We're Screwed: Dealing with the Return of New World Screwworm

[00:00:00]Hello everyone. Welcome to Zoonosis with Joy. I'm Joy and today we're getting screwed. So, we're going to be learning about New World screwworm.

[00:00:07]We're going to learn about its life cycle, the economic damage that it does, and the recent outbreak in 2026. This video is current as of July 2026, so it's a developing story. So, if anything I say is out of date, that's why. Leave a comment, like, subscribe, share it around if you like this kind of content.

[00:00:23]Anyway, so we're specifically talking about the New World screwworm in this video. And its scientific name, I kid you not, is Cochliomyia hominivorax.

[00:00:36]Yes, that is Cochliomyia hominivorax.

[00:00:40]You can't make this stuff up.

[00:00:43]This screwworm I've talked about on this channel before in my foreign animal diseases video. Go check it out. And I feel a little bit like Cassandra because I said, "You know, if this ever gets back to America, it's going to cause billions of dollars worth of damage."

[00:00:54]And here we are in 2026 where it has reached American shores. And basically, this is a form of myiasis. Myiasis means basically, oh my gosh, my hair is sticking out like an Oompa Loompa.

[00:01:07]Anyway, there we go.

[00:01:09]>> [laughter] >> It's basically a form of a larva that will invade host tissue and infect it. So, if you've ever seen the movie Alien, this might sound very familiar.

[00:01:21]It's a little bit different than the parasitoid kind of infestation life cycle where it kills the host necessarily. Not all cases of screwworm are fatal, but many are. So, there is there is that little fun sort of thing about it, too.

[00:01:34]So, screwworm flies are pretty small.

[00:01:36]They look pretty unremarkable. And basically, when a pregnant female or a gravid female will basically look for a suitable host.

[00:01:44]Now, screwworms need a hole to screw in.

[00:01:47]And the gravid female is looking for that hole to get her little screw babies inside.

[00:01:53]So, she's going to look for an animal with an open wound. And that wound can be really anywhere. It could be on the skin, it could be on the mucous membranes, it can be inside the mouth.

[00:02:03]Uh there are cases of people and animals getting infestations inside of their mouths, and yes, in the genitalia. Uh it could be really anywhere on the body.

[00:02:11]So, to kind of demonstrate, I'm going to show you kind of visual aids that are hopefully not too, too gory, but you still get the point of what's happening here. So, first of all, you need to have that open wound. So, we're going to screw some wood here.

[00:02:23]We're practicing screwing with wood, you know, as as you do. Um this is very, you know, like you teenage years kind of stuff.

[00:02:30]Um so, once you have that kind of screw hole in there, basically, you just set your eggs around that kind of the wound edge, and that screwworm mama is going to lay lay her eggs there. Um usually, like several hundred of them, basically, just even the numbers, 100 to 300 is usually typical, but she can like lay eight like 3,000 eggs or so. So, she can do a lot of damage that way.

[00:02:51]And once they lay the eggs, basically, within a few days, those larvae are going to hatch, and they're going to start screwing into that hole, basically. And when they screw into the hole, they screw hard. Now, other like, you know, other kinds of larval infestations usually go after necrotic dead tissue, which is like black and disgusting. This is healthy tissue, basically, that they're screwing into.

[00:03:11]Um when they do that, they use their big tusks to basically dig into there. And this [clears throat] is very agonizing, so it causes a lot of pain for the animal or uh non-human, uh you know, non-human animal or human animal that it infects that way. Um so, basically, it's it's pretty nasty, and they will cause a lot of damage. Um and like I said, this could be really in any part of the body.

[00:03:33]Like, a common site in humans is actually the nasal like pharynx, basically. So, they actually get into the nose. And if you know anything about where the nose is, it's right next to the noggin. So, they can actually burrow all the way up into the brain or the meninges, basically, which is pretty horrific. Um with animals, another common site is basically any place that they do like castration or, you know, surgical stuff like docking or that kind of thing. And those larva can get into that wound and cause a whole lot of screwing, basically. So, it is something that can be really challenging to deal with that way. A common place in Texas is actually they have the Gulf Coast tick, and the Gulf Coast tick has a prevalence for the ears. So, those little tick bites can actually be a perfect site for those screwworm larva to start screwing in and causing lots of damage. So, back in the day a lot of Texas cattle used to lose their ears because of these sort of infestations.

