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TED2014

Sara Lewis: The loves and lies of fireflies

March 20, 2014

Biologist Sara Lewis has spent the past 20 years getting to the bottom of the magic and wonder of fireflies. In this charming talk, she tells us how and why the beetles produce their silent sparks, what happens when two fireflies have sex, and why one group of females is known as the firefly vampire. (It's not pretty.) Find out more astonishing facts about fireflies in Lewis' footnotes, below.

Sara Lewis - Firefly specialist
Evolutionary ecologist Sara Lewis digs deep into firefly mating rituals to uncover a world of secret languages and strange gifts in these silent sparks. Full bio

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Double-click the English subtitles below to play the video.
As a scientist, and also as a human being,
00:12
I've been trying to make myself
00:15
susceptible to wonder.
00:17
I think Jason Webley last night called it
00:21
"conspiring to be part of the magic."
00:24
So it's fortunate that my career as a biologist
00:28
lets me dive deeply into the lives
00:31
of some truly wondrous creatures
00:33
that share our planet:
00:36
fireflies.
00:38
Now, for many of you, I know that fireflies
00:40
might conjure up some really great memories:
00:42
childhood, summertime,
00:45
even other TED Talks.
00:48
Maybe something like this.
00:50
My seduction into the world of fireflies
00:57
began when I was back in graduate school.
00:59
One evening, I was sitting out in my backyard
01:03
in North Carolina,
01:06
and suddenly, these silent sparks
01:08
rose up all around me,
01:13
and I began to wonder:
01:15
How do these creatures make light,
01:16
and what's with all this flashing?
01:19
Are they talking to one another?
01:21
And what happens after the lights go out?
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I've been lucky enough to answer
01:26
some of these questions
01:27
as I've explored this nocturnal world.
01:28
Now if you've ever seen
01:32
or even heard about fireflies,
01:35
then you'll know how magically they can transform
01:37
our everyday landscape into something
01:40
ethereal and otherworldly,
01:42
and this happens around the globe,
01:44
like this hillside in the Smoky Mountains
01:46
that I saw transformed into a living cascade of light
01:48
by the eerie glows of these blue ghost fireflies,
01:52
or a roadside river that I visited in Japan
01:56
as it was giving birth to the slow, floating flashes
01:59
of these Genji fireflies,
02:03
or in Malaysia, the mangrove trees
02:06
that I watched blossom nightly
02:09
not with flowers
02:11
but with the lights of a thousand —
(Bleep! Bleep!) — fireflies,
02:12
all blinking together
02:15
in stunning synchrony.
02:17
These luminous landscapes
02:20
still fill me with wonder,
02:22
and they keep me connected to the magic
02:24
of the natural world.
02:27
And I find it amazing that they're created
02:29
by these tiny insects.
02:31
In person, fireflies are charming.
02:34
They're charismatic.
02:37
They've been celebrated in art
02:39
and in poetry for centuries.
02:40
As I've traveled around the world,
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I've met many thoughtful people
02:44
who have told me that God put fireflies on Earth
02:46
for humans to enjoy.
02:49
Other creatures can enjoy them too.
02:51
I think these graceful insects are truly miraculous
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because they so beautifully illuminate
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the creative improvisation of evolution.
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They've been shaped by two powerful
03:06
evolutionary forces:
03:08
natural selection, the struggle for survival,
03:10
and sexual selection,
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the struggle for reproductive opportunity.
03:15
As a firefly junkie, the past 20 years
03:19
have been quite an exciting ride.
03:22
Together with my students at Tufts University
03:24
and other colleagues,
03:27
we've made lots of new discoveries about fireflies:
03:28
their courtship and sex lives,
03:31
their treachery and murder.
03:33
So today I'd like to share with you
03:36
just a couple of tales that we've brought back
03:38
from our collective adventures
03:41
into this hidden world.
03:43
Fireflies belong to a very beautiful
03:47
and diverse group of insects, the beetles.
03:50
Worldwide, there are more than 2,000 firefly species,
03:54
and these have evolved remarkably diverse
03:59
courtship signals,
04:01
that is, different ways to find and attract mates.
04:02
Around 150 million years ago,
04:06
the very first fireflies probably looked like this.
04:08
They flew during the daytime
04:11
and they didn't light up.
04:13
