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Return of the Screwworms

42m 29s

Return of the Screwworms

A flesh-eating insect known as the New World screw worm, long eradicated from North America, has made a dramatic comeback in Central America, spreading northward and now within 300 miles of the U.S. border. This resurgence, first noticed in the Florida Keys in 2016, traces back to a groundbreaking 1950s strategy developed by entomologist Dr. Edward Nippling. His approach—releasing mass quantities of sterile male screw worms to outcompete breeding pairs—successfully eliminated the pest across the Americas by the 2000s, establishing a continent-wide biological barrier. Today, however, the resurgence is prompting urgent questions about the ethics of species eradication. Scientists now debate whether tools like gene drives—engineered to spread a lethal gene through populations—could permanently eliminate the pest, even if it means removing a species with ecological and intrinsic value. A panel of environmental ethicists found that while screw worms are not ecologically vital, their devastating impact on animals and humans, including over 1,000 human cases linked to wounds, makes eradication seem justifiable. Still, concerns remain about unintended ecological consequences and the hubris of assuming full control over nature. The story underscores a broader dilemma: as humanity faces its sixth mass extinction, should we use science to eliminate harmful species—even if it feels morally wrong? The case of the screw worm illustrates both the power of basic science and the deep ethical tensions that arise when science intersects with nature. The U.S. government and public health agencies are now actively responding, with increased research, border patrols, and new sterile fly factories being built. The controversy highlights a recurring theme in science: innovations that once seemed absurd—like screw worm control—can transform ecosystems, but their long-term implications remain deeply uncertain.

