs its
(09:03):
wings together, the plectrumruns down the file like a guitar
pick running down the strings.It's called stridulation, and
when I slow the recording waydown, you can hear each
individual wing beat. Treecrickets are actually moving
their wings up to 100 times persecond, turning the sound of
(09:24):
their wing beats into anacoustic blur, at least our
ears. There's quite a bit ofvariety in tree cricket song.
Some make sustained trills.Others like to lay down a
groove, but all of this highspeed wing strumming is
essentially a love song. Malesdo it to attract females, and
(09:49):
the gals are choosy. They listento the songs not only to locate
their suitors among the leaves,but also to assess them.
Consider the situation of tworomantically inclined tree
crickets. Two almost weightless,little beings living in a
dangerous world. With predatorsall around ready to turn them
(10:11):
into a tasty meal, hiding isessential. Their bodies have
evolved to blend in among thestems and leaves, and they're
very good at holding very still,but that means tree crickets are
hidden from each other too,until the male starts to sing.
His song is an acoustic beaconcutting through the night,
(10:35):
broadcasting his location.Instead of a profile picture, he
has a profile song, and insteadof swiping left or right, the
females, with two ears locatedon two different legs, listen to
the serenades and hop left orright, slowly working their way
toward the fellow of theirchoice.
Dr. Natasha Mhatre (10:55):
You know the purity of the tone the animal
produces tells you somethingabout the condition of the
wings. So is this an old animal?Is this a young animal? Are half
his teeth missing?
Amy Martin (11:09):
Wow. So we got like, a bunch of judgmental lady
crickets.
Dr. Natasha Mhatre (11:12):
Totally. Well, they're like, if I'm gonna
spend the time walking up toyou, wherever the hell you are
and finding you, you better beworth my while.
Amy Martin (11:22):
And I'm gonna tell that by the quality of your,
your plucking.
Dr. Natasha Mhatre (11:27):
That plus just how long you go like
crickets that you know have alittle bit of stamina do better.
Yeah.
Amy Martin (11:36):
Evolution is cruel.
So for the males, it's all aboutgetting heard, and sometimes to
increase their chances, theyactually build their own
cricket-sized megaphones usingall local recyclable materials
to boot. They're called baffles.And male tree crickets make them
(11:59):
out of leaves. They chew holesinto them and stick their heads
through, and when theystratulate Their wings, the leaf
turns up the volume on theirsongs.
Dr. Natasha Mhatre (12:08):
Think of making your wings artificially
bigger.
Amy Martin (12:11):
Natasha ran experiments to test the
cricket's baffle-makingabilities, and she discovered
that they're almost freakishlygood at it. Even before they
start the building process,they're somehow calculating
which leaves to use as rawmaterials.
Dr. Natasha Mhatre (12:25):
If you give them a small leaf, they probably
won't make a baffle. If you givethem a nice, big one that really
gives them a lot of benefit,they will make it. They don't
even need to sing on the leaf toknow if it's the big one. They
seem to have some way offiguring it out in the darkness,
they ignore the small leaf. Theygo straight for the big one.
Amy Martin (12:45):
And once they've chosen the leaf they want, they
demonstrate an incredible levelof skill.
Dr. Natasha Mhatre (12:51):
They don't baffle kind of willy nilly. They
try and go to the center of theleaf, which is the best
position, make this perfectlysized hole there. They'll stick
their wings through startsinging, oh, that hole isn't
just right. They might go trimthe edges a little bit and make
it the right size, and thenthey'll sing from it.
Amy Martin (13:10):
If I wanted to become an acoustical engineer, I
would likely study baffles andhow they work, and it would
involve math and physics. Buthere are these very small
animals with tiny brains whofigured it out. Natasha says
these skills are innate to sometree crickets. It's not a
learned behavior it'sgenetically programmed, but some
(13:32):
of them do have behaviors thatlook like learning, like a
craftsman, critiquing his workand making improvements as he
goes.
Dr. Natasha Mhatre (13:41):
This one guy didn't get to the center, and
he's like, this is no good. Thenhe went and chewed the second
hole and went straight for that.
Amy Martin (13:49):
Amazing. That just seems like fairly complex
problem solving. I couldn't dothat.
And the work doesn't end there.If a male tree cricket manages
to attract a female, then he hasto feed her. He produces a
secretion from a gland on hisback, which apparently tastes
really good to the ladies.Scientists call it the nuptial
(14:13):
gift, but that seems prettyeuphemistic to me. I think we
should call it a honey pot.
Dr. Natasha Mhatre (14:20):
The female climbs on top of the male. She
eats from that gland while hemates with her.
Amy Martin (14:27):
She is dining while mating.
Dr. Natasha Mhatre (14:29):
Yep, and it's like, you know, how tasty
can I make this? The longer shefeeds, the more sperm that get
transferred into her, so thehigher likelihood of him getting
babies in the next generation.So there's a lot of investment
in whatever that nuptial feedingis.
Amy Martin (14:46):
And the males are the true multi-taskers here,
because they continue to singwhile all of this is going on.
Natasha says she doesn't reallyknow why.
Dr. Natasha Mhatre (14:56):
I guess they're like, let it carry on.
Maybe then the sound willcontinue convincing the female
to stay. I don't know for sure.
Amy Martin (15:02):
Huh. Yeah, it just almost seems like logistically
difficult to do so many thingsat once. Serve a meal, have sex
Anything to keep her there.
and keep singing.
After talking with Natasha, Irealized I was hearing tree
crickets all the time withoutknowing what they were, so I
(15:25):
decided to track one down on aSeptember evening in a little
nature preserve not far from myhome in Missoula, Montana.
I'm tiptoeing through thisfield.
With my microphone out and myheadphones on, I let my ears
guide me through the tall grass.
Definitely a case of the wholethe elusive, whatever you are.
(15:51):
I take a quiet step...
That is a squirrel.
And then another...
Okay, maybe you're in heresomewhere.
And finally, I see it. It's atiny wisp of a thing with
delicate lacy wings clinging toa blade of grass. It is, indeed
(16:16):
a tree cricket, and for themoment, at least, he's alone,
but there's probably a femaletree cricket nearby, listening
like I am. Maybe she's pointinga leg at him in order to hear
him better, just like I'm doingwith the mic.
It's very light green. I'veheard it all my life here in
(16:40):
Montana, and never stopped andtried to figure out what it was.
It's beautiful.
As I sit here in the grasstaking in the song, I know that
I'm a listener within acommunity of listeners. There
(17:03):
are other people walking around.I can hear an owl across the
clearing. But what about thebranches of the Ponderosa pine
tree above me? Or the milkweedplants nearby? Or the blade of
grass itself that the treecricket is singing on? They've
all been bathed in this song allsummer long. But of course,
(17:27):
they're plants. They can't hear.They're not listening, right?
We'll have more after this shortbreak.
