One screw worm infestation that goes unreported could erase the tremendous gains that have been made in the Southwest against this insidious, multimillion dollar pest.

The screw worm eradication workers can protect the gains, but only if they know where the pest strikes.

You can help.

Stopping screw worms is your concern, especially if you own livestock or a dog or cat or any other pet.

All of you can help by finding and reporting screw worm infestations.

Examine your animals at every opportunity.

Look for cuts, scratches, or other wounds.

If you find a wound that contains insect eggs or lobby, take about a dozen worms and all eggs from the wound.

After you've taken the samples, treat the womb with approved insecticides.

Place the samples in a container or jar in alcohol or water.

At this point, speed is important.

Call your county agent.

He'll tell you where to send the samples.

He'll tell you what action to take.

Positive identification will be made by experts and measures taken to eliminate the parasite.

A screworm infestation confirmed by positive identification sets off a series of emergency activities at schuwirm Eradication Headquarters, Admission, Texas.

Here, millions of screworm flies are being read each day and made sexually sterile by exposure to gamma rays from radioactive cobalt.

Released in special patterns and in large numbers, these laboratory reared flies fight for us against an outbreak.

These sterol screworm flies mate with native flies, which in turn cannot reproduce.

Release of steril flies, combined with intensive livestock inspection and use of insecticidal treatments, has already stemmed outbreaks.

This new technique for insect control is eliminating screw worms from the Southwest.

Complete success depends on quick discovery, quick reporting, quick action.

Remember, examine, collect, treat, call you a county agent, and help stop schoolworms.

That's the whole episode, is it not.

Isn't that amazing?

It's so comprehensive.

It's so comprehensive.

I okay, So that was from I found that on the USDA National Agricultural Library and like the screw worm exhibit, and it was a video produced in nineteen sixty three and it's called Lookout for screw Worms, and I just it was I think I didn't realize the extent to which screwworm was such a big deal during that time period for decades and decades and decades, enough so that there are like promotional videos like this, right, Okay.

I'm really excited, Aaron to hear you talk about the history because I was reading and didn't realize like a lot of the history of like ranching the US was driven by screwworm.

Yeah, I know, I know, And it's so funny.

Yeah, I mean, there's there's so much to cover.

We'll get into it.

Okay, I want to start right now, but I want you to we'll start instead with introductions.

Hi, I'm Aaron Welsh.

And I'm Erin Almann.

Update.

This is this podcast will kill You.

And today we're talking about screw worms.

Shrew worms specifically for me, I'm talking about New World screwworm.

Yeah.

Well, we'll go over both different types of screwworms, new World and Old World, but realistically we're mostly talking about New World screwworm.

Today, the one that's been in the headlines, in the news, spend in the news big time.

It's gonna be a really interesting episode and a little bit maybe creepy Crawley as told to me A little bit, a very very creepy crawling.

Yeah.

Some of the descriptions I have are hard to stomach.

Okay, that's good.

I don't have that many of those.

Okay, okay, I'm keeping it basic.

But before we get into all of that, it is quarantine quarantiny time.

Yeah, what are we drinking this week?

We're drinking there's creworm driver.

Yeah, it was just a screwdriver.

Screwdriver which is, you know, vodka and orange juice, and with the addition of a gummy worm.

Gummy worm to represent screw worm.

We're getting real creative with these erin you know.

I think that's okay, It's totally fine.

Okay, it has to be.

It has to be.

We can do nothing else.

Yeah, yeah, yeah.

We'll post on the places that you can find it, like our website.

This podcast will kill you dot com someday, but also definitely on our socials.

This podcast will kill you what socials?

Oh I have I try to post one.

I don't know if it works very well.

I can't figure out the dimensions, but hey, we're working on it.

There's no way to do.

Listen, there's a way.

There's a lot of other great stuff on our website.

Yes, there is.

If we've got transcripts, We've got references for all of our episodes, so if you want to read more about screwworm, that's a great place to go.

We've got links to merch to our bookshop dot org affiliate account, to our Goodreads list, to music by Bloodmobile, contact us, form a, submit your first hand account, form Patreon, other things.

Probably check it out.

There's a lot there.

Yes, podcastwikill you dot com.

If you haven't yet radio reviewed and subscribe, please do that.

We'd really love it.

We're on YouTube on the exactly Right network channel, and we're on all of your favorite podcasters including iHeartRadio, Apple Podcasts, Spotify, the like, the moving on, moving on?

Are we done?

Should we be great?

You ready?

Yeah?

I am.