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- Wait, you're listening. - Okay. - Come on. - Okay. - Come on. (clears throat) - Dordless. - Listening. - To Radio Lab. - Radio Lab. - From WNYC. - To C. - To C. - Yeah. - Hey, I'm Latif. This is Radio Lab. And today, I have with me, Osara. - Okay, no echo or anything? - No. - Okay, great. - As in Radio Lab reporter producer, Sara Cari. - Can you hear me without an echo? - Oh, yeah, no. You sound great. - And? - Sara's here in the studio. - I have a Sara. - Hello. - Hi. - Hi. - Nice to talk to you. - Sara Zane, 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 ozemic. - 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 even 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. - You need a very grave situation for this endangered key. - People suddenly saw her noticing that all these like ugly, like gristly wounds on these deer. - Gaping holes or wounds in their neck or in their in their head. - Literally you could see down to the bone. - Ruse, 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. - But 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. I also know that it's flesh-eating worm. - Oh. - Then like I had never heard about screw worms before. - Yeah, no. - I would imagine most Americans have never heard about screw worms before. And the reason we don't know about it is because it's been eradicated from our country. - Huh. - And it's like, what? That's crazy. I've never heard of like an insect being like completely eradicated from our country. - And 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 screw worm 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 Keene. - My name is Sam Keene. I am a science writer. Because it turns out he, like Sarah, at some point had fallen into the screw worm hole. 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, let this, when we first learned about this, I got obsessed and started doing some dating and learned that Nippling has unfortunately passed away. - But. - 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, like in Texas, March 20th, 1999. - Nippling grew up on his family farm in Texas. - And. - No days farming was a very difficult occupation. - Honestly, mostly because of the, what was this supposed to say after that? - Discruer. - Oh, mostly because of screw worms. - Yeah, so it was a problem for ranchers. Actually, I think this is a quote I remember. It was, screw worms used to strike fear in the hearts of ranchers all throughout 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? Your 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, making 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 the 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. - Oh, yeah, it's, (laughs) - And they are extremely hard to get out once they have locked in. - A screw worm would get into the table of calves when they were born or-- - 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. (laughs) - Have to try to yank them out of these animals that obviously aren't happy about this. - Is there a tool you use? Like what are you guessing at tweezers or just fingers? - Screw driver, you gotta 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. - 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 pole weave. And ton of us and cue legs. - 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 screw worm. I want to put a stop to them somehow. - And as it happens. - The first job I had-- - In the late thirties, he got a job at the USDA. - As an entomologist working on this screw worm, it was the Bureau of Entomology and Planned Quarantine at that time. - And then-- (thunder rumbling) - Rule board two breaks out. - And the military enlists him in developing-- - An insecticides and repellents for use by the-- for the own purpose. - He actually ends up helping develop DDT. - So, yeah, part 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 me, right? - So after the war, when he gets back to his screw worm 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 screw worms mate. Just watching love insect sex. - As one does, like, well, yeah, why, why? - I think he was just trying to understand these tests, right? I think, like, what could we do about it? - And so one day, a colleague of nipplings is, you know, watching the screw worms 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 it. - 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 you could just do something to all of the males, right? Like, if you could just make the male sterile. - And then if you could trick the female screw worms into mating with these sterile males, the females aren't gonna lay in the egg, so they're viable. - That would essentially take those females out of circulation for reproduction purposes. - Their one shot would just be doomed to fail, basically. - Yes, exactly. - So just 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 screw worm 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, 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 and x-rays. - And I think he sort of jumped off of his couch and said, "Oh my God." "Maybe we could start last rumor." Like this could be the solution to the problem. Okay, so what is he, 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 that. I mean, remember, he's working for the government. Like tax pair of monies, that's take here. What happens if the press gets a hold of this and then we're just told they ridicule the fur like, "Watching money, or watching insects all the time." Not in a weird way. Yeah. So 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. Flush eating worms in a hospital. 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 like hanging out the loading dock at night and like grabbing the door right before it shots or like water gate like 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 clandestined about it, sneak around a little bit. And they're literally like, you know, putting these flies through the next machine and be like, "Hey, what happens?" But the problem is shooting a bunch of radiation and 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 kind of a problem. 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 Island. He shows up there with some of the radiated screw worms from his lab. It releases them on the island. And it did not work. Like the population of screw worms stayed pretty much the same. The experiment failed. And Nippling was glad he hadn't said anything or 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 striving 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? Off the coast of Venezuela. He wrote letters. 