WEBVTT

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As a scientist, and also as a human being,

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I've been trying to make myself

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susceptible to wonder.

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I think Jason Webley last night called it

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"conspiring to be part of the magic."

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So it's fortunate that my career as a biologist

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lets me dive deeply into the lives

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of some truly wondrous creatures

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that share our planet:

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fireflies.

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Now, for many of you, I know that fireflies

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might conjure up some really great memories:

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childhood, summertime,

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even other TED Talks.

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Maybe something like this.

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My seduction into the world of fireflies

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began when I was back in graduate school.

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One evening, I was sitting out in my backyard

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in North Carolina,

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and suddenly, these silent sparks

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rose up all around me,

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and I began to wonder:

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How do these creatures make light,

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and what's with all this flashing?

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Are they talking to one another?

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And what happens after the lights go out?

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I've been lucky enough to answer

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some of these questions

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as I've explored this nocturnal world.

NOTE Paragraph

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Now if you've ever seen

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or even heard about fireflies,

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then you'll know how magically they can transform

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our everyday landscape into something

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ethereal and otherworldly,

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and this happens around the globe,

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like this hillside in the Smoky Mountains

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that I saw transformed into a living cascade of light

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by the eerie glows of these blue ghost fireflies,

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or a roadside river that I visited in Japan

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as it was giving birth to the slow, floating flashes

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of these Genji fireflies,

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or in Malaysia, the mangrove trees

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that I watched blossom nightly

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not with flowers

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

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all blinking together

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in stunning synchrony.

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These luminous landscapes

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still fill me with wonder,

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and they keep me connected to the magic

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of the natural world.

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And I find it amazing that they're created

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by these tiny insects.

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In person, fireflies are charming.

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They're charismatic.

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They've been celebrated in art

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and in poetry for centuries.

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As I've traveled around the world,

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I've met many thoughtful people

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who have told me that God put fireflies on Earth

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for humans to enjoy.

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Other creatures can enjoy them too.

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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

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evolutionary forces:

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natural selection, the struggle for survival,

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and sexual selection,

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the struggle for reproductive opportunity.

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As a firefly junkie, the past 20 years

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have been quite an exciting ride.

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Together with my students at Tufts University

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and other colleagues,

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we've made lots of new discoveries about fireflies:

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their courtship and sex lives,

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their treachery and murder.

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So today I'd like to share with you

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just a couple of tales that we've brought back

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from our collective adventures

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into this hidden world.

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Fireflies belong to a very beautiful

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and diverse group of insects, the beetles.

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

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and these have evolved remarkably diverse

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courtship signals,

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that is, different ways to find and attract mates.

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Around 150 million years ago,

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the very first fireflies probably looked like this.

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They flew during the daytime

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and they didn't light up.

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Instead, males used their fantastic antennae

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to sniff out perfumes given off by their females.

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

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They are attractively plump and wingless,

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so every night, they climb up onto perches

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and they glow brightly for hours

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to attract their flying but unlit males.

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In still other fireflies, both sexes

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use quick, bright flashes to find their mates.

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Here in North America,

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we have more than 100 different kinds of firefly

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that have the remarkable ability to shine energy

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out from their bodies

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in the form of light.

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How do they do that?

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It seems totally magical,

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but these bioluminescent signals

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arise from carefully orchestrated chemical reactions

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that happen inside the firefly lantern.

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The main star is an enzyme called luciferase,

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which in the course of evolution

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has figured out a way to wrap its tiny arms

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around an even smaller molecule called luciferin,

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in the process getting it so excited

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that it actually gives off light.

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Incredible.

NOTE Paragraph

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But how could these bright lights

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have benefited some proto-firefly?

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To answer this question, we need to flip back

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in the family album to some baby pictures.

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Fireflies completely reinvent
their bodies as they grow.

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They spend the vast majority of their lifetime,

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up to two years,

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in this larval form.

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Their main goal here, like my teenagers,

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is to eat and grow.

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And firefly light first originated

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in these juveniles.

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Every single firefly larva can light up,

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even when their adults can't.

NOTE Paragraph

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But what's the point

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to being so conspicuous?

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Well, we know that these juveniles

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make nasty-tasting chemicals

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that help them survive their extended childhood,

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so we think these lights first evolved as a warning,

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

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to any would-be predators.

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It took many millions of years

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before these bright lights

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evolved into a smart communication tool

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that could be used not just to
ward off potential predators

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but to bring in potential mates.