[00:04:25]Now, after a little while those larva will typically get to a big plump size and then drop off the animal. They drop off and they bury into the soil. They pupate and then those pupa emerge into beautiful butterflies. Well, no, actually larva.

[00:04:40]Adults, sorry. The larva become adults.

[00:04:43]And the adults are flies. The female, it was discovered back in the 1930s, can only screw once. Womp womp. But the males, they are promiscuous and they screw all the time.

[00:04:56]So, the males will go around screwing as many females as they possibly can get.

[00:05:01]The female gets gravid and the life cycle starts over again. It's the circle of life. How nice. All that screwing happening on.

[00:05:08]So, basically pretty horrific. Um, but, you know, not that unusual for insects. Really what it comes down to is that this causes a huge amount of damage. You have to understand that this can affect many different animal species, not just, you know, cattle, but also horses, dogs, and humans. Those are typical and wildlife. So, deer are pretty common host species, but any kind of wildlife species that has a wound can potentially get screwwormed that way, which makes it really hard to eradicate.

[00:05:36]Um, this can cause like billions of dollars worth of damage. In fact, it was estimated that basically in 2002 that it caused well over a billion dollars worth of damage if it caused came back to uh you know, the United States is in today's money basically had to work it through the inflation calculator. That number has steadily increased with the amount of increased production that kind of thing and it causes billions of dollars worth of damage every year in South America where it still exists in in high numbers that way. So, the amount of damage this thing is incalculable. It causes a lot of economic fallout because not only does that kind of damage the skin and cause harm to the animal. I mean it damages the hide. I didn't you know, leather couches, leather seats.

[00:06:17]Where do you think that comes from? I mean, has to come from the skin of a living cow basically. Well, they usually kill it first but basically that leather has to be in good shape in order to be sellable that way.

[00:06:28]The meat, you know, they have to eat lots of grass and put that energy into bulking up and that kind of thing too.

[00:06:34]And so if the animal has a major pest infestation, it's not going to be able to put that energy there. It's going to be busy fighting off infection. So, that reduces the rate of gain, that reduces the yields, the carcass yield that way.

[00:06:46]And that can cause major economic losses for the producer. Not to mention the labor cost. Picking out all these larvae takes a long, long time. That seems to be the primary mode mode of treatment but there are kind of anti-parasiticides that we have now because leaving dead maggots in the tissue is just going to cause them to fester and can lead to you know, infection and sepsis, that kind of thing. So, typically once you get a big infestation, you have to start picking up dozens of these things from the wound that line before it becomes too much of a damage that way too. So, it was often a it was a really, really big issue like for the 8 to 10 hours a day for the summer months when this was most common, producers were like doing tons and tons of this like maggot removal and wound tending, that kind of thing especially in South Texas and Florida where it was very common. The good thing about screwworm is that it has a geographical range between about 35 degrees north and 35 degrees south.

[00:07:42]Meaning they can only really exist in places where they have kind of warm winters. It doesn't like the cold at all. Though it can have like little occasional incursions into places that are colder like northern United States or Canada. It really can't establish a range there provided climate change doesn't get too too bad and gnarly in the future. But you know, we'll have that figured out.

[00:08:03]Don't worry about it. Don't worry about it. We aren't going to get screwed by that. We're just going to have to deal with the screwworm.

[00:08:11]Anyway, [clears throat] we don't have to think about the polycrisis right now. Let's think about the screwworm.

[00:08:15]So how do we ever get the screwworm out of the United States to begin with? Well, we figured out that the males I say we a society. This guy named Nippling. Um There's lots of screwing and nippling going on here.

