Chapter 1: What was the historical impact of the screwworm in North America?
Hey, I'm Latif, this is Radiolab, and today I have with me... A Sarah. Okay, no echo or anything? Nope. Okay, great. As in Radiolab reporter producer Sarah Khari. Can you hear me without an echo? Oh, yeah, no, you sound great. And... Sarah's here in the studio. I have a Sarah. Hello. Hi. Hi, nice to talk to you.
Sarah Zhang, who writes for The Atlantic and is a wildly prolific science journalist. Oh, thank you. Like, I feel like you cover COVID. I know you cover autoimmune diseases. I know you cover Ozempic. I'm sort of lucky enough to cover just like whatever I'm interested in. But we called her up because a while back, she noticed something weird happening to the deer in the Florida Keys.
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. Okay. And so back in 2016. A very grave situation for this endangered key deer. People suddenly started noticing all these like ugly, like gristly wounds on these deer. Gaping holes or wounds in their neck or in their head.
Literally, you could see down to the bone. Gruesome, painful. It's a very sad sight. So it was, you know, it was kind of like a weird thing happening in Florida story. Yeah. Volunteers are teaming up to treat affected animals. What it turned out was that There was an infestation of an insect called the New World Screw Worm. New World Screw Worm? The New World Screw Worm.
Also known as flesh-eating worm. Oh.
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Chapter 2: How did Edward F. Knipling contribute to screwworm eradication?
And like I had never heard about squirrel worms before. Yeah, me neither. I would imagine most Americans have never heard about squirrel worms before. And the reason we don't know about it is because it's been eradicated from our country. I was like, what? Like, that's crazy. I've never heard of like an insect being like completely eradicated from our country.
And as Sarah started to dig into this... It got even crazier and crazier. What she found was the kind of amazing story of one of the 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. We are on screwworm watch and we are ready.
Forcing public health officials and ranchers and ethicists. Here we are in the sixth major extinction that we humans are causing. To ask maybe one of the biggest questions that we as beings on this planet can ask. Would it ever be okay to bring about the extinction of a species? Oh, boy. Yeah. But I mean, these are about the worst parasite on Earth.
I cannot imagine anything worse than these guys. So one of the first people we called when we got into this whole screw worm thing was the author Sam Keen. My name is Sam Keen. I am a science writer. Because it turns out he, like Sarah, at some point had fallen into the screw worm hole. Yeah. I had never heard of them.
And I started Googling and then I went to Google Images and I immediately regretted doing that. And according to Sam, the reason that none of us had ever heard about what he called the worst imaginable parasite on Earth is because of something that in 1970, the New York Times called the single most original thought of the 20th century.
And it turns out that thought was born in the brain of a man named Edward Nippling. Edward Nippling. 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. Dr. Edward F. Nippling, we're happy to be here in your home today and thank you for participating in this oral history.
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. I was born in Portland, Texas, March 20, 1909. Nibling grew up on his family farm in Texas. In those days, farming was a very difficult occupation. Honestly, mostly because of the... What was I supposed to say after that? The screwworms.
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Chapter 3: What methods were used to control the screwworm population?
Oh, mostly because of screwworms. Yeah, so it was a problem for ranchers. Actually, I think this is a quote I remember. It was, screwworms used to... the Southern United States. Could we actually, could you just tell me what a screw worm even is? It is a fly. It has kind of like... Why do they call it a worm if it's a fly? Well, flies are also maggots, right? Like our flies come from maggots.
So the maggot phase is a worm. Okay, okay, okay. So basically what they do is that if you have a little like nick in your skin, a little wound... Even something as small as a tick bite? These flies would lay their eggs in those wounds. Roughly 400 eggs at a time. Oh my God. And then these maggots essentially would come out. They kind of look like a small white thread.
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 burrow themselves into the flesh like a screw. And they would eat the flesh. Ugh. Yeah, it's... And they are extremely hard to get out once they have locked in.
A screw worm would get into the navel of calves when they were born. And so back to young Edward Nippling. He got probably the worst job on the farm. which was to pick the screw worms out of the family's cows. And that was a very unpleasant task. Have to try to yank them out of these animals that obviously aren't happy about this. Is there a tool you used? I'm guessing a tweezers or just fingers.