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 a 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 two few flies. Like no more handful of flies from his rinky-ding lab. They were 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 that they get putrid and then they would douse it with formaldehyde. And it was cheap enough to get, you know, so they knew they could produce a lot of this stuff pretty quickly. Okay. Are they formaldehyde? I don't know. Yeah. Apparently they just like the formaldehyde. I don't know. It's just a little extra kick. It's like hot sauce for them. 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. Only livestock people especially. Ranchers catch hold of this. They came to us. And they're like, wait, we really want this. And 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 US, and so armed with some funding from the USDA. This new technique for insect control is eliminating screwworms. 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 cattleman's association hears about it. I mean, it was a Texas size problem that they had. They wanted to, so nippling and his team. And up building a really big factory in Texas. Screwworm eradication headquarters, admission Texas, here millions of screwworm flies are being reed 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 piece of a life cycle. So imagine it smelled good. I'm sorry to say this, but what it reminded me of was the smell of a used tampon. OK. It makes sense. Well, that's kind of 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 screwworm flies in mission Texas. Basically, they were flying through the sole like prop planes and released 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 were really going to deal with this trueworm problem, we would have to enlarge the program. What if we just kept going? This operation can now expand into Mexico. 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 were 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 screwworm 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 in like, there are still, there's a still a factory in Panama. It's still producing millions of squirms, growing millions of squirms 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. The idea is that that area where Panama meets Colombia, the jargon gap, which I think it's been the use of a lot for other reasons. That's like the most dangerous area for migrants, right? Exactly. But it's also one of the narrowest parts of the Americas, only about 60 miles wide. Okay. So it's like a natural choke point. Right. And because of that, maintaining that sterile screwworm barrier only costs. $15 million per year, which is a pretty reasonable price compared to the huge cost if squirms were just kind of running wild. Yeah. So when I was praying on this back in 2020, the money saved was estimated to be over $1 billion per year. So a billion dollars saved compared to 15 million cost. Wow. So that's a pretty good return. And obviously it was more expensive when you were, you know, in the active eradication phase. Right. But the maintenance cost, you know, is really not that much money for a government program. It's just a kind of 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 screwworms meet in the lab and having an epiphany is kind of remarkable. Right. Now, there have been a couple of small outbreaks here and there over the years, including the Florida one, the gear, right 2016 one, yeah, but they've all gotten tammed 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 going to break loose. News, biological barriers, and maybe also lots of heart. This is Radio Lab, I'm Lutthifnasser, here with producer Sara Cari. Hello. And we've been talking to journalist Sara Zhang and writer Sam Keene about screw worms. Right. The skin-crawly, flesh-eating parasite that we all forgot about because nippling and hysterylflies drove it down south. All the way to a biological demilitarized zone at the very bottom of North America, a.k.a. the southern border of Panama. Yeah. But in 2023, we now have a new brother, a new brother. Panama suddenly started seeing a massive spike in screw worm cases from like 25 cases a year to like thousands. And since then, it's only gotten worse. The parasitic fly is moving north. They have been steadily marching north. They've been found in Costa Rica, Honduras, El Salvador, Guatemala, even in Mexico. Only 700 miles from the U.S. border. And it turns out it's basically getting closer every day. Less than 400 miles, 300 miles from Texas on the southern border. It's gotten as close as 70 miles or so from the U.S. border. Whoa. This is an ongoing breaking new story. So what happened, like how did they get past the biological wall? There are a couple of theories. One theory is that maybe the strain of screw-in that they were growing in the factory was not as effective anymore. And maybe the ladies out there caught onto what was going on and weren't mating with them or something. Yeah. Just general disruptions due to COVID might have weakened the production a little bit. Or maybe Sam says, given that we live in a more and more interconnected world, because it does still exist in 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. The best guess is that people were smuggling cattle that were infected, and then it just got out. But, regardless, as of today, right now, the screw worm, it's sort of like knocking on our doorstep. It's not a matter of if the deadly pest gets to the U.S. but when. 