[00:08:32]He figured out that if you start irradiating the males, they will be sterile but they'll still have their libido. So they could still screw but they can't impregnate. So that's the ideal fly bachelor right there. And basically if you release these sterile males in mass, they will breed the females. The females will say, "Oh, well, I'm I'm pregnated." And they will not go on to produce any eggs. And within a few generations of this, you can actually wipe out all the screwworm in one area.

[00:09:05]This is tested out first on some islands. I think there was an island off of Florida that they tested and also the island of Curacao which was like a Dutch dependency colony. I don't know what you call it at the time. And basically they put a bunch of the screwworm sterile males into there and you know, managed to wipe out the populations. And they used this technique to actually wipe it out from the United States. So by 1959 they had eliminated it from South Florida and from 1966 they eliminated from Southern Texas though there was some outbreaks later, which we'll get into. Um and over the course of the next like, you know, 30 or so years, they basically eliminated it from the entirety of North America and Central America. So, gradually over time for Mexico, they were able to use the sterile uh insect technique uh to basically push the boundaries of it further and further back.

[00:09:56]Um so, by the point of like 2001, they basically had eliminated it from the entirety of North America and Central America. Um the of course uh New World screwworm still existed in South America and the Caribbean, so it wasn't completely extinct, uh and there was a potential for incursions. And several incursions have occurred in the United States since that period of time, right?

[00:10:17]Um there was an outbreak in I think it was I've just got to write down the name here.

[00:10:22]Um this was in Starr, Texas in 1976.

[00:10:26]There was an outbreak there. Um the other major outbreak that happened in that uh until recently was in the Florida Keys back in 2016 and 2017. This outbreak primarily affected the um basically the uh the deer that lived in the area, and this is where you might have heard about the zombie deer. They were like deers that had these like wounds on their heads, usually the bucks from like, you know, bucking each other cuz they're that's what they do. They want to screw as well. And um when they get the wounds in their heads, basically, you know, that gives a perfect place for the screwworm to start doing its thing that way. So, that's where you start getting that kind of outbreak. And they use the sterile insect technique not just with aerial kind of dropping of uh sterile flies, but also with ground release chambers.

[00:11:07]And they were able to get it under control with a very small investment of only a few million dollars to get it under control, which would have saved billions in terms of economic damages there. So, quite a good uh investment there that way. Uh there has been occasional incursions, usually animals or people that were imported from uh South America or Central America, uh where people would have people and animals, um non-human animals, I guess, would have these kind of screwworm infections. and they would basically a doctor would find a little maggot writhing in there and be like, "Ah, what is that?" And they would send it off for testing. It's like, "Yeah, that's a screwworm. That's reportable. Good thing for sending it in that way." So, that's basically how it went.

[00:11:44]And you're wondering, well, if it was in South America, how did they keep it from getting back into the into North and Central America Central America North America that way? Well, there is a place called the Darién Gap, which sounds like a great like male pro tag name in like a romance novel, but it's not that. The Darién Gap is a place in Panama. It's basically a huge section of like like really thick dense jungle and swamp that basically kind of is the border between, you know, Central and South America there. And essentially they were just dumping about 15 million of these sterile male flies there every single year. No, every single week, actually. There's a lot of screwing going on. And these sterile males were basically just being dumped in the Darién Gap for about, 25 years without too much issue.

[00:12:34]Um, what happened was that this line of defense, you know, it worked pretty well, but it wasn't everything. And for some reason, it seems that the sterile flies started to break through the Darién Gap right around 2023, 2024, somewhere in there.

[00:12:51]Once they broke through, then they started to spread more and more northwards from Central America into Mexico.

[00:12:57]By the time we get to November of 2024, um, Southern Mexico has a whole bunch of screwworm cases and it's unable to control it anymore. And this causes the United States to stop all imports of cattle from Mexico, ending a huge amount of trade, millions of dollars worth of losses. Uh, they had already done a few kind of trade restrictions by that point, but by this point it had become a sustaining nationwide kind of blockade that way.

[00:13:22]Um, and it seemed to stick around in Mexico in 2025.