Screwdriver. You got to use a screwdriver. That was his job. And it introduced a lifelong hatred of screw worms in his heart, you know, understandably so. But at the same time, you know, he has sort of a scientific bent of mind. He's curious. He was actually kind of fascinated by insects.
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Chapter 4: What challenges did researchers face in the screwworm eradication efforts?
Over time, he became a bug nerd. Definitely a bug nerd. Even named his cats after insects. One after a mosquito and one after a boll weevil. Antonymous and Culex. And when he grew up. Grew up to be an entomologist. But also, kind of in the back of his mind, he was always thinking, well, I have to figure out a way to control screwworm. I want to put a stop to them somehow.
And as it happens... The first job I had... In the late 30s, he got a job at the USDA. As an entomologist working on the screwworm. That was the Bureau of Entomology and Plant Quarantine at that time. And then... World War II breaks out. And the military enlists him in developing... Insecticides and repellents for use by the armed forces. He actually ends up helping develop DDT. Oh, yeah.
Heard of that one. 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. Mmm. So after the war, when he gets back to his screwworm job, he's just thinking about this problem. Like, how can we figure a way to control insects that does not require spraying lots of poisons?
And his way of trying to figure that out is watching screwworms mate. Just washing a lot of insect sex. As one does? Like, yeah, why? I think he was just trying to understand these pests, right? To think, like, what could we do about it? And so one day, a colleague of Nipling's is, you know, watching the screwworms have their sexy times, and he makes this observation.
That sounds like maybe not that important or not that interesting. But that kind of hinted at something. He wasn't quite sure what exactly. Which is that females only mate once. Whether or not they get pregnant, they get one shot to have intercourse and try to have eggs. 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. Yeah, that's it. But Nippling, he's looking at this and he's like, wait. If he could just do something to all of the males, right?
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Chapter 5: Why is the return of the screwworm a concern today?
Like, if he could just make the males sterile. And then if he could trick the female screwworms into mating with these sterile males. The females aren't going to lay any eggs. They're viable. That would essentially take those females out of circulation for reproduction purposes. Hmm. Hmm. Their one shot would just be doomed to fail, basically. Yes, exactly.
So just like somehow flood the zone with sterile males is the idea. These poor females already had it so hard and now he's just like ruining the dating pool for them. It's a little diabolical from the fly's perspective. But lucky for these screwworm ladies. It wasn't like that was a very practical idea. Because how would you even pull that off?
You know, how do you mass sterilize a bunch of insects? But then he finds a paper. An article in a scientific magazine. Basically, since World War II, there's sort of like a lot of interest in like, what can we do with radiation? Oh, of course. Right. Yeah. And this paper was by a geneticist who was saying that... It was possible to sterilize fruit flies by exposure to x-rays.
And I think he sort of jumped off of his couch and said, oh my God. Maybe we could sterilize fruit worms. This could be the solution to the problem. Okay, so what, yeah, what does he do? Well, so the thing he needs is a bunch of x-ray machines. But he decides he's not going to go public and try to get any funding for this.
We knew that if the media got a hold of that, they could make quite a deal out of this. I mean, remember, he's working for the government. Like, taxpayer money is at stake here. What happens if the press gets hold of this and then we're just totally ridiculed for, like, wishing money or something? Watching Insect Sex all the time. Not in a weird way. Yeah. We were rather cautious about that.
So he decides he wants to do this kind of on the down low. And basically he gets one of his colleagues to take a bunch of screw worms and sneak them into a nearby military hospital and use the x-ray machines there. Flesh-eating worms in a hospital.
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Chapter 6: What ethical questions arise from species extinction and control?
Great. Yeah, exactly. But how does he get the screw worms in? 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. And they are literally like, you know, putting these flies through the next machine and be like, hey, what happens? But the problem with shooting a bunch of radiation at a bunch of flies is that you create all these mutations, a bunch of random mutations. So you might just kill the fly. That's disgusting. kind of a problem.