I'm going to tell you about the biology of screwworm really fast, so that you can tell me about the history.

Okay, okay, let's take a quick break and then we'll get to it.

The star of today's show is the screw worm, which is a larval form of a fly.

Most people, when we say screwworm mean the New World screwworm, which is the species Cochlio maya Homnivorax.

Might have pronounced that wrong, hominivoras.

Listen, it's the New World screwworm.

But there is another one, the Old World screwworm, which is a species called Chrysoma besiana.

Okay, and these are two different genera of fly, but both of them are blowflies overall not entirely dissimilar to the flies whose larval forms not that long ago an episode we hailed for the benefits of their ability to help heal wounds.

Yeah, this may change our feelings on maggots.

I think it will, because today we're talking about pretty much the exact opposite.

Unlike most other species of blowfly, the New World and the Old World, screw worms larval forms feed not on necrotic or dead tissue, but instead on the warm and living tissue of warm blooded animals.

Yeah.

So, screwworms are a type of fly who lay their eggs in the flesh of living mammals in a way that causes really significant harm.

Kind of like botflies, but more harmful, way more harmful.

That So, what I want to do in this part of the episode is really just kind of take us through, like what are these flies?

What do their life cycles look like?

And why do they cause as much damage as they cause?

So that you can tell us about all of the history with them, because I know it's really interesting.

So adult flies of these both of these species, they look fairly similar.

Most of what I'm going to talk about is about Cochliomaya, Hominivorax or the New World screw worm, but it mostly all applies to the Old World screwworm as well.

They look a tiny bit different, but otherwise they're really quite similar.

I'm so interested in their evolutionary history, which I didn't look up, like the relationship between them, was it like independent?

Yeah?

Anyway, Like oh, I didn't look at it either, but that's really interesting, Like yeah, how they both end up evolving this way of life that's so different from all of their other brethren, right.

I mean it's a it's a great you know open niche I guess, like, yeah, someone else has got all the dead ones.

You can get the live ones right exactly anyway.

And so the adult flies, all entomologists everywhere are going to kill me for saying this.

They look like a fly, Okay, how big, a little bit larger than a horse housefly.

Okay, not a horsefly, housefly.

And that's literally what they look like because they are blowflies.

A lot of the houseflies that we see not houseflies, aren't necessarily blowflies.

But you see these around.

They've got almost like a metallic ish kind of bluish greenish body like most blowflies do.

They have these big, giant orangish eyes across their heads, and then they have these three black and gray stripes along their back.

The Old World screw worm has two of those stripes.

Okay.

The New World screw worms are native to essentially the entirety of the Americas, though they are primarily a tropical species.

They need warm, moist soils in order to complete their life cycle, which goes something like this.

The adult flies emerge from the soil where they pew paint, and it is only the adult females, As is usual for flies who cause the majority of the problems, they mate just one time.

This is important, usually around day three to five of life, and then they start laying eggs right around that time day five to seven, after they come out of their people form, these flies lay two hundred to three hundred eggs.

Some estimates say as much as five hundred eggs per clutch.

It keeps getting worse, yep, because they lay additional clutches every three to seven days, for up to eleven clutches of two to three hundred eggs in a lifetime.

And we can air in mathis though we don't have to because it's all over the papers.

They lay a maximum of three thousand eggs per single female screwworm fly throughout the course of their twenty plus day adult life.

I mean that is some hard work, it really is.

They also often leave each one of their clutches in like several different egg masses, so not all like two hundred and one spot.

They'll lay them like over of course of a few minutes or a couple of hours, in multiple times.

Right, don't put all your eggs in one lesion.

Kind of a mentality, exactly exactly, And they do.

They lay their eggs in lesions on the margins of wounds on warm blooded animals, mammals, possibly birds, though they don't tend to prefer birds, but they can but all mammals, and they tend to prefer the kind of drier margins of fresh or bloody wounds compared to wounds that are severely infected or really wet or have a lot of like bacterial purulence.

They want the freshest of flesh.

The freshest of flesh, and they especially prefer wounds that have already been infested with screwworms, kind of like a signal that gets sent out like, hey, this is a really great wound, go ahead and lay your eggs here.

However, they can also lay their eggs on other easily accessible parts of our like thin skin or mucous membranes, so say, the corners of eyes, or in noses yep, or near the perineum, or especially in places like insaane newborn mammals like newborn cattle or goats or horses that have an umbilical you know, stump that's not fully healed.

That's a really common spot.

Yeah.

