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Greg Gage: If I asked you
to think of a ferocious killer animal,

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you'd probably think of a lion,

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and for all the wonderful
predatory skills that a lion has,

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it still only has about a 20 percent
success rate at catching a meal.

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Now, one of the most successful hunters

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in the entire animal kingdom
is surprising:

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the dragonfly.

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Now, dragonflies are killer flies,

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and when they see a smaller fly,

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they have about a 97 percent
chance of catching it for a meal.

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And this is in mid-flight.

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But how can such
a small insect be so precise?

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In this episode, we're going to see

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how the dragonfly's brain is highly
specialized to be a deadly killer.

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[DIY Neuroscience]

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So what makes the dragonfly
one of the most successful predators

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in the animal kingdom?

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One, it's the eyes.

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It has near 360-degree vision.

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Two, the wings.

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With individual control of its wings,

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the dragonfly can move
precisely in any direction.

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But the real secret
to the dragonfly's success

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is how its brain coordinates
this complex information

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between the eyes and the wings

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and turns hunting into a simple reflex.

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To study this, Jaimie's been
spending a lot of time

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socializing with dragonflies.

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What do you need to do your experiments?

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Jaimie Spahr: First of all,
you need dragonflies.

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Oliver: I have a mesh cage
to catch the dragonflies.

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JS: The more I worked with them,
the more terrified I got of them.

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They're actually very scary,
especially under a microscope.

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They have really sharp mandibles,
are generally pretty aggressive,

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which I guess also helps them
to be really good predators.

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GG: In order to learn what's going on
inside the dragonfly's brain

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when it sees a prey,

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we're going to eavesdrop in
on a conversation

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between the eyes and the wings,

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and to do that, we need
to anesthetize the dragonfly on ice

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and make sure we protect its wings
so that we can release it afterwards.

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Now, the dragonfly's brain is made up
of specialized cells called neurons

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and these neurons
are what allow the dragonfly

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to see and move so quickly.

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The individual neurons form circuits
by connecting to each other

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via long, tiny threads called axons

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and the neurons communicate
over these axons using electricity.

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In the dragonfly, we're going to place
little metal wires, or electrodes,

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along the axon tracks,

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and this is what's really cool.

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In the dragonfly, there's only 16 neurons;

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that's eight per eye

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that tell the wings
exactly where the target is.

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We've placed the electrodes
so that we can record from these neurons

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that connect the eyes to the wings.

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Whenever a message is being passed
from the eye to the wing,

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our electrode intercepts that conversation
in the form of an electrical current,

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and it amplifies it.

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Now, we can both hear it and see it
in the form of a spike,

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which we also call an action potential.

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Now let's listen in.

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Right now, we have the dragonfly
flipped upside down,

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so he's looking down towards the ground.

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We're going to take a prey,
or what we sometimes call a target.

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In this case, the target's
going to be a fake fly.

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We're going to move it
into the dragonfly's sights.

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(Buzzing)

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Oh!

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Oh, look at that.

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Look at that, but it's only
in one direction.

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Oh, yes!

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You don't see any spikes
when I go forward,

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but they're all when I come back.

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In our experiments,

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we were able to see
that the neurons of the dragonfly

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fired when we moved the target
in one direction but not the other.

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Now, why is that?

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Remember when I said that the dragonfly

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had near 360-degree vision.

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Well, there's a section
of the eye called the fovea

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and this is the part
that has the sharpest visual acuity,

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and you can think of it as its crosshairs.

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Remember when I told you the dragonfly had
individual precise control of its wings?

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When a dragonfly sees its prey,
it trains its crosshairs on it

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and along its axons
it sends messages only to the neurons

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that control the parts of the wings

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that are needed
to keep that dragonfly on target.

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So if the prey is
on the left of the dragonfly,

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only the neurons that are tugging
the wings to the left are fired.

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And if the prey moves
to the right of the dragonfly,

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those same neurons are not needed,
so they're going to remain quiet.

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And the dragonfly speeds toward the prey

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at a fixed angle that's communicated
by this crosshairs to the wings,

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and then boom, dinner.

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Now, all this happens in a split second,
and it's effortless for the dragonfly.

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It's almost like a reflex.

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And this whole incredibly efficient
process is called fixation.

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But there's one more
story to this process.

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We saw how the neurons
respond to movements,

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but how does the dragonfly know
that something really is prey?

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This is where size matters.

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Let's show the dragonfly a series of dots.

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Oh, yeah!

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JS: Yeah, it prefers that one.

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GG: Out of all the sizes,

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we found that the dragonfly responded
to smaller targets over larger ones.

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In other words, the dragonfly
was programmed to go after smaller flies

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versus something much larger, like a bird.

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And as soon as it recognizes
something as prey,

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that poor little fly
only has seconds to live.

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Today we got to see
how the dragonfly's brain works

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to make it a very efficient killer.

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And let's be thankful
that we didn't live 300 million years ago

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when dragonflies were the size of cats.