Matt Herlihy (17:39):
Hi, my name is Matt Herlihy, and I've been a
(17:59):
Threshold listener and donorsince season one came out in
2017. I was also one of thefirst volunteer board members of
the nonprofit organization thatmakes Threshold. Over the past
seven plus years, I've had thisunique first hand look at just
how much work it takes to makethis kind of show. I mean, the
the time, the dedication, thedetermination that's required to
tell these, these in depthstories that really make people
(18:21):
think and feel, and give peoplea sense of what it's like to
really go to places where thestories are happening, to talk
to the people who are part ofthem. It creates this rich,
immersive listening experience,And I'm telling you, that kind
of reporting, this whole kind ofshow, is not easy to make. It's
also not easy to fund. Talkabout slow, in depth, thorough.
These are not often part of theexisting models for making a
(18:42):
podcast, so it's up to peoplelike us to really make sure
Threshold can get made. Ibelieve what Threshold is doing
really matters, and if you dotoo, help them keep doing it.
Threshold's Year End fundraisingcampaign is happening right now
through December 31 and eachgift will be doubled through
NewsMatch. So if you give $25they'll receive 50. You can make
(19:03):
your one time or monthlydonation online at
thresholdpodcast.org just clickthe donate button and give what
you can. Thank you.
Dallas Taylor (19:17):
I'm Dallas Taylor, host of 20,000 Hertz, a
podcast that reveals the untoldstories behind the sounds of our
world. We've uncovered theincredible intelligence of
talking parrots.
Unknown (19:29):
Basically, bird brain was a pejorative term, and here
I had this bird that was doingthe same types of tasks the
primates.
Dallas Taylor (19:38):
We've investigated the bonding power
of music.
Unknown (19:41):
There's an intimacy there in communicating through
the medium of music that can bereally a powerful force for
bringing people together.
Dallas Taylor (19:50):
We've explored the subtle nuances of the human
voice.
Unknown (19:53):
We have to remember that humans, over many hundreds
of thousands of years ofevolution, have become extremely
attuned to the sounds of eachother's voices.
Dallas Taylor (20:01):
And we've revealed why a famous composer
wrote a piece made entirely ofsilence.
Unknown (20:06):
I think that's a really potentially quite useful and
quite profound experience tohave.
Dallas Taylor (20:11):
Subscribe to 20,000 Hertz right here in your
podcast player. I'll meet youthere.
Amy Martin (20:18):
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(20:41):
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(21:04):
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your podcasts.
(21:32):
Welcome back to Threshold, I'mAmy Martin, and let's return for
a minute to that time beforethere were any plants on land.
No grasses, no flowers, notrees. That's how our Earth has
been for most of its history,even long after plants began to
(21:52):
grow in the oceans, the worldabove the seas continued to be
dominated by rocks and dust.Plants and insects ventured into
that forbidding, lifelessterrain and transformed it
together. They've co-evolved forhundreds of millions of years,
(22:15):
and they have an endlesslycomplex and intimate set of
bonds. Like any closeconnections, their relationships
can run the whole gamut fromquiet coexistence to mutual
support to intense conflict.Plants and insects depend on
each other, and sometimes theytry to kill each other.
Dr. Heidi Appel (22:38):
Well, for most of my career, I've been studying
how plants defend themselvesagainst insects, and they do
that through chemistry.
Amy Martin (22:46):
Dr Heidi Appel is a biologist currently at the
University of Houston, and shespecializes in chemical ecology.
Dr. Heidi Appel (22:54):
Plants actually evolve to ward off their own
pests, including microorganismsthat cause disease.
Amy Martin (23:02):
When plants get attacked by insects, they can't
get up and run away. What theycan do is make and release nasty
tasting chemicals or evenpoison. And many plants are very
sophisticated chemists. They canproduce different compounds to
target specific kinds ofinvaders, and sometimes they can
even differentiate betweenintentional and accidental
(23:24):
damage. For example, when a motheats a leaf, a plant might send
out a little chemical warningshot, hoping to shoo it away.
But when a falling twig rips ahole in a leaf, that same plant
ignores it. So this is Heidi'sworld- plants, insects and
chemicals.
Dr. Heidi Appel (23:44):
So sound was not on my radar at all until I
moved to the University ofMissouri and met Rex Cocroft
after a biology seminar.
Amy Martin (23:58):
Dr Rex Cocroft is an expert in insect communication.
We met him in our last episode,and for decades, he's been
researching how some insectssend their sounds out through
the bodies of plants. So Heidiand Rex both happen to go to
this seminar and start chatting.This was in 2007.
Dr. Heidi Appel (24:19):
And I, you know, I explained what I did,
and Rex said, Well, I study theway that insects use sound
transmitted through plants tocommunicate with each other.
Amy Martin (24:27):
So here's Heidi describing her research on how
plants respond to insects, andhere's Rex describing how some
insects use plants to sendmessages to each other.
Dr. Heidi Appel (24:39):
He paused and I paused, and we kind of looked at
each other, complete strangers,you know, until now.
Amy Martin (24:47):
They were both stopped in their tracks with the
same thought.
Dr. Heidi Appel (24:50):
Oh, you don't suppose, do you that the plant
can use vibration informationfor its own purposes?
Dr. Rex Cocroft (24:59):
That's when I think, we both began to wonder
about from our own perspective,like, well, could any of this
information be relevant to theplant, and could the plant be
using any of it?
Dr. Heidi Appel (25:08):
That was the aha moment.
Amy Martin (25:11):
It seemed like a pretty radical idea, kooky even,
because if the plant was somehowusing the vibrations caused by
insects, that would mean plantscould kind of hear, maybe not
the way we hear, but stilldetect vibrations, receive
acoustic information, maybe evenfrom the animal world, and do
(25:33):
something with it.
that's really what kicked offthis study, and we've been
collaborating closely eversince.
It was already known at thatpoint that plants responded to
sounds made by humans.
Dr. Heidi Appel (25:54):
Plants will respond to single tones or to
music in all kinds of ways.
Dr. Rex Cocroft (25:59):
If you play a tone, just a pure tone, like you
could increase crop yields.There's a whole range of plant
traits that will be altered.
Dr. Heidi Appel (26:11):
The real mystery for Rex and me, because
we were trained as ecologists,was why would plants have that
Dr. Rex Cocroft (26:18):
And that's where our work came in, is that
ability?
Amy Martin (26:18):
Playing music or electronic tones to plants is
we said, well, what's anecologically relevant acoustic
very human centric. It's asking,how do plants respond to these
stimulus for a plant and whatwould be a relevant response?
sounds we're making? It's verydifferent to ask a plant or an
animal or another person, what,if any, sounds are important to you?
Unknown (26:35):
So that became really the focus of our work, relevant
sounds and relevant responses toplants.