And then after a day or so, these eggs hatch into hundreds of maggots, the larval form of a fly, and these maggots eat their way in around and under the skin of their host, literally bear trying themselves in the process, which is how they get their name screwworm.

Their wriggly little maggot bodies are even grosser looking than most maggots they have.

It's not a thing.

I mean that is a high bar.

Maggots are disgusting looking.

Maggots are gross looking.

But these ones have particularly sharp hooks eyes of their mouthpieces, and their bodies have these sets of rings that kind of point backwards of these spines, these rings of like you know, like the kind of spines where like you can drive over them, but don't drive backwards.

Yep.

Yeah, and that is what helps them literally cork screw their way deep into the living tissues on which they're feeding.

How big do these larvae get?

Oh, that's a really good question.

I actually didn't see anything about the particular sizes.

I mean, they're not large.

They're small individually, maybe a few millimeters big.

Okay, okay, can Yeah.

They feed for about a week before dropping off to pupate in the soil for another week, and then they'll emerge as adult flies.

And once they emerge, okay, so I'm thinking about like going to in a place where screwworm is present.

How many you said that the females only mate once, and so how many rounds of females in a year is happening, you know what I mean, Like, right, it's not like idea, it's like one week then do they overwinter, et cetera, that kind of thing.

Yeah.

So, I mean they tend to live in the tropics, and in the tropics, they're there all year round, right, and so they're going to be continually in each female.

Adult females live for about twenty ish days, ok And then you know they're going to lay their eggs starting on day like four or five, and the eggs only take about a day before they hatch, and then they feed as larvae for about a week and then they pew paint for about a week.

And so their whole life cycle is maybe what's that like a month a little more than a month, Okay, And so you could be getting twelve plus rounds, I mean, plus each female is laying like three thousands.

Yeah, I can't even calculate.

That's a lot.

It's just hard to comprehend.

Like like they I feel like they would run out of living tissue to eat.

It's an interesting So it's actually really interesting that you say that because one of the one of the papers that I read was looking at like the overposition behavior of these flies, and they were pointing out that, like if you look at the way that they overpause it, and like how frequently they do it, and how they lay their eggs in these like multiple different clutches and all of this, but they do it multiple times in their life, right, Like a lot of a lot of flies or other insects might just lay like one giant clutch and then go ahead and die.

But the way that these particular screwf lines do it, they at least in this paper, were saying that this fits with this strategy of like exploitation where they might be evolutionarily finding niches that aren't always there, right in an environment that's not always favorable.

And so you've got to be able to take advantage lay a whole bunch of eggs as soon as you can and as quickly as possible when you find the right wound, because you don't know when you will again, which suggests that in nature, the perfect wound over position site might have been harder to come by.

But then enter live stock livestock.

Yeah, and now there's basically free terrain.

Because when I before I started researching this, and when I thought of like the wounds that screw worms were causing, but also that they were first laying their eggs in.

I always thought of like a huge, gaping like wound, right, like some kind of large hole, some infected something.

But actually that's not the right image to have.

The types of wounds that these flies can overpose it in to begin with, can be as small as a tick bite.

And often are from a tick bite exactly.

And so it's any break in the skin, a scratch from a thorn or a fence wire, like I said, the belly buttons of newborn animals insect bites.

The wounds that can then be caused are incredibly substantial, and animals, especially livestock animals, can die within a number of days to weeks after infestation with a screwworm or it's multiple screwworms, because of how deeply these screwworms can wander and destroy tissue along their way, and because of things like secondary bacterial infections that can occur from you know, just the open wound that is caused by these maggots.

So that's that's like mostly screwworms arin.

And Okay, so between the Old World and New World, are there differences in the severity or in the number of eggs, or you know, whatever it is.

It's a good question.

It was like weirdly hard to find great papers on the Old World screwworms.

So from what I can tell, they they don't tend to be maybe quite as severe or at least not as deadly as quickly.

Okay, Okay, I don't I don't know exactly why, Like what are you know, all of the specific differences between them, As I know you'll probably talk about, the biggest difference in how we've dealt with them is that there are not as many programs that are widespread to try and eliminate the old world screwworms.

So it is very much still a problem throughout its distribution.

I see, whereas we have changed the current distribution of the New world screwworm.

Yeah against us you will.

Yeah.

And then in terms of like how do we manage it?

Aside from what you're about to talk about, I just keep like putting little putting, little teasers out there.

We don't have any kind of vaccine, we don't have any kind of like specific treatment for screwworms.