Instead, males used their fantastic antennae
04:15
to sniff out perfumes given off by their females.
04:18
In other fireflies, it's only the females who light up.
04:22
They are attractively plump and wingless,
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so every night, they climb up onto perches
04:30
and they glow brightly for hours
04:32
to attract their flying but unlit males.
04:34
In still other fireflies, both sexes
04:39
use quick, bright flashes to find their mates.
04:41
Here in North America,
04:45
we have more than 100 different kinds of firefly
04:46
that have the remarkable ability to shine energy
04:49
out from their bodies
04:53
in the form of light.
04:55
How do they do that?
04:57
It seems totally magical,
05:00
but these bioluminescent signals
05:02
arise from carefully orchestrated chemical reactions
05:03
that happen inside the firefly lantern.
05:06
The main star is an enzyme called luciferase,
05:09
which in the course of evolution
05:13
has figured out a way to wrap its tiny arms
05:14
around an even smaller molecule called luciferin,
05:18
in the process getting it so excited
05:21
that it actually gives off light.
05:24
Incredible.
05:27
But how could these bright lights
05:29
have benefited some proto-firefly?
05:31
To answer this question, we need to flip back
05:35
in the family album to some baby pictures.
05:37
Fireflies completely reinvent
their bodies as they grow.
05:41
They spend the vast majority of their lifetime,
05:45
up to two years,
05:47
in this larval form.
05:49
Their main goal here, like my teenagers,
05:52
is to eat and grow.
05:54
And firefly light first originated
05:57
in these juveniles.
06:00
Every single firefly larva can light up,
06:02
even when their adults can't.
06:04
But what's the point
06:07
to being so conspicuous?
06:08
Well, we know that these juveniles
06:12
make nasty-tasting chemicals
06:13
that help them survive their extended childhood,
06:15
so we think these lights first evolved as a warning,
06:19
a neon sign that says, "Toxic! Stay away!"
06:23
to any would-be predators.
06:27
It took many millions of years
06:30
before these bright lights
06:33
evolved into a smart communication tool
06:35
that could be used not just to
ward off potential predators
06:37
but to bring in potential mates.
06:40
Driven now by sexual selection,
06:43
some adult fireflies
06:46
like this proud male
06:48
evolved a shiny new glow-in-the-dark lantern
06:50
that would let them take courtship
06:54
to a whole new level.
06:56
These adults only live a few weeks,
07:00
and now they're single-mindedly focused on sex,
07:02
that is, on propelling their genes
07:07
into the next firefly generation.
07:09
So we can follow this male out into the field
07:12
as he joins hundreds of other males
07:15
who are all showing off their new courtship signals.
07:18
It's amazing to think that the luminous displays
07:22
we admire
07:25
here and in fact everywhere around the world
07:27
are actually the silent love songs
07:30
of male fireflies.
07:34
They're flying and flashing their hearts out.
07:37
I still find it very romantic.
07:41
But meanwhile, where are all the females?
07:44
Well, they're lounging down below
07:48
surveying their options.
07:49
They have plenty of males to choose from,
07:51
and these females turn out to be very picky.
07:53
When a female sees a flash
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from an especially attractive male,
08:00
she'll aim her lantern in his direction,
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and give him a flash back.
08:05
It's her "come hither" sign.
08:08
So he flies closer and he flashes again.
08:11
If she still likes him,
08:15
they'll strike up a conversation.
08:16
These creatures speak their love
08:19
in the language of light.
08:22
So what exactly do these females consider sexy?
08:25
We decided to conduct some firefly opinion polls
08:30
to find out.
08:32
When we tested females using blinking LED lights,
08:34
we discovered they prefer males
08:37
who give longer-lasting flashes.
08:40
(Laughter) (Applause)
08:44
I know you're wondering,
08:47
what gives these males their sex appeal?
08:48
Now we get to see what happens
08:52
when the lights go out.
08:53
The first thing we discovered
08:56
is that once a male and female hook up like this,
08:57
they stay together all night long,
09:00
and when we looked inside
09:03
to see what might be happening,
09:04
we discovered a surprising new twist
09:05
to firefly sex.
09:07
While they're mating,
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the male is busy giving the female
09:11
not just his sperm
09:12
but also a nutrient-filled package
09:14
called a nuptial gift.
09:18
We can zoom in to look more closely
09:23
inside this mating pair.
09:25
We can actually see the gift —