[00:13:28]But, there was worries that the screwworm was heading northwards and that America would soon be hit. To their credit, the USDA did see this possibility at the time and they said, "We're going to start making our own sterile insect facility with the goal of having 3 million or sorry, 30 million sterile male insects per week to be dumped in the area just to prevent any kind of incursion that way." Well, while they did make that investment, unfortunately, it was kind of too little, too late. Um by the time you get to 2026, there was a rapid movement of the screwworm north back into North America.

[00:14:04]And in June 3rd, 2026, there was a calf that was found in Knapp, Texas that had a screwworm infestation. Oh, no, we're getting screwed again. So, uh when that happened, uh it basically caused a international panic, basically. So, very rapidly in um June 5th, uh the USDA basically announces that they're going to halt imports of uh cattle from South Texas to other states.

[00:14:35]Um and Canada also says, "We're cutting off trade of Texas uh Texas cattle to Canada, basically." Which interrupted a huge amount of trade that way, too.

[00:14:44]>> Hey, this is Joy from the editor's desk.

[00:14:46]I wanted to point out that on June 6th, a veterinarian in Southern Texas did find a shih tzu that had 40 different screwworms living in its head. Um this wound was caused by a migrating grass foxtail. That's the sharp part of grass and it can cause wounds, that kind of thing. But, really any small wound can be a portal of entry for these uh screwworms. So, it's very important that if you have your pets and they're outside, um keep them on prevention. The FDA has a list of approved preventatives for screwworms. So, um get them on prevention if you're not already. Um it's really important. I mean, not only for the screwworms, but also for the ticks, the heartworm, and all the other stuff that's out there that's quite nasty. So, uh keep vigilant if you are in the area or if you're in the surrounding states, you may start seeing screwworm there, too. So, it's very important to be safe about this.

[00:15:31]Um as of now, I think there's about 11 outbreak areas in Southern Texas. There was an outbreak in New Mexico, which seems to be inactive at this point, but there's multiple areas where there's been an outbreaks of this screwworm.

[00:15:45]Now, now that screwworm is back, it raises a few questions of how exactly it broke through the Darien Gap and why was it kind of contained so successfully for decades and came roaring back that way?

[00:15:58]Well, there is one theory that I think is somewhat interesting. Um it seems to be somewhat supported by kind of the circumstances there. Like I mentioned, this kind of started before the current presidential administration.

[00:16:11]It seemed that in 2023-2024, that's when they uh started moving northwards. So, clearly there was something going on at that point. But, 2025 is really where this kind of accelerated. And one theory is that the uh Department of Government Efficiency, which was the uh I guess you call it government department, uh that was established by Donald J. Trump, uh then uh current president, um under the uh you [clears throat] know, Elon Musk, right? And Elon Musk's Department of Government Efficiency, he had a chainsaw and he was going to cut back government spending. And there seems to have been a line item uh that was uh they they estimated to be $250 million worth of money going to the Food and Agriculture Organization of the United Nations. Um it turns out it was probably closer to about like $170 million. Still, um they cut off a bunch of funding to the Food and Agriculture Administration. An anonymous source has said that that funding went to be for the uh kind of prevention you know, surveillance and eradication of screwworm in Central America. So, it seems that some of these dog cuts may have been responsible for the break you know, the increasing spread of screwworm or at least didn't help that way. Now, I have to point out that Snopes kind of did investigate this claim and they found of course it does seem that it only comes from a single anonymous source. This idea that it was the screwworm that was contained within that. It is a popular theory and I think there is probably truth behind it, but I don't want to present it as absolute fact at this point because I don't want to get screwed later.