Amy Martin (26:55):
To explore this, Heidi and Rex needed to identify
a distinctive vibration producedby an activity that mattered to
plants, and this sound quicklycame to mind. This is a
caterpillar chewing on a leaf.Rex was very familiar with these
(27:16):
sounds because they'd beendriving him bananas for a long
time. He was constantly havingto remove very hungry
caterpillars like this one fromhis plants in order to get good
recordings of tree hoppers. Sohe knew this was a conspicuous
sound produced when an insectwas doing something very
biologically relevant to theplant- eating it.
Dr. Rex Cocroft (27:40):
If there was a caterpillar on the plant feeding
on a leaf, then that's mostlywhat you're going to hear.
Amy Martin (27:46):
And Heidi knew about the chemicals plants produce
when this is happening.
Dr. Heidi Appel (27:50):
When a caterpillar bites at plant, it
gives lots of signals thatdamage has occurred. So tissue
is damaged, things leak out ofcells that triggers defense
responses, and then caterpillarsactually drool some, they have
some oral secretions when theyfeed, and that chemistry also
influences how the plantresponds.
Amy Martin (28:12):
By combining their expertise, Heidi and Rex could
try to answer a novel question,would a plant respond to the
vibrations of a chompingcaterpillar, even if there was
no actual caterpillar present?If so, that would mean that the
plant was essentially listeningto or feeling for the
caterpillar and responding.
Dr. Rex Cocroft (28:35):
To think of the plant as a kind of active
listener. I never thought aboutthat.
Amy Martin (28:42):
They got to work designing an experiment to find
out. Rex was in charge of vibes,Heidi was in charge of
chemicals. Step one, was tofigure out how to vibrate
individual leaves of a plant ina very caterpillary way, to give
the plant the experience ofbeing eaten, but without any
(29:02):
chemicals being transmitted.
Dr. Heidi Appel (29:04):
We want to just separate the effect of the
vibrations.
Amy Martin (29:09):
So Rex essentially built a little munching
caterpillar mimicry machine,minus the drool. They attached
it to some leaves, and Heidimeasured the chemical responses.
Dr. Heidi Appel (29:20):
And we found that the ones that had received
the feeding vibrations made moreof the chemical defenses than
the ones that hadn't receivedthe feeding vibrations.
Amy Martin (29:31):
Uh huh.
So it wasn't just the drool orsome other element of
caterpillar chemistry at play.The plant did, in fact, seemed
to be responding to thevibrations.
Dr. Heidi Appel (29:43):
And that surprised us. We thought, oh,
maybe it's a fluke.
Amy Martin (29:47):
Ever the careful scientists, Heidi and Rex
interrogated their results.
Dr. Rex Cocroft (29:52):
Well, it was interesting. I in no way
believed it at that point.
Amy Martin (29:56):
They didn't believe it yet, because they didn't know
if the plant was alerted by thevibrations of chewing in
particular.
Dr. Heidi Appel (30:03):
Maybe the plants just respond to anything,
you know. Maybe this isn't asignificant response, because
they'll respond to all kinds ofthings with their environment.
Amy Martin (30:12):
So they planned a second experiment. This time
they exposed the plants to threedifferent vibrations, all of
them naturally occurring in theenvironment. The munching
caterpillar, a light wind and aleaf hopper call. These little
insects are related to the treehoppers we met in our last
(30:35):
episode. The vibrations theyproduce are in a very similar
frequency to the vibrations madeby dining caterpillars, but
these are mating calls. Theydon't signal any danger to the
plant.
Dr. Heidi Appel (30:48):
So we thought that would be a pretty good test
to see how specific this plantresponse to feeding vibrations
is.
Amy Martin (30:55):
So we've got wind, tree hopper calls and
caterpillar chomps. Three kindsof vibrations with similar
frequencies, but only one ofthem signals a threat. So, if
the plants produce moredefensive chemicals in response
to the caterpillar, it wouldindicate that they're listening
or feeling for those vibrationsin particular and responding to
(31:18):
them. Rex and Heidi, vibratedthe leaves again, measured the
chemical responses again, andwaited for the results to come
in. To help eliminate bias, theyput their measurements into a
sort of code.
Dr. Heidi Appel (31:32):
We don't identify the samples as coming
from one treatment or another,so they come out as a bunch of
numbers.
Amy Martin (31:39):
Those numbers then go into a spreadsheet that
decodes the data.
Dr. Heidi Appel (31:43):
So you're sitting at a computer, you've
been sitting for four hoursgetting all the data aligned and
in the system.
Amy Martin (31:50):
And then finally, the results were revealed. The
plants that had received thecaterpillar vibrations had
produced more defensivechemicals than the others.
Dr. Heidi Appel (32:04):
I remember sitting there screaming, there's
a difference here and not here!And I think I might have even
gotten up and done a happydance. And of course, right away
I'm texting Rex.
Amy Martin (32:19):
The plants were listening out for the vibrations
that mattered the most.
Dr. Heidi Appel (32:25):
So yeah, it was very, a very exciting moment.
And, you know, I I feel lucky ifI had, I've had one of those
this exciting in my wholescientific career. And if I
never have another one, I'll diehappy.
Amy Martin (32:42):
Because this really hadn't, no one knew this before.
You added something new to ourscientific knowledge of plants.
Dr. Heidi Appel (32:51):
Yes, we did. Because even though people knew
that plants could respond tothese other synthetic tones or
music, right, the fact that hecould discriminate between a
biologically relevant sound andone that wasn't, was a real big
advance in our understanding.
Amy Martin (33:13):
It's not very often that you get to talk to people
who've made major scientificbreakthroughs like this, and as
a scientist, it's not very oftenthat you get to be one of those
people.
Do you feel a little bit likeGalileo looking through the
telescope for the first time oflike, oh my gosh!
Dr. Heidi Appel (33:32):
It does cause me to look at the world very
differently, but I don't thinkwe're going to have the impact
that Galileo.
Amy Martin (33:39):
Maybe not, but Rex and Heidi's discovery did make a
big splash. It was covered innewspapers around the world, and
they got interviewed countlesstimes. It was all pretty
shocking to them. Rex says whenthey started down this path, he
was very skeptical that theywould find anything of interest.
The idea of plants being able toengage in a sort of dialog with
(34:02):
animals, just seemed too outthere.
Dr. Rex Cocroft (34:05):
But it now has become firmly established in my
mind that if you're studyingcommunication through plants,
that one of the potentialreceivers of these signals is
the plant, and that we need tothink about that.
Amy Martin (34:19):
Now that we know that plants can detect and
respond to biologically relevantsounds like munching
caterpillars, it seems kind ofsurprising that it took us this
long to figure it out, andindeed, from the perspective of
many indigenous people, researchlike this is not so much a
discovery of new information asit is an incorporation of wisdom
(34:40):
that's been there all along. Butby testing this question inside
the framework of Westernscience, Rex and Heidi helped to
bridge that gap betweendifferent ways of knowing.