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. The issue has also alarmed Washington. It actually does seem like the U.S. government is paying attention. The U.S. Department of Agriculture has snapped into action. And really, just like Nippling's time, pretty much because of the cattle industry. Billions of dollars of losses a year. Of course. They really crush the cattle industry as well as other livestock industry in Texas. So, the USDA has started to set up screw worm traps along the U.S. Mexico border. Cut down the southern border. They have agents on horseback. These are so-called tick riders. Patrolling the border for stray cows, they are pouring money into screw worm research. And of course, they are rebuilding Nippling's fly factories. They are now building a new facility down in Texas. They're one in Mexico, all told probably in the next couple years, we will be producing and releasing something like 500 newyan flies per week. Wow. And we probably will have spent like hundreds and hundreds of millions of dollars. Do you see this as like the modern cow factory form system is like unsustainable? And like this is just like one other bandaid to keep that system financially profitable. So, like I could see an argument that's like, oh, this is just to help like big rancher businesses. Yeah. Well, I think 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 even argue with that premise, but this does affect wild animals too. Right. In Central America, like used to see like howl or monkeys fall out of trees because they had become so just figured and sick from getting infested by school worms. 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. So I'll try and make the case on the human side of things. Number one. So I talked to this public health official named Megan Nichols, who is at the CDC. And my current role is incident manager for our new world screw worm response, because the CDC is worried about this outbreak too. And the thing that Megan pointed out is that these flies like to infest a wound. I mean, you know, wildlife or cows aside, screw worms will happily lay their eggs in pretty much any warm blooded animal, including humans. And it can be a pretty small wound, like as small as a little cut or a bite on the skin. I read that they can also get in through just like bodily openings. Is that true? It is true. They are often attracted to mucus membranes. So eyes, nose, ears, your genitals. Yeah. So yes. And during this outbreak, there have been over 1,000 human cases. And the number continues to grow daily. And to be fair, you know, like not to fear monger here. This is not a pandemic level human health crisis. Most people that take precautions will be totally fine. But I also think very much about this on an individual level and the kinds of individuals that would be the most susceptible to a serious screw worm 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 of scrapes. They're the last ones that need to deal with something like this. And on the off-chance that it does happen, it is kind of a horror show. One of the most impactful images that I have seen related to 2025 was 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. Oh my gosh. Okay, all right, I now see the point that this is more than just the cattle industry. But I do now wonder if it's just going to keep coming back. Like is this just an inevitable cycle that we're now stuck in? Like, we're just going to have to keep doing this. Yeah, you kind of are on a treadmill. You're on a treadmill. Yeah. Using Nippling's technique. Yeah. But I did, as I was reporting on this, come across a different way that people are starting to think about screw room control. So another option that is controversial, but scientists have been talking about it. This is something that Sam mentioned too. It's something called a gene drive. Okay. So what is that? It kind of goes around the normal Mendelian laws of genetics. Okay. So first of all, let's assume that you are a scientist that has modern day genetic technologies available to you and you introduce a killing gene into the screw room population. You could make it lethal to be a female, so it could trigger something where females just don't get out of the egg stage. It's like a little time bomb in the cell. 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 receding that gene into the population. But this is where gene drives have a little extra trick. In a gene drive, there's closer to 100% chance that the gene will get passed down. 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 screw room population. The screw rooms are going to be out there reproducing and spreading that gene by themselves very quickly. And what that really means is eventually, it's going to wipe them out. Not just, you know, beating screw worms back down to Panama, but like truly and wholly eradicating screw worms. Extincting. Extincting them off the face of the planet forever. I just, well, 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're doing something untick backable that is not, that we should not be doing. Yeah. Yeah. So I mean, but let me bring in one more person here. So I'm Greg Cape Nick. I am a research scholar and the Hastings Center, because I think he feels a lot of the same way. 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. Yes. Yes, exactly. 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. I thought I'll turn to some environmental ethicists, ecologists, conservation biologists, geneticists, entomologists, some people with public health background, no one from the Texas Cattle Ranchers Association. We already know what they think. 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 of the top nasty species like the mosquito species that is the main vector of malaria and one of them was screw worms. Yes. So the idea was to hash out some of the pros and cons for either side, you know, keep eliminate and sort of report out our findings. And given the group of people that were sitting at the table, they started out with some of the arguments that you might expect. We need to think about the value of species. Yeah, what do you mean when you say that? Yeah, I mean, there'd be a different ways in which a species could be valuable. Like first off, there's some very practical ecological considerations. I mean, the main question is, what's it doing in the wild? You know, is it a pollinator? Turns out screw worm is something of a pollinator. Is it? Yeah, it is. Oh my gosh. Yeah. But it's probably not a very important pollinator. Okay. There are a lot. The bees do it better. Yeah. The bees probably win. But you have to consider whether some other animal needs to eat it. Probably sometimes. But turns out it's not really a key food source for any other animal. Is it? Does it play an important role as a predator in keeping other species in check? I mean, obviously in this case, yes, it is a predator. But according to Gregory, the animals it eats are already under pressure from human forces. So if anything, you want to ease the burden as much as you can on those species. Okay. But they did also consider some more abstract values that a species might have. You know, aesthetic. Eesthetic. Interesting. Educational, historical, scientific. I think that's the list. Or maybe we put in terms of screw worm. 