[MUSIC PLAYING] NARRATOR: We mammals like to think we're pretty special, right?

We don't lay eggs.

We feed our babies milk.

Well, this very pregnant fly is about to prove us wrong.

Yep, this tsetse fly is in labor.

And that emerging bundle of joy is her larvae.

While other insects can lay hundreds of eggs, she grows one baby at a time inside her, just like us.

Congratulations?

Scientists think tsetse flies started growing their young like this long ago to guard them from parasites.

For that same reason, the larva doesn't stick around.

It burrows into the dirt for protection.

It's already gotten all the nutrition it needs from its mom's milk.

That's right-- this fly makes milk.

Here's a drop of it under the microscope.

It's made up of protein and fat, a lot like breast milk.

The fly doesn't exactly breastfeed, though.

Inside its mom, the larva got milk through these tubes, which it drank with this pair of strawlike mouth parts on its head.

A female tsetse fly needs a lot of fuel because over her ten-day pregnancy, she produces her own body weight in milk.

And that fuel comes from us.

Tsetses feed exclusively on blood-- from humans and other animals.

That's bad news, because where the flies live in Africa, they spread a debilitating disease called sleeping sickness in humans and nagana in livestock.

Tsetses make cattle so sick, but they can't be raised efficiently in a region of Africa the size of the United States.

MAN: Coming back to the first trap we set.

NARRATOR: People are trying to control them with things like baited traps.

MAN: It looks like it's got a lot of tsetse flies.

Holy cow.

That's a lot of flies.

MAN #2: The tsetse flies.

NARRATOR: They're effective, but more defenses are needed.

That's where Geoff Attardo at the University of California, Davis, hopes to help.

He's trying to stop tsetse flies from making babies in the first place.

A female only mates once in her life-- enough to make the ten or so babies she'll have.

The male makes sure she doesn't mate again by delivering a substance that makes her lose interest in sex.

Scientists are trying to figure out what it is.

If they could bottle it and spray it, female tsetse flies may never get busy at all-- no more tsetse offspring to worry about.

After spending about a month below ground in a hard shell, the fly emerges as an adult and unfurls its wings.

Like us, tsetse flies ensure the next generation by investing a lot in a few offspring instead of investing very little in a lot of them.

They grow up so fast, don't they?

Hi, it's Lauren.

We have a few other episodes about insect moms.

Blue orchard bees build nests that look like stunning jewels and gall wasps trick trees into making their young a glitzy mansion.

See you next time.