FEMALE NARRATOR: We like to think we're in control, that our minds are our own, but that's not true for this fruit fly.

Its brain has been hijacked by another organism, and it's not going to end well.

It all starts when the fly is innocently walking around, sipping on overripe fruit.

It picks up an invisible fungus spore which bores under its skin.

For a few days, everything seems normal, but inside, the fungus is growing, feeding on the fly's fat, and infiltrating its mind.

At dusk on the fourth or fifth day, the fly gets a little erratic, wandering around.

It climbs to a high place.

Scientists call this behavior summiting.

Then it starts twitching.

The fungus is in control.

The fly sticks out its mouth part and spits out a tiny drop of sticky liquid.

That glues the fly down, sealing its fate.

A few minutes later, its wings shoot up, and it dies.

Now that the fungus has forced the fly into this death pose, wings out of the way, nothing can stop it.

It emerges.

Tiny spore launchers burst out on the fly's skin.

Hundreds of spores shoot out at high speed, catching a breeze if the fly climbed high enough.

They're the next generation of killer fungus.

It continues for hours, spores flying out.

These fires are in the wrong place at the wrong time, and if spores land on a wing, which they can't bore into, they shoot out a secondary spore to increase their chances of spreading.

So how does a fungus take control of a brain?

At Harvard, Carolyn Elia is trying to understand that.

She thinks the fungus secretes chemicals to manipulate the fly's neurons, maybe stimulating the ones that make flies climb.

But don't worry.

The fungus can't hurt humans.

Scientists have tried to harness its power for our benefit to kill flies in our kitchens and farms.

They haven't had any luck, though.

The deadly spores are actually pretty fragile and short-lived.

It turns out this lethal puppet master does only what it needs to for its own survival.

Hi, it's Lauren again.

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