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 screw worm who is going to make the case to save itself. Yeah. Like, what's the best case that that screw worm would make? That's the hard case. Eesthetic. Clearly. Educational. Like don't mess with nature kids. 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. It's this ingenious development in and of its own right. You know, anything that's around today has been honed by millennia of evolution. And in that way, every species is 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. So Gregory's group after about a day and a half of discussing all of this. We're all kind of exhausted and we're trying to like put it all together. And Gregory says, okay, we're going to go around the room one by one. Sort of put everyone on the spot and see what they thought. And we did so and by the time we'd gone around, everyone that most people had, I think maybe everyone had actually said, yeah, screw worm, looks like a pretty good candidate. Really? Like that it would be okay to wipe this species off the planet forever. Yeah. How did that feel? Is that awkward? Well, I mean, it was just like, it was kind of like this serious moment. It was everyone was sort of sighing, sort of like, oh, I really don't want to vote for this, but it looks like maybe the case can sometimes be strong enough. But isn't there sort of like, I mean, this just feels like, you know, an idea that always comes out 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? Yeah, but we did in fact, at least up until very recently, get rid of screw worm 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 screw worm 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. So losing it, you know, doesn't seem to do any harm. And then on the other side part of what was so persuasive about it was that the death that it causes is exquisitely awful. I mean, with screw worms, did you guys consider alternatives to eradication? Like if there were some other kind of treatment for it, some sort of medicine that you could take. Gregory says, if it was possible to like separate screw worms 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 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 screw worms, 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 vegetarians or make them uninterested in flesh. 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. Oh, I don't know, I don't know. I want to agree with him, but I just, I don't know if that wins the day for me. Like I don't disagree, but I just can't bring myself to agree. You know, this is, you know, this is the part of the story where I feel like I agree with you. 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, like, I don't know. I don't want them to have to deal with screw worms and suffer. But at the same time, this stuff gets scary. I guess one thing I will say, though, that Gregory did mention is that if we go down this path, theoretically, there is sort of an undue button here. You can definitely keep it somewhere else in a facility or, you know, frozen eggs or something. And if it were to turn out that like the cure for cancer was in the screw worm eggs or really vital to the life cycle of this frog species in South America or something like that. Some ecological group Goldberg machine got set off because we got rid of all the screw worms. Yeah. It would be possible to achieve something like the extinction with screw worms. To bring it back to seed it, fling it out of the planes the way we're flinging out the sterile ones. Yeah. And what we know from the outbreak in Central America now is that they can take off pretty well. Imagine the like public campaign where it would be like, hey everybody, remember how we remember how we remember how they used to exist. Right. There's this one frog in Panama that this was really helpful for. So we're just going to drop these flesh eating worms, uh, we're just going to rain them down over you and your home. Yeah. So one last thing before we go back in 2016 Edward Nippling and his screw worm research won a Golden Goose Award. If you haven't heard of it before, the Golden Goose Award goes to U.S. 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. Frivolous pork projects such as the screw worm research, $35 million as an example of government waste. Even though the screw worm has been eradicated in the United States. This is now the fourth Golden Goose inspired story that we have done. We did one about cone snails called Golden Goose, one about a bacterium called the Age of Aquaticus and one recently about honey bees 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 play them one of these. We'll link them all in the episode description. and produced by me, Sarah Carrey, with Reporting Help from Lotha Fnasser. Our fact checker was Emily Krieger. Check out Sam Keane's podcast, The Disappearing Spoon. His episode about screw worms is linked in our episode description. Sam goes for Sarah Zang'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. - Thank you, too. James P. Collins, Max Scott, Amy Moreo, Daniel Griffin, Phil Kaufman, Katie Barnhill, Arthur Kaplan, Ron Sandler, Yasha Roer, and our gaggle of friends at Triple A.S. who administer the Golden Goose Award, Aaron Heath, Gwendolyn Bogart, Valerius Sabate, Meredith Azbrie, and Joanne Padrone. - And the last last thing, if you want more information on screw worm infested areas, or how you can take precautions to be safe, there is a website you can check out. It is screwworm.gov. - That's screwworm.gov. Sorry, I guess it's time for us to just screw off. (laughs) - Indies. - And we'll catch you next week. - All right. (upbeat music) - Hi, I'm Gabby. I'm from San Francisco, and here are the staff credits. Radiolab is hosted by Lula Miller and Lethifnossar. 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, Sindu Nainisambandan, Matt Kielte, Mona McGawker, Annie McEwan, Alex Nason, Sara Kari, Rebecca Rand, Anisevica, Aryan Wack, Molly Webster, and Jessica Young, with help from Gabby Santas. Our fact checkers are Diane Kelly, Emily Krieger, Natalie Middleton, Angelie Mercado, and Sophie Semi. Leadership support for Radiolab's science programming is provided by the Simon's Foundation and the John Templeton Foundation. Foundational support for Radiolab was provided by the Alfred P. Sloan Foundation. [BLANK_AUDIO]

