The loves and lies of fireflies

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.

As a scientist, and also as a human being,

I've been trying to make myself

susceptible to wonder.

I think Jason Webley last night called it

"conspiring to be part of the magic."

So it's fortunate that my career as a biologist

lets me dive deeply into the lives

of some truly wondrous creatures

that share our planet:

fireflies.

Now, for many of you, I know that fireflies

might conjure up some really great memories:

childhood, summertime,

even other TED Talks.

Maybe something like this.

My seduction into the world of fireflies

began when I was back in graduate school.

One evening, I was sitting out in my backyard

in North Carolina,

and suddenly, these silent sparks

rose up all around me,

and I began to wonder:

How do these creatures make light,

and what's with all this flashing?

Are they talking to one another?

And what happens after the lights go out?

I've been lucky enough to answer

some of these questions

as I've explored this nocturnal world.

Now if you've ever seen

or even heard about fireflies,

then you'll know how magically they can transform

our everyday landscape into something

ethereal and otherworldly,

and this happens around the globe,

like this hillside in the Smoky Mountains

that I saw transformed into a living cascade of light

by the eerie glows of these blue ghost fireflies,

or a roadside river that I visited in Japan

as it was giving birth to the slow, floating flashes

of these Genji fireflies,

or in Malaysia, the mangrove trees

that I watched blossom nightly

not with flowers

but with the lights of a thousand —
(Bleep! Bleep!) — fireflies,

all blinking together

in stunning synchrony.

These luminous landscapes

still fill me with wonder,

and they keep me connected to the magic

of the natural world.

And I find it amazing that they're created

by these tiny insects.

In person, fireflies are charming.

They're charismatic.

They've been celebrated in art

and in poetry for centuries.

As I've traveled around the world,

I've met many thoughtful people

who have told me that God put fireflies on Earth

for humans to enjoy.

Other creatures can enjoy them too.

I think these graceful insects are truly miraculous

because they so beautifully illuminate

the creative improvisation of evolution.

They've been shaped by two powerful

evolutionary forces:

natural selection, the struggle for survival,

and sexual selection,

the struggle for reproductive opportunity.

As a firefly junkie, the past 20 years

have been quite an exciting ride.

Together with my students at Tufts University

and other colleagues,

we've made lots of new discoveries about fireflies:

their courtship and sex lives,

their treachery and murder.

So today I'd like to share with you

just a couple of tales that we've brought back

from our collective adventures

into this hidden world.

Fireflies belong to a very beautiful

and diverse group of insects, the beetles.

Worldwide, there are more than 2,000 firefly species,

and these have evolved remarkably diverse

courtship signals,

that is, different ways to find and attract mates.

Around 150 million years ago,

the very first fireflies probably looked like this.

They flew during the daytime

and they didn't light up.

Instead, males used their fantastic antennae

to sniff out perfumes given off by their females.

In other fireflies, it's only the females who light up.

They are attractively plump and wingless,

so every night, they climb up onto perches

and they glow brightly for hours

to attract their flying but unlit males.

In still other fireflies, both sexes

use quick, bright flashes to find their mates.

Here in North America,

we have more than 100 different kinds of firefly

that have the remarkable ability to shine energy

out from their bodies

in the form of light.

How do they do that?

It seems totally magical,

but these bioluminescent signals

arise from carefully orchestrated chemical reactions

that happen inside the firefly lantern.

The main star is an enzyme called luciferase,

which in the course of evolution

has figured out a way to wrap its tiny arms

around an even smaller molecule called luciferin,

in the process getting it so excited

that it actually gives off light.

Incredible.

But how could these bright lights

have benefited some proto-firefly?

To answer this question, we need to flip back

in the family album to some baby pictures.

Fireflies completely reinvent
their bodies as they grow.

They spend the vast majority of their lifetime,

up to two years,

in this larval form.

Their main goal here, like my teenagers,

is to eat and grow.

And firefly light first originated

in these juveniles.

Every single firefly larva can light up,

even when their adults can't.

But what's the point

to being so conspicuous?

Well, we know that these juveniles

make nasty-tasting chemicals

that help them survive their extended childhood,

so we think these lights first evolved as a warning,

a neon sign that says, "Toxic! Stay away!"

to any would-be predators.

It took many millions of years

before these bright lights

evolved into a smart communication tool

that could be used not just to
ward off potential predators

but to bring in potential mates.