[00:17:48]>> All right, this is Joey from the editor's desk one more time. I just wanted to present my theory as to why I think the screwworm was past the Darien Gap and started getting into Southern you know, Mexico and Central America and into the United States. The big factor for me is trade. The world is far more globalized now than it ever has been and it really only takes a few animals maybe even just one that has an infection with screwworm to pass through the Darien Gap to get in from the Caribbean or from South America and have an infestation of screwworm developing there. And once those larvae drop off and pupate they get into the soil, they could form a stable breeding population in as long as the climate is good that way. And we know that these screwworm flies can fly you know, up to 20 km in normal conditions and up to 300 km if the winds are right and they can transmit that way. So, with the world's increasing consumption of beef and a lot of interstate trade or you know, intercountry trade rather of these of beef cattle in particular, you can get a lot more of this and we also see that dogs are being trafficked from Central South America to North America often in terms of quote unquote rescues or a lot of puppy mills that kind of situation. So, you see a lot of animals moving across borders and this increasing movement of animals across borders can introduce foreign animal disease. So, that shouldn't be too too surprising. Um I think that's a far more important role than just pointing out austerity politics. I mean, there's been a lot of negatives with the austerity politics of the Trump um uh presidency. Um obviously, huge cuts to science, huge cuts to public health.

[00:19:27]Um a lot of people are out of work. It's causing a lot of mayhem. Um I mean, there's the whole outbreak of uh um of uh parasites, fecal parasites. I'll post a picture of this here. Um so, it's important to keep an eye out for that kind of thing. But, in the case of screwworm, it very much is about trade and it's about our consumption of beef.

[00:19:46]It's about our the way that we move animals and the way that our animal economies have become globalized, in my opinion, is far more important important here.

[00:19:54]Um so, that said, we know that the current administration has not been very good with dealing with uh you know, zoo- epizootic outbreaks or any kind of zoonotic outbreaks, that kind of thing.

[00:20:07]Especially with things like avian influenza, there's been a very lackluster response, in my opinion. I made a video about that, too. Um with regards to avian influenza and the response of the current administration that way from the USDA. Um but, also, you know, from the top down, it has not been going well that way. And the anti-vaccine policies of uh certain members like Ronald uh like uh RFK Jr.

[00:20:31]Um so, that is one of those things that I'm not super excited about what's going to happen next in the United States.

[00:20:38]But, I will point out that there have been several encouraging moves from the USDA and the FDA. So, one thing the FDA did, for instance, was approve a bunch of drugs uh specifically uh preventatives that already existed on the market for um the treatment and prevention of screwworm. Uh so, this would apply to horses, uh cattle, dogs, that kind of thing.

[00:21:01]And uh that seems to have made a big a big difference that way. So, uh you know, I feel like that can be a very good starting point. Um, but it should be mentioned that of course this is a very privatized option because not everyone can necessarily afford prevention for their animals. Um, and if an animal does become infected, it's going to be very costly. Um, to remove these screw worms, you have to do it basically manually. Um, this often requires sedation, anesthesia, surgical experience. Um, it also requires a lot of medications to kind of help with secondary infections. Um, there's a lot of concerns and a lot of costs that are going to be associated with this that are going to come down to producers and consumers, unfortunately. Um, and this seems to be kind of the nature of the beast, unfortunately, when it comes to that. Um, while there was a lot of public funding in the eradication of screw worm, it turns out a lot of the control, um, when it reaches the United States is going to be privately funded, uh, out of people's pocketbooks, basically. And the people who are going to be paying for this are going the consumers are going to experience higher beef prices that way. Um, so for instance, I mean, the costs are not simply monetary, right? We also have to consider things like anthelmintic resistance. Now, um, we often don't think of dewormers as being like a kind of a thing that where that, you know, species will evolve resistance against them. But this is often something that happens, you know, we see this with heartworm in dogs. This, uh, you know, especially in the, uh, the Mississippi Basin, Mississippi Delta region, the heartworm parasite has actually evolved resistance to many of the drugs that we use currently. The same sorts of drugs that we use to treat and prevent hookworm. Um, hookworm and screw worm. We're talking about screw worm today. Um, there's also, um, you know, the barber pole worm, Haemonchus contortus, uh, which is one that affects sheep. Um, they actually have also evolved resistance to the same kind of class of medications that way.

[00:22:54]Um, screw worm is also problematic because since it does lead to such big gross disgusting wounds, you also want to use antibiotics. And so, using antibiotics in a large population of animals can lead to antimicrobial resistance as well. So, that's another societal cost we'll have to pay for this outbreak, too. And finally, I mean, it's going to be something where it's going to interrupt a lot of trade. Um and it's going to disrupt, you know, it's already disrupting interstate trade. Uh 15 states so far have said that they won't import cattle from Texas without a USDA certification that the animal's free of parasites. Um that has to be made relatively shortly before importation.