Podcast Summary

Key Points:

  1. The New World screw worm, a flesh-eating parasite, resurged in Central America in 2023, moving northward and now threatening the U.S. border after decades of eradication.
  2. The eradication effort pioneered by Dr. Edward Nippling in the 1950s used sterile male flies released via airplanes, successfully eliminating screw worms across North and Central America by 2006.
  3. The reemergence of the pest has sparked ethical debates about whether humanity should deliberately eradicate species, with scientists and ethicists weighing ecological, moral, and practical concerns about extinction via gene drives.

Summary:

S. border. This resurgence, first noticed in the Florida Keys in 2016, traces back to a groundbreaking 1950s strategy developed by entomologist Dr.

Edward Nippling. His approach—releasing mass quantities of sterile male screw worms to outcompete breeding pairs—successfully eliminated the pest across the Americas by the 2000s, establishing a continent-wide biological barrier. Today, however, the resurgence is prompting urgent questions about the ethics of species eradication.

Scientists now debate whether tools like gene drives—engineered to spread a lethal gene through populations—could permanently eliminate the pest, even if it means removing a species with ecological and intrinsic value. A panel of environmental ethicists found that while screw worms are not ecologically vital, their devastating impact on animals and humans, including over 1,000 human cases linked to wounds, makes eradication seem justifiable. Still, concerns remain about unintended ecological consequences and the hubris of assuming full control over nature.

The story underscores a broader dilemma: as humanity faces its sixth mass extinction, should we use science to eliminate harmful species—even if it feels morally wrong? The case of the screw worm illustrates both the power of basic science and the deep ethical tensions that arise when science intersects with nature. S.

government and public health agencies are now actively responding, with increased research, border patrols, and new sterile fly factories being built. The controversy highlights a recurring theme in science: innovations that once seemed absurd—like screw worm control—can transform ecosystems, but their long-term implications remain deeply uncertain.

FAQs

The New World screw worm is a flesh-eating fly whose larvae burrow into wounds and consume living tissue, creating painful, gaping wounds. It is considered one of the worst parasites due to its ability to rapidly destroy flesh and the difficulty of removing the larvae once they have established.

In the 1950s, entomologist Dr. Edward Nippling developed a mass-release strategy using radiation-sterilized male screw worms. These sterile males were released in large numbers to mate with wild females, preventing reproduction. This method successfully eliminated screw worms from the U.S. and much of Central America by the 2000s.

The systematic release of sterile male screw worms disrupted the reproductive cycle of the population. Over time, this led to a dramatic decline in the wild populations, and by 2006, North America was declared screwworm-free, thanks to coordinated international efforts and sustained implementation of the strategy.

Yes, screw worms have made a resurgence, with outbreaks reported in Central America, including Costa Rica, Honduras, and Mexico, and now within 300 miles of the U.S. border. This resurgence is concerning as it threatens to cross into the U.S. cattle and human populations.

Yes, screw worms can infest humans through small wounds, bites, or mucous membranes like the eyes, nose, or genitals. Since 2023, over 1,000 human cases have been reported, with severe cases involving painful, flesh-eating infestations that require medical intervention.

A gene drive is a genetic technology that ensures a specific gene is passed on to nearly all offspring, allowing it to spread rapidly through a population. Scientists have proposed using it to introduce a lethal gene into screw worm populations, potentially eradicating them permanently.

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