They've provided hard evidencefor plant listening, a whole
layer of relationship reallyhappening all around us every
day. Scientists knew that plantsand animals compete and
(35:04):
cooperate, now they know thatthey also converse. They've gone
from assuming sound wasirrelevant to plants to
understanding that plants areactually super receivers of
sounds and vibrations.
Dr. Rex Cocroft (35:18):
The soundscape, or the vibroscape, if you will,
of a living plant is one of themost complex soundscapes that
there is.
Amy Martin (35:27):
Leaves capture the airborne sound environment.
Sounds in the soil can move upthrough the roots.
Dr. Rex Cocroft (35:33):
And then you have all of the incredible
sounds or vibrations created byinsects and other animals that
are in contact with the plant.
Amy Martin (35:42):
Understanding this, the question shifts from why
would plants respond to sound towhy wouldn't they?
I'm curious if you feel moreclosely connected to plants
because of this, because you'vebeen listening to insects for
decades now, and here, turns outplants are also listening. Does
(36:04):
it give you more of a sense ofkinship with them?
Dr. Rex Cocroft (36:07):
I think it does. I would say that it does.
There's some physicalinformation out there that I'm
really interested in, that theplant also has a stake in. So
yes, it does provide a perhaps alittle bit of a fellow feeling.
Amy Martin (36:22):
If you hear some wariness in Rex's voice, I think
it's a reflection of the factthat people can get really
polarized around plants. On oneside are hardcore mystics who
insist on things like plants canread minds and predict the
future. On the other aremilitant guardians of the ivory
tower who seem eager to attackanyone who proposes a slightly
(36:46):
out of the box research idea.But there are many people who
are working in the exciting andoften uncomfortable territory
between these two fairly rigidcamps, people like Heidi, Rex
and some scientists we'll meetin our next episode too, who are
asking brave questions and doingsolid evidence based work to try
(37:08):
to answer them.
Dr. Rex Cocroft (37:09):
I would say, in some ways, plants do almost
everything that animals do. Theyjust do it really differently.
Amy Martin (37:16):
We're walking around in the world that plants made.
Every creature on earth, fromDolly Parton on down, depends on
them for survival.Intellectually, I know this. I
know my survival rests on allthese other living things that I
often ignore, but the work ofthese scientists helps me feel
(37:38):
it.
Dr. Heidi Appel (37:40):
When we can identify with other living
organisms, it creates an empathyin us that I think will allow us
to be better stewards of theplanet.
Amy Martin (37:51):
It feels like it makes plants less other.
Dr. Heidi Appel (37:55):
It's this common sense of being alive and
being interconnected, which Ithink is really important to our
development as humans.
Amy Martin (38:09):
Maybe someday we'll learn that plants do have
supernatural powers, but in themeantime, just the natural seems
wondrous enough.
(38:34):
This episode of Threshold waswritten, reported and produced
by me, Amy Martin, with helpfrom Erika Janik and Sam Moore.
Music by Todd Sickafoose. Postproduction by Alan Douches. Fact
checking by Sam Moore. Specialthanks to Natasha Mhatre, Rex
Cocroft and Heidi Appel for someof the insect sounds you heard
(38:56):
in this episode, and to ChrisPeiffer at WGTE Public Media.
Threshold is made by AuricleProductions, a non profit
organization powered by listenerdonations. Deneen Weiske is our
executive director. You can findout more about our show at thresholdpodcast.org.
We're in eastern Tennessee half a billion years
(00:03):
ago. The land we now call theSmoky Mountains is almost
totally covered by a shallowsea, and life on Earth is still
mostly confined to the oceans,until a tiny moss does something
remarkable. It finds a footholdon some rocks and stays there.
(00:29):
It's an early pioneer into thebarren world above the waves, an
adventurer that helps to turnthe terrestrial world green. Now
fast forward hundreds ofmillions of years to 1946. Just
down river from the very spotwhere that ancient moss lived
(00:53):
and died, another Trailblazer isborn.
Dolly Parton (00:56):
Sitting on the front porch on a summer
afternoon.
Amy Martin (01:02):
Dolly Parton.
Dolly Parton (01:03):
In a straight back chair on two legs, leaned
against the wall.
Amy Martin (01:10):
Raised in a one room cabin with 11 siblings, Dolly
went on to write thousands ofsongs, many of them full of
references to the wild thingsshe grew up with. This one
called "My Tennessee MountainHome" recounts a childhood
filled with butterflies, birds,wildflowers and crickets.
Dolly Parton (01:34):
In my Tennessee mountain home, crickets sing in
the fields nearby.
Amy Martin (01:45):
So when a geologist unearthed that ancient moss near
Dolly's home and learned that itmight be one of the oldest
fossilized land plants everdiscovered, he named it
Dollyphyton boucotti in herhonor. A moss and a musician, a
plant and an animal. Thisconnection between flora and
(02:09):
fauna is fundamental to thesoundscape of our planet and the
flourishing of life overall.Because as plants began to
emerge out of the sea, someadventurous animals followed
suit. They were probablyscorpion-like creatures.
Arthropods, related to ourmodern insects and spiders, and
(02:31):
they were the very first animalsto scuttle across the untouched
beaches of the terrestrialworld. This new realm must have
been shockingly bright and dryfor the plants and the animals,
but finding no other life, theywent forth and multiplied and
(02:51):
multiplied and multiplied. Afterthe mosses and lichens came
ferns and trees, and about 150million years ago, came the
miracle of flowers, painting theworld in color and pollinated by
beetles, moths and other wingedthings. And as the world got
(03:12):
greener, it got louder. Cicadascalled from the branches,
crickets made choruses in theleaves. Insects invented song.
They laid down the very firstnotes of what would later become
a symphony of terrestrial sound.But they couldn't have done it
alone. Without plants, therewould be no animals, no songs at
(03:36):
all. So without Dollyphyton,there might never have been a
Dolly Parton. Welcome toThreshold, I'm Amy Martin, and
in this episode, we're going toexplore the intertwined acoustic
lives of plants and insects.
(04:20):
So I want to start by naming thedung beetle in the room here.
Both plants and insects arethings that people often ignore.
We just take it for granted thatplants spend their lives giving
us breathable air, stabilizingour climate and providing the
basis for every bite of food weconsume, and we forget that
(04:42):
insects are arguably thetoughest animals our world has
ever known, that they've made itthrough multiple mass
extinctions, major climaticchanges and a total
rearrangement of the continents,and they're also just, well, Wil
Hershberger says it best.
Wil Hershberger (05:01):
Many of our singing insects are handsome, if
not downright beautiful. Fromthe tiny trigs and ground
crickets through the meadow andconehead katydids to the true
and false katydids, there's analmost endless variety of
shapes, colors and sounds toexplore.
Amy Martin (05:18):
That's Wil introducing people to the
website songsofinsects.com and Ichallenge you to visit this site
and not fall in love with atleast one insect. It is chock
full of pictures, videos,information and sound recordings
of a huge array of six leggedsingers. There's the slow,
(05:39):
tinkling trig, the confusedground cricket, the scissor
grinder cicada and the slightlymusical conehead, kind of a
passive aggressive name, butsorry, coneheads, I think it's
(05:59):
accurate. Insects make thousandsof different kinds of sounds,
and they also have an impressivevariety of ways to listen.
