Return of the Flesh-Eaters

Summary

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Radiolab – "Return of the Flesh-Eaters" (March 13, 2026)

Episode Overview

In this episode of Radiolab, hosted by Latif Nasser with producer Sara Khari, the team takes listeners on a deep dive into the bizarre and haunting story of the New World screwworm—a flesh-eating fly whose eradication once marked a landmark scientific intervention but has now made a concerning comeback. The episode blends scientific history, current events, and bioethics, posing one of the thorniest questions in conservation and human intervention: is it ever justifiable to drive a species to extinction?

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Key Discussion Points & Insights

1. The Screwworm Crisis Returns

• Background: In 2016, the Florida Keys saw a mysterious outbreak of gruesome wounds on its endangered key deer population.
  • Sarah Zhang: “People suddenly started noticing all these, like, ugly, like, gristly wounds on these deer.” [02:48]
  • Sara Khari: "Gaping holes or wounds in their neck... you could see down to the bone." [02:53]
• The culprit: The New World screwworm fly—once eradicated from the U.S.—laid its flesh-eating larvae in open wounds, causing severe suffering and death in wildlife and livestock.
• This event rekindles public health fears and scientific debates about eradicating dangerous species.

2. The Science and History of Screwworm Eradication

The Screwworm's Life and Impact

• Sarah Zhang describes the screwworm as a fly, whose larvae (maggots) burrow into flesh with "a horrifying mouth... twist themselves down... and eat the flesh." [07:14]
• Historically, screwworms devastated ranchers and livestock in the southern U.S., causing huge economic losses.

The Genius of Edward F. Knipling

• Edward F. Knipling (entomologist) grew up battling screwworms as a farm chore— fueling a lifelong quest to stop them.
  • "Screwworms used to strike fear in the hearts of ranchers all throughout the Southern United States." [06:31]
• Key innovation: Realizing female screwworms only mate once, Knipling hypothesized releasing sterile males en masse could crash the population.
  • Sara: "If he could just make the males sterile... and trick the female screwworms into mating with these sterile males, the females aren’t going to lay any eggs that are viable." [10:33]
• Early attempts involved surreptitiously irradiating screwworms in military hospital X-ray machines to create sterile males. Initial field tests failed on Florida’s Sanibel Island but succeeded spectacularly after scaling up production in Curaçao with insect "factories." [13:08–16:02]
• The approach spread from Florida, across the southern U.S., and through vast international collaboration, eventually eradicating screwworm from all of North America by 2006.
  • "And in 2006, all of North America is declared screwworm free." [19:10]

Maintenance & Economic Impact

• Maintenance: Ongoing “sterile insect barrier” at the Panama–Colombia border costs only $15 million/year, saving over $1 billion in agricultural losses each year. [20:06–20:27]

3. The 2020s Outbreak: Screwworms Return North

The Current Outbreak

• In 2023, Panama saw a dramatic spike in screwworm cases, increasing from 25 per year to thousands—eventually spreading through Central America and encroaching on the U.S. border. [25:05–25:40]
• Theories for resurgence: decreased effectiveness of sterile flies, COVID-related disruptions, cattle smuggling, and global interconnectedness allowing reintroduction from South America. [25:51–26:27]
  • "It's not a matter of if the deadly pest gets to the US, but when." [26:34]
• Governments respond: The USDA and CDC reinvest heavily, establishing new fly factories and border surveillance measures, preparing to release up to 500 million sterile flies per week. [27:13–27:48]

Human Dimension & Public Health Concerns

• The screwworm is not just a livestock threat; outbreaks now affect wild animals, pets, and humans—“over 1000 human cases, and the number continues to grow daily.” [29:48]
• Megan Nichols (CDC): “They are often attracted to mucous membranes. So eyes, nose, ears, urogenital… a patient was holding a bowl in which they were basically sneezing out and pushing out larvae from their nasal passage.” [29:30–30:22]

4. Ethics of Eradication: Should We Drive a Species to Extinction?

The Gene Drive Debate

• Scientists are exploring gene editing (“gene drive”) to wipe out screwworms permanently—potentially “extincting them off the face of the planet forever.” [33:11]
• Gene drives can ensure a “killing gene” is passed almost 100% of the time, effectively dooming the species.
  • Latif Nasser: “That feels wrong. That feels like we untake. Backable.” [33:15]

Gregory Kaebnick and the Bioethics Panel

• Gregory Kaebnick (Hastings Center) convenes a symposium of environmental ethicists, ecologists, and geneticists to weigh ecological and philosophical pros and cons.
  • Kaebnick: “Here we are in the early stages of the sixth major extinction, one that we humans are causing. And I mean, in a way, this seems like, gosh, joining forces with the other side in some way.” [33:43]
• Key ethical questions:
  • Does screwworm have a valuable ecological role (pollinator, food source)? (Summary: Minimal.)
  • Is it a matter of valuing “the ingenious development [from] millennia of evolution”? [37:12]
  • Might removing screwworms have unintended ecosystem knock-ons (“hubris” argument)?
  • The panel’s reluctant consensus: screwworms are a rare candidate where full global eradication seems ethically justifiable.
    • “Most people had... said, yeah, screwworm looks like a pretty good candidate, really, that it would be okay to wipe this species off the planet forever.” [38:16]

The “Undo” Button

• If future regret arises, it may be possible to revive screwworms from preserved samples (“de-extinction”). [42:02–42:37]
  • Latif (joking about a public campaign): “We're just gonna drop these flesh-eating worms... we're just gonna rain them down over you and your home.” [42:52]