[00:23:32]But, also the international trade with Canada.

[00:23:35]Um and I think that this is going to become more and more of an issue, especially if uh screwworm starts to migrate even more northwards or goes back to Florida or affects more of the southern United States that way. And this could cause billions of dollars worth of damage that way.

[00:23:49]Um I kind of wanted to end this off here with a little talk about uh you know, how this all looks. I posted this uh um basically this quote from on uh Blue Zones Guy, and I'll read it here.

[00:24:01]>> In 2003, Texas cattlemen were asked what was the most significant event in ranching during their lifetime. The foremost response was the eradication of the screwworm. Tobin Armstrong summed it up by stating, "If we had to go back and do the kinds of things we did back then as a routine to cope with the screwworms, nobody's equipped or prepared physically or emotionally to deal with it. It would be disastrous.

[00:24:24]The screwworm eradication program probably contributed more than any piece of modern machinery to the reduction of the population of working cowboys by decreasing the amount of labor required on ranches.

[00:24:36]>> So, it seems like, you know, the screwworm eradication was enormously successful. And the small amount of investment that the government made in maintaining it actually did help avert billions of dollars worth of government losses, pain, and suffering in humans and animals. And that little bit of protection seems to have made a big difference. And you know, if you're going to be screwing around, you also want to be using your protection that way. So, it's very important.

[00:25:02]I just think that having that kind of government sort of intervention in government invest- investment into this kind of thing is going to be very important in the future. And the more and more we live under austerity, the more and more this kind of cost gets deferred to the private sector, to consumers, and to producers that way.

[00:25:20]And so, we have to think about what kind of if we do live under a democracy of some kind where people have the ability to choose who is in office and who's not in office, they should be thinking about which governments are going to be investing in the public good and public welfare of humans, animals, public health, and those that won't. Um so, if it is true that, you know, those did cut a lot of these sort of programs for preventing the screwworm returning to uh Texas, then that should be, you know, on everybody's radar that way. And I hope that this video kind of reaches people and kind of helps educate them about this pretty nasty parasite.

[00:25:57]And uh I really hope that they do manage to use the sterile fly technique to um kind of prevent the uh the flies from coming back. There seems to be some interesting technologies that they are working on in terms of using genetically engineered uh sterile male flies. I will point out that, you know, there are kind of ethical concerns about releasing a large amounts of uh basically mutant flies into the environment that have gene editing technology on them.

[00:26:24]In terms of that, I mean, you would kind of have to weigh the pros and cons here.

[00:26:28]Uh the obvious benefit is that, you know, it will eliminate basically it could help eliminate the thing faster and maybe cheaper to produce these sterile male flies versus using the radiation thing may be a lot more expensive that way, breeding large amounts of flies that way, too. So, you know, you know, there there is concerns about that, but that may be a potential path forward here in terms of dealing with this outbreak. Um so, I hope you learned a little bit about the screwworm and I hope that you realize that the screwing is not just coming from them, it's coming from up top, too.

[00:26:59]So, hopefully you don't get screwed and hopefully we all kind of learn something here today.

[00:27:03]Definitely check out the sources in the description. I had a lot that I tried to gather for this video and I couldn't find anything that was comprehensive.

[00:27:09]So, I hope that this is a starting point for other people to learn more about it and then I might make an update for this video, too. If you wanted to learn more about that in the future or if you wanted to update about how things are going that way in the future. So, don't get screwed. Use your protection.

[00:27:23]If you can afford prophylactics to prevent against screwworm for your animals, dogs, cattle, horses, that kind of thing.

[00:27:29]You know, an ounce of prevention is worth a pound of cure. So, don't get screwed.

[00:27:34]That's all I had to say today. Let me know if you like the video in the comments. Peace.

[00:27:39]So, I I really don't know that much about woodworking. So, if I'm a screw up, let me know.