Right. 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 flies testes are developing, right? Because that's like what you really want to knock out. So that happens to be between 5.5 and 5.7 days. So it's like they've got it to within hours. Yes. Yes. And when they do that, bingo. It seems to work.
But of course, the next thing was, would they perform in a natural population? It's not enough to just do it in a lab. So then he decides it's time for a real world test. And he found an island off Florida. On the island of Sanibel. Sanibel Island. He shows up there with some of the radiated screw worms from his lab, releases them on the island. And it did not work.
Like, the population of screwworms stayed pretty much the same. The experiment failed. And Nippling was glad he hadn't said anything or, you know, gone after public money. So, yeah, does he just resign to his failure? That's the end of the story, yeah. No, not the end of the story. We were 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. A Dutch island called Curacao. Where is Curacao?
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Chapter 7: How do gene drives offer a new approach to pest control?
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? And I thought, well, this is just the place that we're looking for. And this time, Nippling wants to go all out. They were not going to take a chance that there would be too few flies. Like, no more handful of flies from his rinky-dink lab.
They're going to set up an industrial facility for making these flies. And, like, carpet Curacao. 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. So in this factory that they set up. They came up with a formula for the food that they were going to feed them. Okay. And it was ground horse meat.
That they soaked in blood and they would let that get putrid. Wow. And then they would douse it with formaldehyde. Okay. Wow. So, yeah. And it was cheap enough to get, you know, so they knew they could produce a lot of this stuff pretty quickly. Okay. Why the formaldehyde? I don't know why. That's such a weird... Apparently, they just like the formaldehyde. I don't know. Oh, wow.
Just a little extra kick. It's like hot sauce for them. Yeah. So then from about March 1954, they are producing 170,000 of these sterile adults per week. They are feeding them this slurry, though at this point without the formaldehyde. It took 40 tons of the slurry to get that job done. Wow. 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, ranchers catch hold of this.
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Chapter 8: What lessons can we learn from the screwworm eradication story?
And they're like, wait, we really want this. Eventually, the clamor from ranchers got so big, Nippling decided, well, I think the time is right to try rolling out his screwworm strategy in the U.S. And so armed with some funding from the USDA. This new technique for insect control is eliminating screw worms. The first big push started in about 1957. In Florida.
And after about two years of dedicated work, they had eliminated them. Not just in Florida, but everywhere. East of the Mississippi. That is huge. And then it kind of keeps going west. The Texas Cattlemen's Association hears about it. I mean, it was a Texas-sized problem that they had. They won in two, so Nippling and his team. Ended up building a really big factory in Texas.
Screwworm eradication headquarters at Mission, Texas. Here millions of screwworm flies are being reared each day. All these like metal machines. Sarah told us about a similar factory she went to in her reporting. Many different rooms, sort of like all at different temperatures, different humidities for each phase of the life cycle. I could not have imagined it smelled good.
I'm sorry to say this, but what it reminded me of was the smell of a used tampon. Okay, it makes sense. blood that's gone a little bit bad, maybe. From these factories, they start releasing flies multiple times a week. So how do they do that? By airplane. These planes are being loaded with sterile male screw worm flies in Mission, Texas.
Basically, they would fly these little prop planes and release these flies in the air. 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.
And at this point... The nippling strategy is working so well, screwworms are disappearing from all of the Southwest. They started marching their way down to the border, pushing it down, pushing it down. Eventually, people were like, well, screwworms obviously don't respect national borders. If we're really going to deal with the screwworm problem, we would have to enlarge the program.
What if we just... They kept going. This operation can now expand into Mexico. You know, get them out of Mexico. Then we go down country by country through Central America. That is so much ground to cover. Yep. And so all through the 70s, 80s, 90s... There are all these kind of international agreements... Frankly, this was a tough sell in some places because the U.S.
has a history of meddling in Central America, especially in this time. But despite that, and despite political turmoil, revolutions and coups and things like that, the disgust over screwworms was enough that all seven countries in Central America came 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. And in 2006, all of North America is declared Screw worm free. Wow. And that so-called single most original thought in the 20th century changes the face of the entire continent. Amazing. And to this day, you know, at the time I was reporting it, like there are still, there's still a factory in Panama.
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