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Notable Quotes & Memorable Moments

• On the logic of eradication:
  “The only way you get rid of the disease is by getting rid of the fly.” — Gregory Kaebnick [40:38]

• On the ethical discomfort:
  “I don’t want us to have to live with these, but I don’t want us to kill them forever. That feels wrong.” — Latif Nasser [33:15]

• On evolution and intrinsic value:
  “Anything that's around today has been honed by millennia of evolution... a marker of the creative natural forces that sustain life that brought us into being.” — Gregory Kaebnick [37:16]

• On the horror of human infection:
  “A patient was holding a bowl in which they were basically sneezing out and pushing out larvae from their nasal passage.” — Megan Nichols, CDC [30:22]

• On the outrageous science origins:
  “Watching insect sex all the time—not in a weird way.” — Sara Khari [12:16]

• Golden Goose Award:
  “If you ever meet someone who doesn’t believe that the government should fund basic science, just one of these [stories]—we’ll link them all in the Episode Description.” — Latif Nasser [44:18]

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Timestamps for Key Segments

| Timestamp | Segment | | ----------- | ------------------------------------------------------------ | | 02:30–04:44 | Introduction and Florida deer outbreak | | 05:15–12:36 | Origins: Knipling’s life, theory, and first experiments | | 13:37–16:02 | First mass production, field success on Curacao | | 16:37–20:27 | U.S. eradication campaign and multilateral expansion | | 24:27–26:34 | 2023–present: Screwworm resurgence and government response | | 28:11–30:22 | Broader impact: wild animals, human cases, CDC perspective | | 31:08–34:11 | The treadmill: Are we stuck in perpetual eradication cycles? | | 34:11–38:16 | Ethics panel: Should we eradicate a species forever? | | 40:38–41:11 | The limits of alternatives: no medicine, only eradication | | 42:02–42:37 | The “undo button” and de-extinction | | 43:20–44:47 | Golden Goose Award and the value of basic science |

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Episode Tone

The hosts strike a tone that is at once deeply curious, slightly irreverent, and ethically inquisitive—moving deftly between wonder at scientific genius, horror (and occasional humor) at the parasite’s gruesomeness, and humility regarding human intervention in nature. The debates are lively, patient, and nuanced, ultimately leaving listeners with no easy answers—and an enduring respect for both human ingenuity and the unpredictable complexity of life.

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Resources Mentioned

• For further information: screwworm.gov [45:15]
• Sam Kean’s podcast "The Disappearing Spoon" (episode on screwworms)
• Sarah Zhang’s article in The Atlantic (linked in episode description)
• Radiolab’s gene drive episode: “CRISPR Update”
• Golden Goose Award: examples of basic, “silly-sounding” science with transformative impact

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Summary Produced by Radiolab Podcast Summarizer, 2026.

Transcript

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[A]

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[B]

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All right. Okay. All right.

[C]

You're listening to Radio Lab.

[A]

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[E]

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[A]

Hey, I'm Latif, this is Radiolab, and today I have with me asara.

[B]

Okay, no echo or anything?

[A]

Nope.

[B]

Okay, great.

[A]

As in Radiolab reporter, producer, Sara Khari. Can you hear me without an echo?

[B]

Oh, yeah, no, you sound great. And Sarah's here in the studio.

[A]

I have a Sarah.

[C]

Hello.

[B]

Hi.

[C]

Hi. Nice to talk to you.

[A]

Sarah Zhang, who writes for the Atlantic and is a wildly prolific science journalist.

[C]

Oh, thank you.

[A]

Like, I feel like you cover Covid. I know you cover autoimmune diseases. I know you cover Ozempic.

[C]

I'm sort of lucky enough to cover just, like, whatever I'm interested in, but

[A]

we called her up because a while back, she noticed something weird happening. Happening to the deer in the Florida Keys.

[C]

I don't know if you know about the key deer. They're, like, really cute. They kind of like, wait at bus stops and people like to feed them.

[A]

Okay.

[C]

And so back in 2016, it would

[B]

be a very grave situation for this endangered.

[C]

People suddenly started noticing all these, like, ugly, like, gristly wounds on these deer.

[B]

Gaping holes or wounds in their neck or in their. In their head.

[C]

Literally, you could see down to the bone.

[E]

Gruesome, painful. It's a very sad story.

[C]

So it was, you know, it was kind of like a weird thing happening in Florida story.

[B]

Yeah. But volunteers are teaming up to treat affected animals.

[C]

What it turned out was that there was an infestation of an insect called

[A]

the New World screwworm.

[E]

New World screwworm.

[C]

The New World screwworm, also known as flesh eating worm.

[F]

Oh.

[C]

And like, I had never heard about school worms before. Yeah, me neither. I would imagine most Americans have never heard about school worms before. And the reason we don't know about it is because it's been eradicated from our country. Huh. I was like, what? Like, that's crazy. I've never heard of, like, an insect being, like, completely eradicated from our country.

[B]

And as Sarah started to dig into

[C]

this, it got even crazier and crazier.

[B]

What she found was the kind of amazing story of one of the biggest, biggest environmental interventions that humanity has ever undertaken. And the story of this worm, this honestly nightmarish flesh eating parasite that, despite those efforts, is right now today. Back in the news.

[D]

We are on screwworm watch and we

[B]

are ready forcing public health officials and ranchers and ethicists.

[F]

Here we are in the sixth major extinction that we humans are causing to

[B]

ask maybe one of the biggest questions that we as beings on this planet can ask.

[F]

Would it ever be okay to bring about the extinction of a species?