Dr. Natasha Mhatre (06:12):
The fun thing about insects is that they
have evolved hearing at least 17times independently, so they've
invented ears over and over andover again.
Amy Martin (06:25):
This is Dr Natasha Mhatre. She's the one who told
us about how spider webs can beears in our last episode. She's
based at the University ofWestern Ontario, and she
researches invertebrateneurobiology. In other words,
she's an expert in bug brainsand especially how insects and
(06:45):
spiders process sound. She says,insects grow ears in all sorts
of places on their bodies.
Dr. Natasha Mhatre (06:53):
Grasshoppers have them on the abdomen, so in
one of the segments of theirbody. Crickets have them on
their forelegs, so they move theears as they walk.
Amy Martin (07:03):
Cool!
Natasha says one kind of motheven grows an ear on its mouth.
So the thing it eats with isalso the thing it hears with.
Dr. Natasha Mhatre (07:14):
I would not want to be this moth because,
like it would sound awful.
Amy Martin (07:19):
Arthropods currently make up more than 80% of Earth's
animal species, on land and inthe sea, and insects are the
largest group of animals in thatcategory. All of which is to say
it would be impossible to do afull survey of all the sonic
wonders of the arthropod world.So I decided to focus on just
one especially creativespecimen, the tree cricket. The
(07:43):
delicate green cousin of themuch burlier field cricket.
Dr. Natasha Mhatre (07:47):
They're actually quite slender. They
look like blades of grass. Andthe males have these like
lovely, beautiful glass, likewings. And when they sing, their
wings are flipped up and they'realmost completely transparent.
They just look so pretty.
Amy Martin (08:03):
Is it fair to say that you have a special
relationship with tree crickets?
Dr. Natasha Mhatre (08:06):
I have a special relationship with tree
crickets.
Amy Martin (08:12):
Tree crickets punch way, way above their weight
class in terms of makingthemselves heard. They are
really small and they can bereally loud.
Dr. Natasha Mhatre (08:22):
They're super cool. They live pretty
much everywhere. There's treecrickets in Australia, there's
three crickets all over Asia.North America, South America.
They're in Africa. I don't thinkthere's any in the Antarctic,
but that's it. So they'reeverywhere this, you know, it's
lots of species, so you canprobably find a tree cricket
somewhere close to you.
Amy Martin (08:41):
Natasha says it's a common misconception that they
make their sounds by rubbingtheir legs together, but tree
crickets actually sing withtheir wings. One wing has a row
of pegs on it called the file,and on the other there's a tiny
little lump called the plectrum.When the tree cricket rubs its
(09:03):
wings together, the plectrumruns down the file like a guitar
pick running down the strings.It's called stridulation, and
when I slow the recording waydown, you can hear each
individual wing beat. Treecrickets are actually moving
their wings up to 100 times persecond, turning the sound of
(09:24):
their wing beats into anacoustic blur, at least our
ears. There's quite a bit ofvariety in tree cricket song.
Some make sustained trills.Others like to lay down a
groove, but all of this highspeed wing strumming is
essentially a love song. Malesdo it to attract females, and
(09:49):
the gals are choosy. They listento the songs not only to locate
their suitors among the leaves,but also to assess them.
Consider the situation of tworomantically inclined tree
crickets. Two almost weightless,little beings living in a
dangerous world. With predatorsall around ready to turn them
(10:11):
into a tasty meal, hiding isessential. Their bodies have
evolved to blend in among thestems and leaves, and they're
very good at holding very still,but that means tree crickets are
hidden from each other too,until the male starts to sing.
His song is an acoustic beaconcutting through the night,
(10:35):
broadcasting his location.Instead of a profile picture, he
has a profile song, and insteadof swiping left or right, the
females, with two ears locatedon two different legs, listen to
the serenades and hop left orright, slowly working their way
toward the fellow of theirchoice.
Dr. Natasha Mhatre (10:55):
You know the purity of the tone the animal
produces tells you somethingabout the condition of the
wings. So is this an old animal?Is this a young animal? Are half
his teeth missing?
Amy Martin (11:09):
Wow. So we got like, a bunch of judgmental lady
crickets.
Dr. Natasha Mhatre (11:12):
Totally. Well, they're like, if I'm gonna
spend the time walking up toyou, wherever the hell you are
and finding you, you better beworth my while.
Amy Martin (11:22):
And I'm gonna tell that by the quality of your,
your plucking.
Dr. Natasha Mhatre (11:27):
That plus just how long you go like
crickets that you know have alittle bit of stamina do better.
Yeah.
Amy Martin (11:36):
Evolution is cruel.
So for the males, it's all aboutgetting heard, and sometimes to
increase their chances, theyactually build their own
cricket-sized megaphones usingall local recyclable materials
to boot. They're called baffles.And male tree crickets make them
(11:59):
out of leaves. They chew holesinto them and stick their heads
through, and when theystratulate Their wings, the leaf
turns up the volume on theirsongs.
Dr. Natasha Mhatre (12:08):
Think of making your wings artificially
bigger.
Amy Martin (12:11):
Natasha ran experiments to test the
cricket's baffle-makingabilities, and she discovered
that they're almost freakishlygood at it. Even before they
start the building process,they're somehow calculating
which leaves to use as rawmaterials.
Dr. Natasha Mhatre (12:25):
If you give them a small leaf, they probably
won't make a baffle. If you givethem a nice, big one that really
gives them a lot of benefit,they will make it. They don't
even need to sing on the leaf toknow if it's the big one. They
seem to have some way offiguring it out in the darkness,
they ignore the small leaf. Theygo straight for the big one.
Amy Martin (12:45):
And once they've chosen the leaf they want, they
demonstrate an incredible levelof skill.
Dr. Natasha Mhatre (12:51):
They don't baffle kind of willy nilly. They
try and go to the center of theleaf, which is the best
position, make this perfectlysized hole there. They'll stick
their wings through startsinging, oh, that hole isn't
just right. They might go trimthe edges a little bit and make
it the right size, and thenthey'll sing from it.
Amy Martin (13:10):
If I wanted to become an acoustical engineer, I
would likely study baffles andhow they work, and it would
involve math and physics. Buthere are these very small
animals with tiny brains whofigured it out. Natasha says
these skills are innate to sometree crickets. It's not a
learned behavior it'sgenetically programmed, but some
(13:32):
of them do have behaviors thatlook like learning, like a
craftsman, critiquing his workand making improvements as he
goes.
Dr. Natasha Mhatre (13:41):
This one guy didn't get to the center, and
he's like, this is no good. Thenhe went and chewed the second
hole and went straight for that.
Amy Martin (13:49):
Amazing. That just seems like fairly complex
problem solving. I couldn't dothat.