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Driven now by sexual selection,

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some adult fireflies

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like this proud male

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

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that would let them take courtship

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to a whole new level.

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These adults only live a few weeks,

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

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that is, on propelling their genes

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into the next firefly generation.

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So we can follow this male out into the field

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as he joins hundreds of other males

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who are all showing off their new courtship signals.

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It's amazing to think that the luminous displays

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we admire

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here and in fact everywhere around the world

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are actually the silent love songs

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of male fireflies.

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They're flying and flashing their hearts out.

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I still find it very romantic.

NOTE Paragraph

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But meanwhile, where are all the females?

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Well, they're lounging down below

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surveying their options.

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They have plenty of males to choose from,

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and these females turn out to be very picky.

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When a female sees a flash

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from an especially attractive male,

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she'll aim her lantern in his direction,

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and give him a flash back.

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It's her "come hither" sign.

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So he flies closer and he flashes again.

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If she still likes him,

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they'll strike up a conversation.

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These creatures speak their love

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in the language of light.

NOTE Paragraph

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So what exactly do these females consider sexy?

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We decided to conduct some firefly opinion polls

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to find out.

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When we tested females using blinking LED lights,

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we discovered they prefer males

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who give longer-lasting flashes.

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(Laughter) (Applause)

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I know you're wondering,

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what gives these males their sex appeal?

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Now we get to see what happens

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when the lights go out.

NOTE Paragraph

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The first thing we discovered

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

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they stay together all night long,

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and when we looked inside

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to see what might be happening,

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we discovered a surprising new twist

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to firefly sex.

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While they're mating,

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the male is busy giving the female

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not just his sperm

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but also a nutrient-filled package

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called a nuptial gift.

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We can zoom in to look more closely

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inside this mating pair.

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We can actually see the gift —

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it's shown here in red —

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

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What makes this gift so valuable

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is that it's packed with protein

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that the female will use to provision her eggs.

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So females are keeping their eyes on this prize

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as they size up potential mates.

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We discovered that females use male flash signals

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to try to predict which males

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have the biggest gifts to offer,

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because this bling helps the female lay more eggs

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and ultimately launch more of her own offspring

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into the next generation.

NOTE Paragraph

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So it's not all sweetness and light.

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Firefly romance is risky.

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For the most part, these adult fireflies

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don't get eaten because like their juveniles

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they can manufacture toxins that are repellent

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to birds and other insectivores,

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but somewhere along the line,

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one particular group of fireflies

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somehow lost the metabolic machinery

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needed to make their own protective toxins.

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This evolutionary flaw,

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which was discovered by my colleague Tom Eisner,

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has driven these fireflies

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to take their bright lights out into the night

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with treacherous intent.

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Dubbed "femme fatales"

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by Jim Lloyd, another colleague,

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these females have figured out how to target

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the males of other firefly species.

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So the hunt begins with the predator —

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she's shown here in the lower left —

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where she's sitting quietly

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and eavesdropping on the courtship conversation

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of her intended prey,

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and here's how it might go.

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

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His own female responds, "Maybe."

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So then he flashes again.

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But this time, the predator sneaks in a reply

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that cleverly mimics exactly
what the other female just said.

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

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

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to reach out and grab him,

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and he's not just a light snack.

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Over the next hour, she slowly

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exsanguinates this male

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leaving behind just some gory remains.

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Unable to make their own toxins,

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these females resort to drinking the blood

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of other fireflies to get these protective chemicals.

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So a firefly vampire,

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brought to you by natural selection.

NOTE Paragraph

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We still have a lot to learn about fireflies,

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but it looks like many stories will remain untold,

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because around the world, firefly populations

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are blinking out.

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The main culprit: habitat loss.

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Pretty much everywhere, the fields and forests,

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the mangroves and meadows
that fireflies need to survive,

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are giving way to development and to sprawl.

NOTE Paragraph

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

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

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that it disrupts the lives of other creatures,

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and fireflies are especially sensitive to light pollution

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because it obscures the signals

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that they use to find their mates.

NOTE Paragraph

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Do we really need fireflies?

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After all, they're just one tiny bit

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of Earth's biodiversity.

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Yet every time a species is lost,

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it's like extinguishing a room full of candles

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one by one.

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You might not notice

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when the first few flames flicker out,

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

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As we work together to craft a planetary future,

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I hope we can find a way

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to keep these bright lights shining.

NOTE Paragraph

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Thank you.

NOTE Paragraph

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(Applause)