[A]

Oh, boy.

[E]

Yeah. But, I mean, these are about the worst parasite on Earth. I cannot imagine anything worse than these guys.

[A]

So one of the first people we called when we got into this whole screw worm thing was the author, Sam Keene.

[E]

My name is Sam Keene. I am a science writer.

[A]

Because it turns out he, like Sarah, at some point, had fallen into the screwworm hole.

[E]

Yeah, I had never heard of them. And I started Googling and then I went to Google Images and I immediately regretted doing that.

[A]

And according to Sam, the reason that none of us had ever heard about what he called the worst imaginable parasite on Earth is. Is because of something that in 1970, the New York Times called the single

[E]

most original thought of the 20th century.

[B]

And it turns out that thought was born in the brain of a man named Edward Nipling.

[C]

Edward Nipling

[B]

So, as you know, Latif, when we first learned about this, I got obsessed and started doing some digging and learned that nippling has unfortunately passed away.

[E]

Dr. Edward F. Nippling, we're happy to

[C]

be here in your home today, and thank you for participating in this oral history.

[B]

I found this whole trove of interviews that he did back in the day. If you could start, please, by telling us when and where you were born.

[F]

I was born in port Lavaca, Texas, March 20, 1909.

[B]

Nibling grew up on his family farm in Texas.

[F]

And in those days, farming was a very difficult occupation, honestly.

[B]

Mostly because of the. What was I supposed to say after that?

[F]

The screw worms.

[B]

Oh, mostly because of screwworms.

[C]

Yeah. So it was. It was a problem for ranchers, actually, I think this is a quote. I remember it was. Screwworms used to strike fear in the hearts of ranchers all throughout the Southern United States.

[A]

Could we actually. Could you just tell me what a screwworm even is?

[C]

It is a fly. It has kind of like.

[A]

Why do they call it a worm if it's a fly?

[C]

Well, flies are also maggots, right? Like, our flies come from maggots. So the maggot phase is a worm.

[A]

Okay, okay, okay.

[C]

So basically what they do is that if you have a little, like, nick in your skin, a little wound, even

[E]

something as small as a tick bite,

[C]

these flies would lay their eggs in

[E]

Those wounds, roughly 400 eggs at a time.

[A]

Oh, my God.

[C]

And then these maggots essentially would come out. They kind of look like a small white thread.

[E]

They have this kind of horrifying mouth with two sharp teeth and a little ridge on their body that sticks out exactly the way the threads on a screw do. They would twist themselves down, kind of

[C]

burrow themselves into the flesh like a screw, and they would eat the flesh. Yeah, it's.

[E]

And they are extremely hard to get out once they have locked in.

[F]

A screw worm would get into the calves when they were born.

[B]

And so back to young Edward Nipling.

[E]

He got probably the worst job on the farm, which was to pick the screwworms out of the family's cows.

[F]

And that was a very unpleasant task.

[E]

Have to try to yank them out of these animals that obviously aren't happy about this.

[A]

Is there a tool you used? Like, what are you.

[E]

I'm guessing a tweezers or just fingers.

[A]

Screwdriver. You gotta use a screwdriver.

[E]

That was his job. And it introduced a lifelong hatred of screwworms in his heart. You know, understandably so.

[B]

But at the Same time, you know, he has sort of a scientific bent of mind. He's curious.

[E]

He was actually kind of fascinated by insects.

[B]

Over time, he became a bug nerd.

[E]

Definitely a bug nerd.

[B]

Even named his cats after insects, one

[E]

after a mosquito and one after a boll weevil, entonymous and culex.

[B]

And when he grew up, grew up

[E]

to be an entomologist, but also kind of in the back of his mind, he was always thinking, I, I have to figure out a way to control screwworm. I want to put a stop to them somehow.

[B]

And as it happens, the first job I had, in the late 30s, he got a job at the USDA as

[F]

an entomologist working on the screwworm. That was the Bureau of Entomology and planned quarantine at that time.

[C]

And then World War II breaks out

[B]

and the military enlists him in developing,

[F]

I mean, insecticides and repellents for use for the armed purposes.

[C]

He actually ends up helping develop ddt.

[A]

Oh, yeah, heard of that one.

[C]

And this is actually sort of part of his journey, which is that he saw insecticides can be really effective, but they can also be really devastating for the environment.

[B]

So after the war, when he gets back to his screw worm job, he's just thinking about this problem, like, how

[C]

can we figure a way to control insects that does not require spraying lots of poisons?

[B]

And his way of trying to figure that out is watching screwworms mate.

[C]

Just watching a lot of insect sex as one does.

[A]

Like, yeah, why? Why?

[C]

I think he was just trying to understand these pests, right? To think, like, what could we do about it, huh?

[B]

And so one day a colleague of Nippling's is, you know, watching the screwworms have their sexy times and he makes

[C]

this observation that sounds like maybe not that important or not that interesting, but

[E]

that kind of hinted at something, he wasn't quite sure what exactly.

[C]

Which is that females only mate once,

[E]

whether or not they get pregnant. They get one shot to have intercourse and try to have eggs.

[B]

I really feel for these females. Like, this is such a high stakes. You have to have the best sex of your life in that one time.

[E]

Yeah, that's it.

[B]

But Nippling, he's looking at this and he's like, wait, if he could just

[C]

do something to all of the males, right? Like, if he could just make the

[B]

males sterile and then if he could trick the female screwworms into mating with these sterile males, the females aren't going

[C]

to lay any eggs that are viable

[E]

that would essentially take those females out of circulation for reproduction purposes.

