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I would like to introduce you to my favorite parasite.

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There are millions that I could choose from

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and this is it:

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it's called the jewel wasp.

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You can find it in parts of Africa and Asia.

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It's a little under an inch long,

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and it is a beautiful looking parasite.

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Now, you may be saying to yourself,

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"This is not a parasite.

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It's not a tapeworm,

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it's not a virus,

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how could a wasp be a parasite?"

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You are probably thinking about regular wasps,

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you know, the ones that build paper nests as their house.

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Well, the thing is that the jewel wasp

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makes its house inside a living cockroach.

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Here's how it happens.

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A jewel wasp is flying around, looking for a cockroach.

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When it sees one, it lands and bites on its wing.

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So, I'll be the cockroach.

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Be-wha! Bewha!

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And the cockroach starts shaking it off,

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"Get away from me!"

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The wasp very quickly starts stinging the cockroach.

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All of a sudden, the cockroach can't move,

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for about a minute.

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And then it recovers

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and stands up.

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It could run away now,

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but it doesn't.

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It just doesn't want to.

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It just stays there.

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It's become a zombie slave.

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Again, I'm not making this up.

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The wasp goes off,

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it walks away and finds a hole

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and digs it out, makes it into a burrow.

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It walks back.

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This can take up to half an hour.

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The cockroach is still there.

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What do we do now?

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The wasps grabs onto one of the antenna,

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bites down on it,

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of the cockroach,

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and pulls the cockroach.

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And the cockroach says, "Alright,"

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and walks like a dog on a leash.

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The wasp takes it all the way down into the burrow.

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The cockroach says, "Nice place."

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The wasp takes care of some business

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and then goes and leaves the burrow

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and seals it shut,

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leaving the cockroach entombed in darkness, still alive.

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The cockroach says, "Alright, I'll stay here if you want."

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Now, I mentioned that the cockroach took care,

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ah, the wasp took care of a little business

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before it left the burrow.

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The business was laying an egg

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on the underside of the cockroach.

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The egg hatches.

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Out comes a wasp larva.

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It looks kind of like a maggot with big, nasty jaws.

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It chews a hole into the cockroach

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and starts to feed from the outside.

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It gets bigger, like you can see over here.

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And then when it gets big enough,

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it decides to crawl into the hole,

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into the cockroach.

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So now it's inside the still-living cockroach

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and the cockroach doesn't mind much.

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This goes on for about a month.

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The larva grows and grows and grows,

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then makes a pupa, kind of like a cocoon.

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Inside there it grows eyes,

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it grows wings,

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it grows legs,

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the cockroach is still alive, still waiting.

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Finally the wasp is ready to leave,

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and that's when the cockroach finally dies

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because the fullly-formed adult wasp

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crawls out of the cockroach's dying body.

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The wasp shakes itself off,

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climbs out of the burrow,

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goes and finds another wasp to mate with

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to start this whole, crazy cycle again.

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So, this is not science fiction,

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this happens every day, all over the world.

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And scientists are totally fascinated by this.

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They're just starting to figure out how all this happens.

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And, when you really start to look at the science of it,

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you start to kind of respect this very creepy wasp.

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You see, the thing is that when it attacks the cockroach,

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it's not just stinging wildly,

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it delivers two precise stings.

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It knows this cockroach's nervous system

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like you know the back of your hand.

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The first sting goes to that spot there,

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called the "walking rhythm generators,"

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and, as you can guess,

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those are the neurons that send signals

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to the legs to move.

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It blocks the channels that the neurons use

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to send these signals.

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So the cockroach wants to go, it wants to run away,

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but it can't because it can't move its legs.

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And that lasted for about a minute.

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This is really sophisticated pharmacology.

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We actually use the same method,

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a drug called Ivermectin,

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to cure river blindness,

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which is called by a parasitic worm

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that gets into your eye.

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If you take Ivermectin, you paralyze the worm

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using the same strategy.

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Now, we discovered this in the 1970s,

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the wasp has been doing this for millions of years.

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Then comes the second sting.

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Now the second sting actually hits two places along the way.

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And to try to imagine how this can happen,

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I want you to picture yourself with a friend

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who's got a very long, very, very scary looking needle.

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And your friend,

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or at least you thought he was your friend,

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sticks it in your neck,

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goes into your skull,

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stops off at one part of your brain

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and injects some drugs,

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then keeps going in your brain

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and injects some more.

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These are two particular spots,

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marked here, "SEG",

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and you can see the tip of it in the brain, marked "Br".

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Now, we can do this, but it's really hard for us.

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It's called stereotactic drug delivery.

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You have to put a patient in a big metal frame

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to hold them still,

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you need CAT Scans to know where you're going,

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so you look at the picture and say,

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"Are we going the right way?"

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The jewel wasp has sensors on its stinger

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and scientists think that it can actually feel its way

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through the cockroach's brain until it gets

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to the exact, right place,

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and then penetrates an individual neuron

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and then delivers the goods.

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So, this is quite amazing stuff,

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and what seems to happen then

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is that the wasp is taking away the control

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that the cockroach has over its own body.

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It's taking away the cockroach's free will.

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We didn't really appreciate that cockroaches

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have free will until this wasp showed us.

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And, we have no idea how it's doing this,

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we don't know yet what the venom has in it

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and we don't know which circuits

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it's hitting in the cockroach's brain,

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and I think that's why this is,

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most of all, my favorite parasite

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because we have so much left to learn from it.

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Thank you very much.