And the work doesn't end there.If a male tree cricket manages
to attract a female, then he hasto feed her. He produces a
secretion from a gland on hisback, which apparently tastes
really good to the ladies.Scientists call it the nuptial
(14:13):
gift, but that seems prettyeuphemistic to me. I think we
should call it a honey pot.
Dr. Natasha Mhatre (14:20):
The female climbs on top of the male. She
eats from that gland while hemates with her.
Amy Martin (14:27):
She is dining while mating.
Dr. Natasha Mhatre (14:29):
Yep, and it's like, you know, how tasty
can I make this? The longer shefeeds, the more sperm that get
transferred into her, so thehigher likelihood of him getting
babies in the next generation.So there's a lot of investment
in whatever that nuptial feedingis.
Amy Martin (14:46):
And the males are the true multi-taskers here,
because they continue to singwhile all of this is going on.
Natasha says she doesn't reallyknow why.
Dr. Natasha Mhatre (14:56):
I guess they're like, let it carry on.
Maybe then the sound willcontinue convincing the female
to stay. I don't know for sure.
Amy Martin (15:02):
Huh. Yeah, it just almost seems like logistically
difficult to do so many thingsat once. Serve a meal, have sex
Anything to keep her there.
and keep singing.
After talking with Natasha, Irealized I was hearing tree
crickets all the time withoutknowing what they were, so I
(15:25):
decided to track one down on aSeptember evening in a little
nature preserve not far from myhome in Missoula, Montana.
I'm tiptoeing through thisfield.
With my microphone out and myheadphones on, I let my ears
guide me through the tall grass.
Definitely a case of the wholethe elusive, whatever you are.
(15:51):
I take a quiet step...
That is a squirrel.
And then another...
Okay, maybe you're in heresomewhere.
And finally, I see it. It's atiny wisp of a thing with
delicate lacy wings clinging toa blade of grass. It is, indeed
(16:16):
a tree cricket, and for themoment, at least, he's alone,
but there's probably a femaletree cricket nearby, listening
like I am. Maybe she's pointinga leg at him in order to hear
him better, just like I'm doingwith the mic.
It's very light green. I'veheard it all my life here in
(16:40):
Montana, and never stopped andtried to figure out what it was.
It's beautiful.
As I sit here in the grasstaking in the song, I know that
I'm a listener within acommunity of listeners. There
(17:03):
are other people walking around.I can hear an owl across the
clearing. But what about thebranches of the Ponderosa pine
tree above me? Or the milkweedplants nearby? Or the blade of
grass itself that the treecricket is singing on? They've
all been bathed in this song allsummer long. But of course,
(17:27):
they're plants. They can't hear.They're not listening, right?
We'll have more after this shortbreak.
Matt Herlihy (17:39):
Hi, my name is Matt Herlihy, and I've been a
(17:59):
Threshold listener and donorsince season one came out in
2017. I was also one of thefirst volunteer board members of
the nonprofit organization thatmakes Threshold. Over the past
seven plus years, I've had thisunique first hand look at just
how much work it takes to makethis kind of show. I mean, the
the time, the dedication, thedetermination that's required to
tell these, these in depthstories that really make people
(18:21):
think and feel, and give peoplea sense of what it's like to
really go to places where thestories are happening, to talk
to the people who are part ofthem. It creates this rich,
immersive listening experience,And I'm telling you, that kind
of reporting, this whole kind ofshow, is not easy to make. It's
also not easy to fund. Talkabout slow, in depth, thorough.
These are not often part of theexisting models for making a
(18:42):
podcast, so it's up to peoplelike us to really make sure
Threshold can get made. Ibelieve what Threshold is doing
really matters, and if you dotoo, help them keep doing it.
Threshold's Year End fundraisingcampaign is happening right now
through December 31 and eachgift will be doubled through
NewsMatch. So if you give $25they'll receive 50. You can make
(19:03):
your one time or monthlydonation online at
thresholdpodcast.org just clickthe donate button and give what
you can. Thank you.
Dallas Taylor (19:17):
I'm Dallas Taylor, host of 20,000 Hertz, a
podcast that reveals the untoldstories behind the sounds of our
world. We've uncovered theincredible intelligence of
talking parrots.
Unknown (19:29):
Basically, bird brain was a pejorative term, and here
I had this bird that was doingthe same types of tasks the
primates.
Dallas Taylor (19:38):
We've investigated the bonding power
of music.
Unknown (19:41):
There's an intimacy there in communicating through
the medium of music that can bereally a powerful force for
bringing people together.
Dallas Taylor (19:50):
We've explored the subtle nuances of the human
voice.
Unknown (19:53):
We have to remember that humans, over many hundreds
of thousands of years ofevolution, have become extremely
attuned to the sounds of eachother's voices.
Dallas Taylor (20:01):
And we've revealed why a famous composer
wrote a piece made entirely ofsilence.
Unknown (20:06):
I think that's a really potentially quite useful and
quite profound experience tohave.
Dallas Taylor (20:11):
Subscribe to 20,000 Hertz right here in your
podcast player. I'll meet youthere.
Amy Martin (20:18):
Hi Threshold listeners. Do you ever find
yourself wondering whatbusinesses are doing and what
more they should do to confrontclimate change? Then you should
check out Climate Rising, theaward winning podcast from
Harvard Business School. ClimateRising gives you a behind the
scenes look at how top businessleaders are taking on the
challenge of climate change. Theshow covers cutting edge
(20:41):
solutions, from leveraging AIand carbon markets to sharing
stories that inspire climateaction. Recent episodes feature
insightful conversations withleaders like Netflix's first
sustainability officer, EmmaStewart, who discusses how the
global entertainment giant usesits platform to promote climate
awareness. You'll also hear fromCNN chief climate correspondent,
(21:04):
Bill Weir, about the importanceof integrating climate change
into news coverage. Each episodedives deep into the challenges
and opportunities that climatechange presents to entrepreneurs
and innovators. Listen toClimate Rising every other
Wednesday on Apple podcasts,Spotify, or wherever you get
your podcasts.
(21:32):
Welcome back to Threshold, I'mAmy Martin, and let's return for
a minute to that time beforethere were any plants on land.
No grasses, no flowers, notrees. That's how our Earth has
been for most of its history,even long after plants began to
(21:52):
grow in the oceans, the worldabove the seas continued to be
dominated by rocks and dust.Plants and insects ventured into
that forbidding, lifelessterrain and transformed it
together. They've co-evolved forhundreds of millions of years,
(22:15):
and they have an endlesslycomplex and intimate set of
bonds. Like any closeconnections, their relationships
can run the whole gamut fromquiet coexistence to mutual
support to intense conflict.Plants and insects depend on
each other, and sometimes theytry to kill each other.
Dr. Heidi Appel (22:38):
Well, for most of my career, I've been studying
how plants defend themselvesagainst insects, and they do
that through chemistry.