[B]

Their one shot would just be doomed to fail, basically.

[E]

Yes, exactly.

[C]

So just like somehow flood the zone with sterile males is the idea.

[B]

These poor females already had it so hard, and now he's just like, ruining the dating pool for them.

[C]

It's a little diabolical from the fly's

[B]

perspective, but lucky for these screwworm ladies,

[E]

it wasn't like that was a very

[B]

practical idea, because how would you even pull that off?

[E]

You know, how do you mass sterilize a bunch of insects?

[F]

But then he finds a paper, an article, scientific magazine.

[C]

Basically, Since World War II, there's sort of like a lot of interest in, like, what can we do with radiation.

[A]

Oh, of course. Right, yeah.

[B]

And this paper was by a geneticist who was saying that it was possible

[F]

to sterilize fruit flies by exposure to X rays.

[E]

And I think he sort of jumped off of his couch and said, oh,

[F]

my God, maybe we could sterilize through work.

[E]

This could be the solution to the problem.

[A]

Okay, so what, yeah, what does he, what does he do?

[B]

Well, so the thing he needs is a bunch of X ray machines, but

[E]

he decides he's not going to go public and try to get any funding for this.

[F]

We knew that if the media got ahold of that, they could make quite a deal out of this.

[B]

I mean, remember, he's working for the government. Like, taxpayer money is at stake here.

[C]

What happens if the press gets hold of this and then we're just totally ridiculed for, like, wasting money or watching insect sex all the time?

[B]

Not in a weird way.

[F]

Yeah, we were rather cautious about that.

[E]

So he decides he wants to do this kind of on the down low.

[B]

And basically he gets one of his

[E]

colleagues to take a bunch of screw worms and sneak them into a nearby military hospital and use the X ray machines there.

[B]

Flesh eating worms in a hospital. Great.

[E]

Yeah, exactly.

[B]

But how does he get the screw worms in?

[E]

Unfortunately, we don't have many details about what he did to actually get inside there. I pictured him hanging out at the loading dock at night and grabbing the door right before it shuts. Or Watergate taping the lock or something like that, Sneaking through the hall. I believe they did this at night, too. He had to be kind of clandestine about it, Sneak around a little bit,

[C]

and they are literally putting these flies through the next machine and be like, hey, what happens?

[B]

But the problem with shooting a bunch of radiation at a bunch of flies

[C]

Is that you create all these mutations, A bunch of random mutations. So you might just kill the fly. That's kind of a problem.

[A]

Right.

[C]

So they found that they figured out the right dose, but they also figured out exactly when to put them through radiation. It's when the fly's testes are developing. Right. Cause that's like what you really want to knock out. So that happens to be between 5.5 and 5.7 days.

[A]

So it's like they've got it to within hours.

[C]

Yes, yes.

[B]

And when they do that. Bingo.

[C]

It seems to work.

[F]

But of course, the next thing was would they perform in. In a natural population.

[B]

It's not enough to just do it in a lab.

[E]

So then he decides it's time for a real world test. And he found an island off Florida

[F]

on the island of Sanibel.

[E]

Sanibel Island.

[B]

He shows up there with some of the radiated screwworms from his lab, releases them on the island.

[E]

And it did not work.

[B]

Like the population of screwworms stayed pretty much the same.

[E]

The experiment failed. And Nippling was glad he hadn't said anything or, you know, gone after public money.

[B]

So. Yeah. Does he just resign to his failure?

[A]

That's the end of the story. Yeah.

[E]

No, not at the end.

[F]

Kind of stymied what to do for a year or so. And then I got a letter from a veterinarian on the island of Curacao,

[E]

a Dutch island called Curacao. Where is Curacao? Off the coast of Venezuela. He wrote a letter and said, the goats here are being ravaged. I know you study this. Can you help us in any possible way?

[F]

And I thought, well, this is just the place that we're looking for.

[B]

And this time Nippling wants to go all out.

[E]

They were not going to take a chance that there would be too few flies.

[B]

Like no more handful of flies from his rinky dink lab.

[E]

They were gonna set up an industrial facility for making these flies and like carpet kurasau and really overwhelm them with the sterile males to make sure that they were doing everything they could to give this experiment a chance of success.

[B]

So in this factory that they set

[E]

up, they came up with a formula for the food that they were going to feed them.

[A]

Okay.

[B]

And it was ground horse meat that

[E]

they so soaked in blood and they would let that get putrid and then they would douse it with formaldehyde.

[B]

Oh, okay.

[E]

So, yeah. And it was cheap enough to get, you know, so they knew they could produce a lot of this stuff pretty quickly.

[B]

Okay, why the formaldehyde? I don't know why that's such a weird.

[E]

Apparently they just like the Formaldehyde, I don't know.

[A]

It's just a little extra kick. It's like hot sauce for them.

[E]

So then from about March 1954, they are producing 170,000 of these sterile adults per week.

[B]

They are feeding them this slurry, though at this point, without the formaldehyde, it

[E]

took 40 tons of the slurry to get that job done.

[B]

Wow.

[E]

And it was a smashing success. The population plummeted after they started releasing these flies. His big idea had worked back in the United States.

[F]

The livestock people, especially ranchers, catch hold of this. They came to us and they're like,

[C]

wait, we really want this?

[E]

Eventually, the clamor from ranchers got so big, Nippling decided, well, I think the

[B]

time is right to try rolling out his screw worm strategy in the U.S. and so, armed with some funding from the USDA, this new technique for insect control is eliminating screwworms.

