New York City has 25,000 restaurants –  not counting the pizzerias – and millions of home chefs.

Three nights a week, their  trash ends up not in a dumpster, not in a can with a lid…but right on the curb.

And that’s when the rat buffet begins.

They say if you can make it  in New York, you can make it anywhere.

And rats…well, they made it.

But how did they get here in the first place?

And how do we make them go away?

I’m Shane Campbell-Staton, and this is Human Footprint.

As a New Yorker, I always lean towards pepperoni.

I can respect that.

Bobby Corrigan is one of those 8 million New Yorkers.

He loves everything about  this place: a good slice of pepperoni, the city lights, and oh yeah…rats.

In college, I had to save money, so I took a job as an exterminator.

They put me in the sewers  right away, and I thought, oh, this is cool.

Literally working your way  from the bottom up.

Exactly.

Bobby spends his free time writing poetry on the street… but by day,  he’s a world renowned Urban Rodentologist.

Are rats the scourge that  people make them out to be?

I admire them.

I respect them.

However, they live in dirty areas.

And that dirt got cooties.

It’s viruses.

Bacteria.

Fungi.

Protozoans.

55 different diseases.

55?

55.

Wow, okay.

And think of the plague, Shane.

I mean, 25  million people go down with the black rat and their fleas.

Yeah.

No place needs Bobby’s expertise  more than New York, where it seems like rats are… pretty much everywhere.

Here we are, sitting at a restaurant.

If that door over there is not pest proof into the  pizza shop across the kitchen counter and urinates and defecates and leaves  the film.

And then someone touches the film the next morning and then, boom.

This pizza’s tasting a little less good now.

Yeah.

It was time to walk off that pizza on what Bobby calls… a Rat Safari.

We're going to cross over here, Shane.

There's a park here.

Here we are, almost at the end of  June.

Their breeding season is in full swing.

Love is in the air.

Love is totally in the air.

And families are growing.

We know that rats are the most prolific of all  mammals.

A single pair of rats would become 360  million in the short space of three years.

As the sidewalks begin to deteriorate, rats  will move below the sidewalks for their burrows.

You’re literally sometimes walking  right over the tops of the heads of rats.

Sometimes rats will go right up the  tree…if there’s a bird nest up there,  they’re predacious on those birds.

Is the reason why you're wearing the hard hat  because a rat might jump out of the tree onto you.

And is that something I need to worry about?

Actually, that would be cool if they would  jump onto me.

I'd like that a lot.

Okay.

The longer rats live in our cities, the better they get at it…  and the harder we try to keep them out.

Here we have something that's very common:  the bait box.

The rats will go inside that box and find the poison bait.

And eight,  nine, ten days later, they die.

But no matter how much poison we throw at the  problem… We're also throwing rats a lifeline.

Food in a big city of high density  humans is extremely reliable.

So this becomes like basically the rat buffet.

It does.

It’s hard to imagine New York City without rats…  so how did they become such a fixture here?

If we want to know the story of rats in New  York City, we have to know what were they doing before they got here.

This is Jason Munshi-South.

He’s a biologist who loves New York City  almost as much as he loves rats.

When the brown rat made it here,  it sort of hit the jackpot.

The brown rat, or Rattus norvegicus, probably  originated in East Asia, where it was first drawn to human settlements by agriculture.

But as people around the world moved into dense cities full of trash, human waste, and safe  hiding places, rat populations soared.

Without meaning to, we built a rat paradise.

Rats don’t have to go to much trouble to find homes because we provide these for them.

Made  to order.

Everything but the welcome mat.

It’s like, hey.

There’s this massive  free food here now and all I gotta do is hang around these people.

At the height of European imperialism, rats were already entrenched in cities  and ports across the Old World.

So, when European explorers sailed west  into the unknown, rats did what they've always done, and came along.

How do we know what we know about how rats spread across the planet?

We extract DNA out of those bits of rat from around the world, and then we look  at either the whole genome or portions of the genome and we compare the genetics of a rat  from Thailand to all the other populations.

You start to see the historical narratives  will roughly match up.

Then, you see this massive number of populations that are all closely  related around the period of European imperialism, and it matches Western Europe and  all the places they went.

Where we are now is where the Dutch bought  the island or stole the island.

I put my money on stole, but go ahead.

By the early 1900s, it wasn't just white human settlers who’d colonized all of  North America.

It was also rats.

But not all rat habitat is created equal.

Yeah as you’re driving from Battery Park where the rats first came in, up to here.

And this is one  of the great rat neighborhoods of the world.