Amy Martin (22:46):
Dr Heidi Appel is a biologist currently at the
University of Houston, and shespecializes in chemical ecology.
Dr. Heidi Appel (22:54):
Plants actually evolve to ward off their own
pests, including microorganismsthat cause disease.
Amy Martin (23:02):
When plants get attacked by insects, they can't
get up and run away. What theycan do is make and release nasty
tasting chemicals or evenpoison. And many plants are very
sophisticated chemists. They canproduce different compounds to
target specific kinds ofinvaders, and sometimes they can
even differentiate betweenintentional and accidental
(23:24):
damage. For example, when a motheats a leaf, a plant might send
out a little chemical warningshot, hoping to shoo it away.
But when a falling twig rips ahole in a leaf, that same plant
ignores it. So this is Heidi'sworld- plants, insects and
chemicals.
Dr. Heidi Appel (23:44):
So sound was not on my radar at all until I
moved to the University ofMissouri and met Rex Cocroft
after a biology seminar.
Amy Martin (23:58):
Dr Rex Cocroft is an expert in insect communication.
We met him in our last episode,and for decades, he's been
researching how some insectssend their sounds out through
the bodies of plants. So Heidiand Rex both happen to go to
this seminar and start chatting.This was in 2007.
Dr. Heidi Appel (24:19):
And I, you know, I explained what I did,
and Rex said, Well, I study theway that insects use sound
transmitted through plants tocommunicate with each other.
Amy Martin (24:27):
So here's Heidi describing her research on how
plants respond to insects, andhere's Rex describing how some
insects use plants to sendmessages to each other.
Dr. Heidi Appel (24:39):
He paused and I paused, and we kind of looked at
each other, complete strangers,you know, until now.
Amy Martin (24:47):
They were both stopped in their tracks with the
same thought.
Dr. Heidi Appel (24:50):
Oh, you don't suppose, do you that the plant
can use vibration informationfor its own purposes?
Dr. Rex Cocroft (24:59):
That's when I think, we both began to wonder
about from our own perspective,like, well, could any of this
information be relevant to theplant, and could the plant be
using any of it?
Dr. Heidi Appel (25:08):
That was the aha moment.
Amy Martin (25:11):
It seemed like a pretty radical idea, kooky even,
because if the plant was somehowusing the vibrations caused by
insects, that would mean plantscould kind of hear, maybe not
the way we hear, but stilldetect vibrations, receive
acoustic information, maybe evenfrom the animal world, and do
(25:33):
something with it.
that's really what kicked offthis study, and we've been
collaborating closely eversince.
It was already known at thatpoint that plants responded to
sounds made by humans.
Dr. Heidi Appel (25:54):
Plants will respond to single tones or to
music in all kinds of ways.
Dr. Rex Cocroft (25:59):
If you play a tone, just a pure tone, like you
could increase crop yields.There's a whole range of plant
traits that will be altered.
Dr. Heidi Appel (26:11):
The real mystery for Rex and me, because
we were trained as ecologists,was why would plants have that
Dr. Rex Cocroft (26:18):
And that's where our work came in, is that
ability?
Amy Martin (26:18):
Playing music or electronic tones to plants is
we said, well, what's anecologically relevant acoustic
very human centric. It's asking,how do plants respond to these
stimulus for a plant and whatwould be a relevant response?
sounds we're making? It's verydifferent to ask a plant or an
animal or another person, what,if any, sounds are important to you?
Unknown (26:35):
So that became really the focus of our work, relevant
sounds and relevant responses toplants.
Amy Martin (26:55):
To explore this, Heidi and Rex needed to identify
a distinctive vibration producedby an activity that mattered to
plants, and this sound quicklycame to mind. This is a
caterpillar chewing on a leaf.Rex was very familiar with these
(27:16):
sounds because they'd beendriving him bananas for a long
time. He was constantly havingto remove very hungry
caterpillars like this one fromhis plants in order to get good
recordings of tree hoppers. Sohe knew this was a conspicuous
sound produced when an insectwas doing something very
biologically relevant to theplant- eating it.
Dr. Rex Cocroft (27:40):
If there was a caterpillar on the plant feeding
on a leaf, then that's mostlywhat you're going to hear.
Amy Martin (27:46):
And Heidi knew about the chemicals plants produce
when this is happening.
Dr. Heidi Appel (27:50):
When a caterpillar bites at plant, it
gives lots of signals thatdamage has occurred. So tissue
is damaged, things leak out ofcells that triggers defense
responses, and then caterpillarsactually drool some, they have
some oral secretions when theyfeed, and that chemistry also
influences how the plantresponds.
Amy Martin (28:12):
By combining their expertise, Heidi and Rex could
try to answer a novel question,would a plant respond to the
vibrations of a chompingcaterpillar, even if there was
no actual caterpillar present?If so, that would mean that the
plant was essentially listeningto or feeling for the
caterpillar and responding.
Dr. Rex Cocroft (28:35):
To think of the plant as a kind of active
listener. I never thought aboutthat.
Amy Martin (28:42):
They got to work designing an experiment to find
out. Rex was in charge of vibes,Heidi was in charge of
chemicals. Step one, was tofigure out how to vibrate
individual leaves of a plant ina very caterpillary way, to give
the plant the experience ofbeing eaten, but without any
(29:02):
chemicals being transmitted.
Dr. Heidi Appel (29:04):
We want to just separate the effect of the
vibrations.
Amy Martin (29:09):
So Rex essentially built a little munching
caterpillar mimicry machine,minus the drool. They attached
it to some leaves, and Heidimeasured the chemical responses.
Dr. Heidi Appel (29:20):
And we found that the ones that had received
the feeding vibrations made moreof the chemical defenses than
the ones that hadn't receivedthe feeding vibrations.
Amy Martin (29:31):
Uh huh.
So it wasn't just the drool orsome other element of
caterpillar chemistry at play.The plant did, in fact, seemed
to be responding to thevibrations.
Dr. Heidi Appel (29:43):
And that surprised us. We thought, oh,
maybe it's a fluke.
Amy Martin (29:47):
Ever the careful scientists, Heidi and Rex
interrogated their results.
Dr. Rex Cocroft (29:52):
Well, it was interesting. I in no way
believed it at that point.
Amy Martin (29:56):
They didn't believe it yet, because they didn't know
if the plant was alerted by thevibrations of chewing in
particular.
Dr. Heidi Appel (30:03):
Maybe the plants just respond to anything,
you know. Maybe this isn't asignificant response, because
they'll respond to all kinds ofthings with their environment.
Amy Martin (30:12):
So they planned a second experiment. This time
they exposed the plants to threedifferent vibrations, all of
them naturally occurring in theenvironment. The munching
caterpillar, a light wind and aleaf hopper call. These little
insects are related to the treehoppers we met in our last
(30:35):
episode. The vibrations theyproduce are in a very similar
frequency to the vibrations madeby dining caterpillars, but
these are mating calls. Theydon't signal any danger to the
plant.