[E]

The first big push started in about 1957 in Florida. And after about two years of dedicated work, they had eliminated them, not just

[B]

in Florida, but everywhere east of the Mississippi.

[A]

That is huge.

[C]

And then kind of keeps going west.

[B]

The Texas Cattlemen's association hears about it.

[E]

I mean, it was a Texas sized problem that they had.

[B]

They want in too. So Nipling and his team end up

[C]

building a really big factory in Texas.

[E]

Eradication headquarters at Mission, Texas.

[B]

Here, millions of screwworm flies are being reared each day.

[C]

All these, like, metal machines.

[B]

Sarah told us about a similar factory she went to in her reporting.

[C]

Many different rooms, sort of like all at different temperatures, different humidities for each phase of the life cycle.

[E]

I could not have imagined. It smelled good.

[C]

I'm sorry to say this, but what it reminded me of was the smell of a used tampon.

[A]

Okay, it makes sense.

[C]

Blood that's gone a little bit bad.

[B]

Maybe from these factories, they start releasing flies multiple times a week.

[A]

So how did they do that?

[C]

By airplane?

[F]

These planes are being loaded with sterile male screwworm flies in Mission, Texas.

[C]

Basically, they would fly these little prop planes and release these flies in the air.

[E]

They took them up in refrigerated boxes. They had to buy essentially cases of perfume and cologne and dump them on the boxes before the pilots would allow them in the airplanes. And then they would essentially open the hatch and just dump them out and let them fall down.

[B]

Oh, wow. And at this point, the nippling strategy is working so well. Screwworms are disappearing from all of the Southwest.

[E]

They started marching their way down to the border. Yeah, pushing it down, pushing it down.

[C]

Eventually, people were like, well, screwworms obviously don't respect national borders.

[F]

If we're really going to deal with a screwworm problem, we would have to enlarge the program.

[C]

What if we just kept going?

[F]

This operation can now expand into Mexico,

[E]

you know, get them out of Mexico. Then we go down country by country through Central America.

[A]

That is so much ground to cover.

[E]

Yep.

[B]

And so all through the 70s, 80s,

[C]

90s, there are all these kind of international agreements.

[E]

Frankly, this was a tough sell in some places because the US has a history of meddling in Central America.

[A]

Right.

[E]

Especially in this time.

[B]

But despite that, and despite, despite political

[E]

turmoil, revolutions and coups and things like that.

[F]

Holy.

[E]

The disgust over screwworms was enough that

[B]

all seven countries in Central America came

[E]

to the table and they started marching down, you know, a dozen miles at a time or so, just working down year by year, all the way down to the border between Panama and Colombia.

[B]

And in 2006, all of North America is declared screwworm free.

[A]

Wow.

[B]

And that so called single most original thought in the 20th century changes the face of the entire continent.

[A]

Amazing.

[C]

And to this day, at the time I was reporting it like there's still a factory in Panama, it's still producing millions of squirms, growing millions of screw worms every day. Flying a plane, I think that was three times a week, and maintaining this like, basically this, what they called of it, like a sterile insect barrier.

[B]

The idea is that that area where

[C]

Panama meets Colombia, the Djarian Gap, which I think it's been used a lot for other reasons, that's like the most

[A]

dangerous area for migrants, right?

[C]

Exactly.

[B]

But it's also one of the narrowest parts of the Americas, only about 60 miles wide.

[A]

Okay. So it's like a natural choke point.

[B]

Right. And because of that, maintaining that sterile

[E]

screwworm barrier only costs $15 million per year, which is a pretty reasonable price compared to the huge cost if screw arms were just kind of running wild.

[C]

Yeah. So when I was preying on this back in 2020, the money saved was estimated to be over a billion dollars a year. So $1 billion saved compared to 15 million cost.

[A]

Wow. So that's a pretty good return.

[C]

And obviously it was more expensive when you were in the active eradication phase.

[A]

Right.

[C]

But the maintenance cost, you know, just really not that much money for a government program. And it's just kind of an example of like how when with basic science, you don't always know exactly where it will go. But in this case it ended up like creating this continent wide multinational collaboration that has been going on for decades and decades. And the fact that this all kind of started with someone like watching squirrels meet in the lab and having an epiphany is kind of remarkable.

[B]

Now, there have been a couple of small outbreaks here and there over the years, including the Florida one, the deer, right? 2016 one. Yeah, but they've all gotten tamped down pretty easily. Like it didn't take all that much to beat those back. But when we come back from break, all kinds of things are gonna break loose. News, biological barriers, and maybe also Latif's heart.

[D]

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[A]

This is Radiolab. I'm Latif Nasser here with producer Sara Khari.

[B]

Hello.

[A]

And we've been talking to journalist Sarah Zhang and writer Sam Keane about

[E]

screwworms.

[B]

Right, the skin crawly, flesh eating parasite that we all forgot about because Nipling and his sterile flies drove it down south.

[A]

All the way to a biological demilitarized zone at the very bottom of North America, aka the southern border of Panama.

[C]

Yeah, but in 2023, Panama suddenly started

[B]

seeing a massive spike in screwworm cases. From like 25 cases a year to like thousands.

[E]

And since then, it's only gotten worse.

[B]

The parasitic fly is moving north.

[E]

They have been steadily marching north.

[C]

They've been found in Costa Rica, Nicaragua,

[E]

Honduras, El Salvador, Guatemala.

[C]

They're even In Mexico, only 700 miles

[E]

from the U.S. border.

[B]

And it turns out it's basically getting closer every day.

[E]

Less than 400 miles.

[F]

300 miles from Texas on the southern border.