But if you keep rolling north,  the whole vibe changes.

And Jason’s got the data to prove it.

We got basically about 70,000 points where rats have been identified.

And this  is the outcome of the map, where the green areas are really good rat neighborhoods like  where we are right now, right about there… Okay Near Tompkins Square.

But then see this red area here south of Central Park?

Uh-huh.

That's Midtown where there isn't a lot of  residential.

The companies pay extra money to have the streets cleaned up.

And it seems to  create this almost like dead zone for rats.

Jason can predict the size of the rat  populations in different neighborhoods by looking at data on humans.

Areas that are highly residential and mixed commercial that have a lot of restaurants,  super predictive of rats, not surprisingly.

And older neighborhoods with older  buildings, they really like that.

The places where rats have food to eat and  places to hide are the places they thrive.

On the flip side, take those things  away and the rats disappear too.

It seems so simple.

And yet somehow… Go to any city around the world that’s plagued with rats.

We are not winning this war.

Rodenticides, or rat poisons, have become a go-to weapon in the war on rats.

But rats are  becoming resistant, pushing people to switch up the formula and apply even more rodenticides  to keep rat populations in check.

And it’s not just poisons… Our campaign against  rats has grown into a 3-billion-dollar-a-year effort, involving legions of  people around the world.

We’ve even conscripted other  species into the war effort.

Alright, so this is our service center.

It’s like the gym, play, house, sauna, exercise room, all together Yeah all together, all together.

When Scott Mullaney and his wife Angie  aren't cruising down a scenic highway, they’re training little dogs to do a big job.

Instead of poison or traps, their company   uses dogs to kill rats.

It’s actually nothing new… As cities grew bigger and  denser in the 19th century, rat populations exploded and people created  whole new dog breeds just to kill them.

We’ve worked them on top of twelve story  buildings.

We've worked them in supermarkets.

We've worked them on airplanes.

We’ve worked them  on trains, trains, planes and automobiles.

I mean, really, any environment you can think of.

Over the years, Scott and Angie’s small team has killed more than 30,000 rats.

Alright, we’re gonna leash up.

Here ya go kid.

There ya go.

Dogs always give  100%.

They just love what they do.

We're just gonna finish up, so  we can close up and go.

Last but not least.

Is it more difficult with city rats than it would be for like rats around  like a farm or something like that?

It's a totally different application.

The rats are used to cars, maybe people screaming, just other normal city things.

All of a  sudden, you're bringing a dog ...

They're used to dogs walking around, barking, peeing,  or whatever the case may be, they're not used to a dog coming and eliminating them.

My nerves are going a little bit.

I'm a little nervous, a little anxious about what's  going to happen.

Also, a little excited.

A quick warning: the next scene gets a little  intense and graphic.

If you’re squeamish, feel free to skip ahead 45 seconds.

With  that out of the way, back to the rats… Okay, guys.

So what we're going to do is we're  just gonna take the leashes off the dogs.

I want to start right over here.

You can see his kinetic  energy, he just, he's on point right now.

He knows what the deal is.

It looks like chaos, but this is actually highly coordinated.

The dogs find the rats with their keen noses, the handlers move dumpsters and palettes to  expose them, and the dogs finish the job.

Yep.

Inside the bait box Oh, and the hockey sticks?

Those are for cutting off escape routes.

Wooo!

Oh!

The dogs look like they’re having a blast!

The rats?

Well, not so much.

It’s still alive.

Hold on for a second.

Yeah, just make sure that nothing takes off the other way.

Good job guys!

Okay, we got something over here, I think.

There are things that I have seen that I cannot unsee, and I will be having a whole different kind of nightmare from now on.

What do you think our situation with rats says about us?

I think it's pathetic.

As long as human beings continue with their sanitat[ion], poor sanitation habits, okay?

And their lack of concern, we will never get rid of rats.

They’re here to stay.

Do you think rats, do they have as much of a right to be called New Yorkers as people?

If somebody asked me, "Would you like to officially exterminate Rattus Norvegicus from our cities?"

The answer, for me, would be no.

Because there's another flip side to this thing that a lot of people don't even put together and that is the reason you and I can be healthy or our lifespan has increased dramatically from the 1700s and the 1800s is because we owe the thanks to the rats, and the mice.

We've benefited from everything of testing every drug, every cancer drug, every pharmaceutical, with cosmetics, the rats got us our longevity.

And so here's that paradox of, on one hand we revile this animal, we hate this animal.

On the other hand, we should be saying thank you.

If you want more Human Footprint, you can tune in to the full length series on the PBS App or on your local PBS station.