09:27
it's shown here in red —
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as it's being passed from the male to the female.
09:30
What makes this gift so valuable
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is that it's packed with protein
09:37
that the female will use to provision her eggs.
09:39
So females are keeping their eyes on this prize
09:43
as they size up potential mates.
09:47
We discovered that females use male flash signals
09:49
to try to predict which males
09:52
have the biggest gifts to offer,
09:54
because this bling helps the female lay more eggs
09:56
and ultimately launch more of her own offspring
10:01
into the next generation.
10:04
So it's not all sweetness and light.
10:09
Firefly romance is risky.
10:11
For the most part, these adult fireflies
10:14
don't get eaten because like their juveniles
10:16
they can manufacture toxins that are repellent
10:19
to birds and other insectivores,
10:22
but somewhere along the line,
10:25
one particular group of fireflies
10:27
somehow lost the metabolic machinery
10:30
needed to make their own protective toxins.
10:33
This evolutionary flaw,
10:37
which was discovered by my colleague Tom Eisner,
10:39
has driven these fireflies
10:42
to take their bright lights out into the night
10:44
with treacherous intent.
10:47
Dubbed "femme fatales"
10:51
by Jim Lloyd, another colleague,
10:52
these females have figured out how to target
10:55
the males of other firefly species.
10:58
So the hunt begins with the predator —
11:02
she's shown here in the lower left —
11:03
where she's sitting quietly
11:05
and eavesdropping on the courtship conversation
11:08
of her intended prey,
11:11
and here's how it might go.
11:12
First the prey male flashes, "Do you love me?"
11:14
His own female responds, "Maybe."
11:18
So then he flashes again.
11:22
But this time, the predator sneaks in a reply
11:25
that cleverly mimics exactly
what the other female just said.
11:28
She's not looking for love: she's looking for toxins.
11:34
If she's good, she can lure this male close enough
11:39
to reach out and grab him,
11:43
and he's not just a light snack.
11:45
Over the next hour, she slowly
11:48
exsanguinates this male
11:51
leaving behind just some gory remains.
11:54
Unable to make their own toxins,
11:57
these females resort to drinking the blood
12:00
of other fireflies to get these protective chemicals.
12:02
So a firefly vampire,
12:07
brought to you by natural selection.
12:13
We still have a lot to learn about fireflies,
12:17
but it looks like many stories will remain untold,
12:20
because around the world, firefly populations
12:24
are blinking out.
12:26
The main culprit: habitat loss.
12:29
Pretty much everywhere, the fields and forests,
12:32
the mangroves and meadows
that fireflies need to survive,
12:34
are giving way to development and to sprawl.
12:37
Here's another problem: we've conquered darkness,
12:41
but in the process, we spill so
much extra light out into the night
12:45
that it disrupts the lives of other creatures,
12:48
and fireflies are especially sensitive to light pollution
12:51
because it obscures the signals
12:55
that they use to find their mates.
12:57
Do we really need fireflies?
13:02
After all, they're just one tiny bit
13:04
of Earth's biodiversity.
13:06
Yet every time a species is lost,
13:08
it's like extinguishing a room full of candles
13:12
one by one.
13:14
You might not notice
13:17
when the first few flames flicker out,
13:18
but in the end, you're left sitting in darkness.
13:21
As we work together to craft a planetary future,
13:31
I hope we can find a way
13:36
to keep these bright lights shining.
13:38
Thank you.
13:42
(Applause)
13:44

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Sara Lewis - Firefly specialist
Evolutionary ecologist Sara Lewis digs deep into firefly mating rituals to uncover a world of secret languages and strange gifts in these silent sparks.

Why you should listen
Before Sara Lewis lifted the lid on the unexplored lives of fireflies, much of the sexual intrigue behind their flashing displays was a mystery. Although initially focused on sea creatures, Lewis became hooked on these enigmatic insects, realizing that when it came to firefly mating habits, "we had no idea what went on once the lights went out," as she told the New York Times.

Her fascination has led Lewis, a professor at Tufts University, to pursue field and laboratory studies of fireflies around the world. In the course of her groundbreaking research, she’s illuminated many surprising twists of firefly behavior: including elaborate flash dances, predatory eavesdropping and deceit, and “wedding gift” delivery services (video).
The original video is available on TED.com
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