[E]

It's gotten as close as 70 miles or so from the US border.

[A]

Whoa.

[E]

This is an ongoing breaking news story.

[A]

So what happened? Like, how did they get past the biological wall?

[E]

There are a couple of theories.

[C]

One theory is that maybe the strain of Scurum that they were growing at the factory was not as effective anymore. I don't know. Maybe the ladies out there caught onto what was going on and weren't mating with them or something.

[E]

Just general disruptions due to Covid might have weakened the production a little bit.

[A]

Or maybe Sam says, given that we live in a more and more interconnected

[E]

world, because it does still exist in

[A]

South America, where people and products and animals are moving from place to place, it was just a matter of time before these worms found their way through.

[E]

The best guess is that people were smuggling cattle that were infected and then it just got out.

[B]

But regardless, as of today, right now,

[C]

the screwworm, it's sort of like knocking on our doorsteps.

[E]

It's not a matter of if the deadly pest gets to the US but when.

[B]

And surprisingly enough, in this time of cuts to science funding and all that, and you know, the idea of building political will around something that everyone has pretty much forgotten seems dubious.

[D]

The issue has also alarmed Washington.

[B]

It actually does seem like the US Government is paying attention.

[F]

The US Department of Agriculture has snapped

[B]

into action and really just like Nipling's time, pretty much because of the cattle industry.

[F]

Billions of of dollars of losses a year.

[A]

Of course, it could truly crush the

[F]

cattle industry as well as other livestock industry in Texas.

[B]

So the USDA has started to set up screw worm traps along the US Mexico border, shut down the southern border. They have agents on horseback, so called tick riders, patrolling the border for stray cows. They are pouring money into to screwworm research. And of course they are rebuilding Nippling's fly factories.

[E]

They are now building a new facility down in Texas, another one in Mexico.

[B]

All told, probably in the next couple years, we will be producing and releasing something like 500 million flies per week.

[A]

Wow.

[B]

And we probably will have spent like hundreds and hundreds of millions of dollars.

[A]

Do you see this as like the modern cow factory farm system is like unsust sustainable and like this is just like one other band aid to keep that system financially profitable or something? Like I could see an argument that's like, oh, this is just to help like big rancher businesses.

[C]

Yeah, well, I think in a, in a literal sense, like this program was created to help ranchers. Like that is in fact the express purpose of the usda. So I think I wouldn't, I wouldn't even argue with that premise. But this does affect wild animals too, right? In Central America, like used to see like howler monkeys fall out of trees because they had become so disfigured and sick from getting infested by squidworms.

[B]

And beyond that, I mean, actually, you know, this time around with this effort, it's not just the USDA that's involved in this program.

[D]

So I'll try and make the case on the human side of things, number one.

[B]

So I talked to this public health official named Megan Nichols who is at

[D]

the cdc and my current role is incident manager for our new world Screwworm response.

[B]

Because the CDC is worried about this outbreak too. And the thing that Megan pointed out

[D]

is that these flies like to infest a wound.

[B]

I mean, you know, wildlife or cows aside, screwworms will happily lay their eggs in pretty much any warm blooded animal, including humans.

[D]

And it can be a pretty small wound, like as small as a little cut or a bite on the skin.

[B]

I read that they can also get in through just like bodily openings. Is that true?

[D]

It is true. They are often attracted to mucous membranes. So eyes, nose, ears, urogenital. Yikes. So yes. And during this outbreak, there have been over 1000 human cases and the number continues to grow daily.

[B]

And to be fair, not to fear monger here, this is not a pandemic level human health crisis. Most people that take precaut will be totally fine.

[D]

But I also think very much about this on an individual level.

[B]

And the kinds of individuals that would be the most susceptible to a serious screwworm infestation, like folks who can't get medical help right away, or people who are unhoused or have weakened immune systems, or even like kids with a lot

[D]

of scrapes, they're the last ones that need to deal with something like this.

[B]

And on the off chance that it does happen, it is kind of a horror show.

[D]

One of the most impactful images that I have seen related to 2020 patients that were lining the hallway of a medical treatment facility in a country that is currently part of this outbreak. And the patient was holding a bowl in which they were basically sneezing out and pushing out larvae from their nasal passage. And other people who were lining this hallway basically waiting to be seen because they were also needing to get the maggots out of their body.

[B]

Oh my gosh. Okay.

[A]

All right. I, I now I see the point that this is more than just the cattle industry.

[D]

Yeah.

[A]

But I do now wonder if it's just gonna keep coming back. Like, is this just an inevitable cycle that we're now stuck in? Like we're just gonna have to keep doing this. Yeah.

[E]

You kind of are on a treadmill. You're on a treadmill using nippling's technique. Yeah.

[B]

But I did, as I was reporting on this, come across a different way that people are starting to think about screwworm control.

[E]

So another option that is controversial, but scientists have been talking about it.

[B]

This is something that Sam mentioned too,

[E]

is something called a gene drive.

[A]

Okay, so what is that?

[E]

It kind of goes around the normal mendelian laws of genetics.

[B]

Okay. So first of all, let's assume that you are a scientist that has modern day genetic technology is available to you. And you introduce a killing gene into the screwworm population, you could make it

[E]

lethal to be a female. So it could trigger something where females just don't get out of the egg stage.

[A]

It's like a little time bomb in the cell.

[B]

Yeah, exactly. And typically, if you were to try to do that, genetics would work its normal way, and that killing gene would only get inherited 50% of the time, and in every successive generation, it would become less and less common, and you'd have to keep reseeding that gene into the population. Okay, but this is where gene drives have a little extra trick.