Dr. Heidi Appel (30:48):
So we thought that would be a pretty good test
to see how specific this plantresponse to feeding vibrations
is.
Amy Martin (30:55):
So we've got wind, tree hopper calls and
caterpillar chomps. Three kindsof vibrations with similar
frequencies, but only one ofthem signals a threat. So, if
the plants produce moredefensive chemicals in response
to the caterpillar, it wouldindicate that they're listening
or feeling for those vibrationsin particular and responding to
(31:18):
them. Rex and Heidi, vibratedthe leaves again, measured the
chemical responses again, andwaited for the results to come
in. To help eliminate bias, theyput their measurements into a
sort of code.
Dr. Heidi Appel (31:32):
We don't identify the samples as coming
from one treatment or another,so they come out as a bunch of
numbers.
Amy Martin (31:39):
Those numbers then go into a spreadsheet that
decodes the data.
Dr. Heidi Appel (31:43):
So you're sitting at a computer, you've
been sitting for four hoursgetting all the data aligned and
in the system.
Amy Martin (31:50):
And then finally, the results were revealed. The
plants that had received thecaterpillar vibrations had
produced more defensivechemicals than the others.
Dr. Heidi Appel (32:04):
I remember sitting there screaming, there's
a difference here and not here!And I think I might have even
gotten up and done a happydance. And of course, right away
I'm texting Rex.
Amy Martin (32:19):
The plants were listening out for the vibrations
that mattered the most.
Dr. Heidi Appel (32:25):
So yeah, it was very, a very exciting moment.
And, you know, I I feel lucky ifI had, I've had one of those
this exciting in my wholescientific career. And if I
never have another one, I'll diehappy.
Amy Martin (32:42):
Because this really hadn't, no one knew this before.
You added something new to ourscientific knowledge of plants.
Dr. Heidi Appel (32:51):
Yes, we did. Because even though people knew
that plants could respond tothese other synthetic tones or
music, right, the fact that hecould discriminate between a
biologically relevant sound andone that wasn't, was a real big
advance in our understanding.
Amy Martin (33:13):
It's not very often that you get to talk to people
who've made major scientificbreakthroughs like this, and as
a scientist, it's not very oftenthat you get to be one of those
people.
Do you feel a little bit likeGalileo looking through the
telescope for the first time oflike, oh my gosh!
Dr. Heidi Appel (33:32):
It does cause me to look at the world very
differently, but I don't thinkwe're going to have the impact
that Galileo.
Amy Martin (33:39):
Maybe not, but Rex and Heidi's discovery did make a
big splash. It was covered innewspapers around the world, and
they got interviewed countlesstimes. It was all pretty
shocking to them. Rex says whenthey started down this path, he
was very skeptical that theywould find anything of interest.
The idea of plants being able toengage in a sort of dialog with
(34:02):
animals, just seemed too outthere.
Dr. Rex Cocroft (34:05):
But it now has become firmly established in my
mind that if you're studyingcommunication through plants,
that one of the potentialreceivers of these signals is
the plant, and that we need tothink about that.
Amy Martin (34:19):
Now that we know that plants can detect and
respond to biologically relevantsounds like munching
caterpillars, it seems kind ofsurprising that it took us this
long to figure it out, andindeed, from the perspective of
many indigenous people, researchlike this is not so much a
discovery of new information asit is an incorporation of wisdom
(34:40):
that's been there all along. Butby testing this question inside
the framework of Westernscience, Rex and Heidi helped to
bridge that gap betweendifferent ways of knowing.
They've provided hard evidencefor plant listening, a whole
layer of relationship reallyhappening all around us every
day. Scientists knew that plantsand animals compete and
(35:04):
cooperate, now they know thatthey also converse. They've gone
from assuming sound wasirrelevant to plants to
understanding that plants areactually super receivers of
sounds and vibrations.
Dr. Rex Cocroft (35:18):
The soundscape, or the vibroscape, if you will,
of a living plant is one of themost complex soundscapes that
there is.
Amy Martin (35:27):
Leaves capture the airborne sound environment.
Sounds in the soil can move upthrough the roots.
Dr. Rex Cocroft (35:33):
And then you have all of the incredible
sounds or vibrations created byinsects and other animals that
are in contact with the plant.
Amy Martin (35:42):
Understanding this, the question shifts from why
would plants respond to sound towhy wouldn't they?
I'm curious if you feel moreclosely connected to plants
because of this, because you'vebeen listening to insects for
decades now, and here, turns outplants are also listening. Does
(36:04):
it give you more of a sense ofkinship with them?
Dr. Rex Cocroft (36:07):
I think it does. I would say that it does.
There's some physicalinformation out there that I'm
really interested in, that theplant also has a stake in. So
yes, it does provide a perhaps alittle bit of a fellow feeling.
Amy Martin (36:22):
If you hear some wariness in Rex's voice, I think
it's a reflection of the factthat people can get really
polarized around plants. On oneside are hardcore mystics who
insist on things like plants canread minds and predict the
future. On the other aremilitant guardians of the ivory
tower who seem eager to attackanyone who proposes a slightly
(36:46):
out of the box research idea.But there are many people who
are working in the exciting andoften uncomfortable territory
between these two fairly rigidcamps, people like Heidi, Rex
and some scientists we'll meetin our next episode too, who are
asking brave questions and doingsolid evidence based work to try
(37:08):
to answer them.
Dr. Rex Cocroft (37:09):
I would say, in some ways, plants do almost
everything that animals do. Theyjust do it really differently.
Amy Martin (37:16):
We're walking around in the world that plants made.
Every creature on earth, fromDolly Parton on down, depends on
them for survival.Intellectually, I know this. I
know my survival rests on allthese other living things that I
often ignore, but the work ofthese scientists helps me feel
(37:38):
it.
Dr. Heidi Appel (37:40):
When we can identify with other living
organisms, it creates an empathyin us that I think will allow us
to be better stewards of theplanet.
Amy Martin (37:51):
It feels like it makes plants less other.
Dr. Heidi Appel (37:55):
It's this common sense of being alive and
being interconnected, which Ithink is really important to our
development as humans.
Amy Martin (38:09):
Maybe someday we'll learn that plants do have
supernatural powers, but in themeantime, just the natural seems
wondrous enough.
(38:34):
This episode of Threshold waswritten, reported and produced
by me, Amy Martin, with helpfrom Erika Janik and Sam Moore.
Music by Todd Sickafoose. Postproduction by Alan Douches. Fact
checking by Sam Moore. Specialthanks to Natasha Mhatre, Rex
Cocroft and Heidi Appel for someof the insect sounds you heard
(38:56):
in this episode, and to ChrisPeiffer at WGTE Public Media.
Threshold is made by AuricleProductions, a non profit
organization powered by listenerdonations. Deneen Weiske is our
executive director. You can findout more about our show at thresholdpodcast.org.
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