Driven now by sexual selection,

some adult fireflies

like this proud male

evolved a shiny new glow-in-the-dark lantern

that would let them take courtship

to a whole new level.

These adults only live a few weeks,

and now they're single-mindedly focused on sex,

that is, on propelling their genes

into the next firefly generation.

So we can follow this male out into the field

as he joins hundreds of other males

who are all showing off their new courtship signals.

It's amazing to think that the luminous displays

we admire

here and in fact everywhere around the world

are actually the silent love songs

of male fireflies.

They're flying and flashing their hearts out.

I still find it very romantic.

But meanwhile, where are all the females?

Well, they're lounging down below

surveying their options.

They have plenty of males to choose from,

and these females turn out to be very picky.

When a female sees a flash

from an especially attractive male,

she'll aim her lantern in his direction,

and give him a flash back.

It's her "come hither" sign.

So he flies closer and he flashes again.

If she still likes him,

they'll strike up a conversation.

These creatures speak their love

in the language of light.

So what exactly do these females consider sexy?

We decided to conduct some firefly opinion polls

to find out.

When we tested females using blinking LED lights,

we discovered they prefer males

who give longer-lasting flashes.

(Laughter) (Applause)

I know you're wondering,

what gives these males their sex appeal?

Now we get to see what happens

when the lights go out.

The first thing we discovered

is that once a male and female hook up like this,

they stay together all night long,

and when we looked inside

to see what might be happening,

we discovered a surprising new twist

to firefly sex.

While they're mating,

the male is busy giving the female

not just his sperm

but also a nutrient-filled package

called a nuptial gift.

We can zoom in to look more closely

inside this mating pair.

We can actually see the gift —

it's shown here in red —

as it's being passed from the male to the female.

What makes this gift so valuable

is that it's packed with protein

that the female will use to provision her eggs.

So females are keeping their eyes on this prize

as they size up potential mates.

We discovered that females use male flash signals

to try to predict which males

have the biggest gifts to offer,

because this bling helps the female lay more eggs

and ultimately launch more of her own offspring

into the next generation.

So it's not all sweetness and light.

Firefly romance is risky.

For the most part, these adult fireflies

don't get eaten because like their juveniles

they can manufacture toxins that are repellent

to birds and other insectivores,

but somewhere along the line,

one particular group of fireflies

somehow lost the metabolic machinery

needed to make their own protective toxins.

This evolutionary flaw,

which was discovered by my colleague Tom Eisner,

has driven these fireflies

to take their bright lights out into the night

with treacherous intent.

Dubbed "femme fatales"

by Jim Lloyd, another colleague,

these females have figured out how to target

the males of other firefly species.

So the hunt begins with the predator —

she's shown here in the lower left —

where she's sitting quietly

and eavesdropping on the courtship conversation

of her intended prey,

and here's how it might go.

First the prey male flashes, "Do you love me?"

His own female responds, "Maybe."

So then he flashes again.

But this time, the predator sneaks in a reply

that cleverly mimics exactly
what the other female just said.

She's not looking for love: she's looking for toxins.

If she's good, she can lure this male close enough

to reach out and grab him,

and he's not just a light snack.

Over the next hour, she slowly

exsanguinates this male

leaving behind just some gory remains.

Unable to make their own toxins,

these females resort to drinking the blood

of other fireflies to get these protective chemicals.

So a firefly vampire,

brought to you by natural selection.

We still have a lot to learn about fireflies,

but it looks like many stories will remain untold,

because around the world, firefly populations

are blinking out.

The main culprit: habitat loss.

Pretty much everywhere, the fields and forests,

the mangroves and meadows
that fireflies need to survive,

are giving way to development and to sprawl.

Here's another problem: we've conquered darkness,

but in the process, we spill so
much extra light out into the night

that it disrupts the lives of other creatures,

and fireflies are especially sensitive to light pollution

because it obscures the signals

that they use to find their mates.

Do we really need fireflies?

After all, they're just one tiny bit

of Earth's biodiversity.

Yet every time a species is lost,

it's like extinguishing a room full of candles

one by one.

You might not notice

when the first few flames flicker out,

but in the end, you're left sitting in darkness.

As we work together to craft a planetary future,

I hope we can find a way

to keep these bright lights shining.

Thank you.

(Applause)