[E]

In a gene drive, there's closer to 100% chance that the gene will get passed down.

[B]

You can basically ensure that it'll get passed down every time. And so it's kind of like a set it and forget it kind of thing. Like, you introduce the killing gene and then you just let it have its way. With the screwworm population, the screwworm's gonna

[E]

be out there reproducing and spreading by themselves very quickly.

[B]

And what that really means is eventually

[E]

it's gonna wipe them out.

[B]

Not just, you know, beating screwworms back down to Panama, but, like, truly and wholly eradicating screwworms.

[A]

Extincting them off of.

[B]

Extincting them off the face of the planet forever.

[A]

I just, like, I. I don't want us to have to live with these, but I don't want us to kill them forever. That feels wrong. That feels like we untake. Backable. That is not that we should not be doing.

[B]

Yeah, yeah. So, I mean, but let me bring in one more person here.

[F]

So I'm Greg Kapenick. I am a research scholar at the

[B]

Hastings center, because I think he feels a lot of the same way.

[F]

I mean, here we are in the early stages of the sixth major extinction, one that we humans are causing. And I mean, in a way, this seems like, gosh, joining forces with the other side in some way.

[A]

Yes, yes, exactly.

[B]

Well, but at the same time, Gregory has seen this potential use of gene drives coming on the horizon and really wanted to think about it more. So what he decided to do is get together a panel.

[F]

I thought I'll turn to some environmental

[B]

ethicists, ecologists, conservation biologists, geneticists, entomologists, some

[F]

people with public health background.

[B]

No one from the Texas Cattle Ranchers Association.

[A]

We already know what they say.

[F]

I thought it would be particularly interesting to bring together people who would be, by and large, kind of predisposed to want not to take out species. So we gathered at Arizona state in May 2024. For a day and a half of presentations and discussion, they considered a couple

[B]

of the top nasty species, like the

[F]

mosquito species that is the main vector

[B]

of malaria, and one of them was screwworms.

[F]

Mm.

[B]

So the idea was to hash out some of the pros and cons for either side.

[F]

You know, keep, eliminate, and sort of report out our findings.

[B]

And given the group of people that were sitting at the table, they started out with some of the arguments that you might expect.

[F]

We need to think about the value of species.

[B]

Yeah. What do you mean when you say that?

[F]

Yeah, I mean, there'd be different ways in which a species could be valuable.

[B]

Like, first off, there's some very practical ecological considerations.

[F]

I mean, the main question is, what's it doing in the wild? Is it a pollinator? Turns out screwworm is something of a pollinator.

[B]

Is it?

[F]

Yeah, it is.

[B]

Oh, my gosh.

[F]

Yeah. But it's probably not a very important pollinator.

[B]

Okay.

[F]

There are a lot.

[B]

Bees do it better.

[F]

Yeah, the bees probably win.

[B]

Then you have to consider whether some other animal needs to eat it.

[F]

Probably sometimes.

[B]

But turns out it's not really a key food source for any other animal.

[F]

Does it play an important role as a predator and keeping other species in check?

[B]

I mean, obviously, in this case, yes, it is a predator, but according to Gregory, the animals it eats are already

[F]

under pressure from human forces. So if anything, you want to ease the burden as much as you can on those species.

[B]

Okay. But they did also consider some more abstract values that a species might have.

[F]

You know, aesthetic. Aesthetic, educational, historical, scientific. I think that's the list.

[B]

Or maybe we put it in terms of screwworm.

[A]

Yeah. In my mind, I was thinking about it, like, if you were going around the way you did, and you opened it up to all your colleagues, and then sitting there was a giant screwworm who was gonna make the case to save itself. Yeah. Like, what's the best case that that screwworm would make?

[F]

That's the hard case.

[A]

Aesthetic, clearly.

[B]

Right.

[E]

Educational.

[F]

Like, don't mess with nature, kids.

[B]

You know, jokes aside, though, I mean, Gregory says, you know, people like him do actually put a lot of stock in the sort of intrinsic value of a species.

[F]

It's this ingenious development in and of its own. Right.

[B]

You know, anything that's around today has been honed by millennia of evolution. And in that way, every species is

[F]

a marker of the creative natural forces that sustain life that brought us into being. I mean, I feel like you have to try to put it in a practically poetic way in order to really convey what people are thinking.

[B]

So Gregory's group, after about a day and a half of discussing all of

[F]

this, we're all kind of exhausted, and we're trying to, like, put it all together.

[B]

And Gregory says, okay, we're gonna go around the room one by one, sort of put.

[F]

Put everyone on the spot and see what they thought. And we did.

[B]

So.

[F]

And by the time we'd gone around, everyone had. Most people had. I think maybe everyone had actually said, yeah, screwworm looks like a pretty good candidate, really,

[A]

that it would be okay to wipe this species off the planet forever.

[F]

Yeah.

[B]

How did that feel? Is that awkward?

[F]

Well, I mean, it was this, like. It was kind of like this serious moment. There was. Everyone was sort of sighing for us. We're like, oh, I really don't want to. I really don't want to vote for this, but. But it looks like maybe the case can sometimes be strong enough.

[A]

But isn't there sort of like. I mean, this just feels like, you know, an idea that always comes up with ecosystems. Like, we think we know and then we don't. Like, there's always the knock on effects that we never see coming. And we thought we knew everything, but then it surprises us, but there it is. Like, does it not feel like hubris to assume that we know everything that could potentially go wrong?

[F]

Yeah, but we did, in fact, at least up until very recently, get rid of screwworm in southern North America and throughout Central America. And, you know, the sky didn't fall, other species didn't wink out because they weren't able to eat New World screwworm anymore. So we have a little bit of a kind of preliminary, like, experimental data. Yeah, kind of like that suggests that it's probably not really that important ecologically.

[B]

So losing it, you know, doesn't seem to do any harm. And then on the other side, part

[F]

of what was so persuasive about it was that the death that it causes is exquisitely awful.

[B]

I mean, with screwworms, did you guys consider alternatives to eradication?

[F]

Like, if there were some other kind of treatment for it, some sort of medicine that you could take?

[B]

Gregory says if it was possible to, like, separate screwworms from the thing that they do or, like, the disease that they cause of, you know, flesh being eaten, and you. If you could attack that disease, then great. You know, like, that's sort of the case with malaria and mosquitoes, where you can. You can attack the disease or in that case, the parasite rather than the mosquito. But with screwworms, there's just no way to do that. Like, eating flesh is in their nature. It's what they do. There's just no way to make them, like, veget vegetarians or make them uninterested in flesh.

[F]

The only way you get rid of the disease is by getting rid of the fly. At least at the time that we were meeting and writing, there was nothing else to do except take it out if you can eliminate the flies.

[A]

I don't know. I don't know. I want to agree with him, but I, I, I just, I don't know if that wins the day for me. Like, I'm. I don't disagree, but I just can't bring myself to agree.

[B]

No, this is, you know, this is the part of the story where I feel like I agree. I don't know. I don't know what to do with the fact that I don't want screw worms to exist. You know, Like, I think about, like, the people in South America. We just stopped at Panama. I don't know. I don't want them to have to deal with screwworms and suffer and. But at the same time, this stuff gets scary, I guess. One thing I will say, though, that Gregory did mention is that that if we go down this path, theoretically there is sort of an undo button here.

[F]

You can definitely keep it somewhere else in a facility or, you know, frozen eggs or something. And if it were to turn out

[B]

that, like, the cure for cancer was in the screwworm eggs or really vital

[F]

to the life cycle of this frog species in South America or something like

[B]

that, some ecological brute Goldberg machine got set off because we got rid of all the screwworms.

[A]

Yeah.

[F]

It would be possible to achieve something like de extinction with screwworm to bring

[A]

it back to seed it, fling it out of the plains the way we're flinging out the sterile ones.

[B]

Yeah.

[F]

And what we know from the outbreak in Central America now is that they can take off pretty well.

[A]

Imagine the, like public campaign where it would be like, hey, everybody, remember how we remember how we remember how they used to exist? There's this one frog in Panama that this was really helpful for. So we're just gonna drop these flesh eating worms. We're just gonna rain them down over you and your home.

[B]

Yeah.

[A]

So one last thing before we go back. In 2016, Edward Nipling and his screwworm research won a Golden Goose award. If you haven't heard of it before, the Golden Goose award goes to US Government funded science that sounds ridiculous but ends up changing the world. And Nippling's research was exactly that. Even years after it proved useful, members of Congress still ridiculed and scapegoated it.

[E]

Frivolous pork projects such as the Screwworm

[A]

Research $35 million as an example of government waste.

[F]

Even though the screwworm has been eradicated

[A]

in the United States, this is now the fourth Golden Goose inspired story that we have done nice. We did one about cone snails called Golden Goose, one about a bacterium called the Age of Aquaticus, and one recently about honeybees called Time is Honey. And now this one. It's almost become like a sneaky little recurring series that if you ever meet someone who doesn't believe that the government should fund basic science, just one of these. We'll link them all in the Episode Description

[B]

this episode was reported and produced by me, Sara Khari, with reporting help from Latif Nasser. Our fact checker was Emily Krieger. Check out Sam Keane's podcast the Disappearing Spoon. His episode about screwworms is linked in our episode description. Same goes for Sarah Zhang's latest story in the Atlantic. And if you are interested in hearing more about gene drives, check out our episode about it. The last 10 minutes of our CRISPR update.

[A]

Thank you to James P. Collins, Max Scott, Amy Mario, Daniel Griffin, Phil Kaufman, Katie Barnhill, Arthur Kaplan, Ron Sandler, Yasha Roher, and our gaggle of friends at AAAS who administer the Golden Goose Award, Erin Heath, Gwendolyn Bogard, Valerie Sabate, Meredith Asbury and Joanne Padrone Carney.

[B]

And last last thing. If you want more information on screwworm infested areas or how you can take precautions to be safe, there is a website you can check out.

[A]

It is screwworm.gov that's screwworm.gov Sara I guess it's time for us to just screw off. Indeed, and we'll catch you next week.

[B]

Hi, I'm gabby.

[C]

I'm from san francisco and here are the staff credits. Radiolab is hosted by lula miller and latif nasser. Soren wheeler is our executive editor. Sarah sandbach is our executive director. Our managing editor is pat walters. Dylan keefe is our director of sound design. Our staff includes jeremy bloom, w. Harry fortuna, david gable, maria paz gutierrez, sindhu nainasenbandan, matt kielty, mona mcgacher, annie mckeown, alex neeson, sara kari, rebecca rand, anisa

[B]

vitse, arian wack, molly webster, and jessica

[C]

young, with help from gabby santis.

[B]

Our fact checkers are diane kelly, emily

[C]

krieger, natalie middleton, angeli mercado, and sophie semester. Leadership support for Radiolab's science programming is provided by the Simons foundation and the John Templeton Foundation.

[B]

Foundational support for Radiolab was provided by

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