It's basically when we're talking about livestock insecticides on the wounds or like insecticide dips and things to try and help prevent the screw worms infection to begin with, we can also use avermectins like ivermectin, so for humans with when there is human infection, because there can be, and there there is.

This is also a public health problem, not just a livestock problem.

Yep.

It requires oral ivermectin.

And this doesn't like get rid get rid of the infection per se.

What it does is paralyze the larvae, which then have to still be removed thereafter.

Okay, it paralyzes the larvaie how interesting?

Yeah?

Yeah, So our main stay of dealing with the New World screwworm has been sterile insect technique.

It's so cool prevention.

Tell me all about it?

Is it?

Really?

Yeah?

I don't have any more great.

Is going to be basic and straightforward.

I'm excited.

All right, let's let's get started.

So to help me set the stage for the history of screwworm, I've brought along some assistance.

Aaron.

I can't wait.

Please open the video titled screw Worm one.

Three hundred million years before man appeared on Earth, the insect was here with time to develop varieties so diverse.

Their numbers are beyond conception, roughly a million species along with ticks and mites, three fourths of all the animal kingdom.

Of these ten thousand species are man's mortal fol endlessly vying with him for food and fiber, endlessly looting what he has sown and ended.

Did you like that?

I loved it, Aaron.

I really hated the grub Those were grubs, not maggots.

Listen, the video is like everything grubs country.

Yeah, that was clear.

It's so fun so that I loved it so much.

That video is from It was produced by the US Department of Agriculture, the usd DA in nineteen sixty nine, and it goes into some of the various like insect and plant pests screwworm that I've been plaguing farmers across the globe.

I also thought it was interesting because it was like one million species, and I looked it up and I think we're now at like five point five million species.

One million is such an underestimate, right, It's like doctor Evil, like one million dollars.

Like that's kind of what it reminded me.

See.

Yeah, but Yeah, I went all in on video clips for this episode you're about to find out.

So, Yeah, there's an amazing archive work at the National Agricultural Library on the USDA website and as well as the Internet archive, which is just one of my favorite things in existence.

But but I wanted to start the history of screw worm with that clip because I feel like it transports us back to a time when New World screw worm was among the top threats to agriculture here in the US.

And by the way, I'm going to just be focusing pretty much only on New World screw worm for this which I'm just calling screwworm for short.

That's what most of the literature does.

It's fite.

It was hard for me to find stuff on old world screw worm.

Yeah, but it's eradication from North and Central America in nineteen ninety one, which spoilers it was eradicated and spoilers it's back.

It marked a tremendous achievement in pest control and a demonstration of what was possible without the use of toxic pesticides.

It was a big deal.

Hence the sheer volume of material that's out there about the screw worm eradication program, and after it was eradicated, it dropped out of the news cycle for the most part, except, of course, in the places where it was still prevalent, like most of South America, and the recent headlines about the reemergence of screwworm here in the US that might be the first time that many people have learned about or heard of this parasite, but in fact, it has plagued wildlife, humans, livestock in the Western Hemisphere for thousands of years, and so using genetic analyses, researchers recreated the historical spread of this parasite and found that it seemed to follow human migration throughout the Americas, suggesting yeah, as human migration continued across North America and then down into Central and South America, the screw worm followed them.

And then the introduction of European livestock starting in the fifteen hundreds, of course, provided even more hosts and wherever it went, as long as it found a host on which to feed, and it wasn't too picky, It'll pretty much feed on anything that has living flesh and with suitable yeah yeah yeah, warm flush, warm flush, yeah, and with suitable climate conditions, it would just do its horrific thing wherever it could.

And so last season we talked about how we did this episode on medicinal maggots and raved about how cool they are, which is so true.

But the maiasis from screw worms is another matter entirely.

It's not the same.

It is not the same.

I found a quote from ce Scruggs from nineteen seventy five that I think pretty much sums it up for me.

Quote, it is doubtful that the mind of man could create a more vile scene than that of worms consuming the live flesh of one's body.

The imagination almost refuses, particularly in this day and age, to conjure up the horrendous pain and outright revulsion that must come to a person infested with a writhing, seething mass of worms steadily tearing and consuming his flesh.

End quote.

It's I mean, it's truly awful.

It is truly awful.

Yeah.

Yeah, And this feeling, this image, the sentiment towards myasis.

This might have been what the guy who first described the New World screw worm was thinking when he gave it the name.

The species name of haminivorax, which is man eater what it translates to.

And so the guy who did this was named Charles Cockrell.

He was a surgeon in the French Navy stationed at a penal colony Cayenne in French Guiana in the mid nineteenth century.

Conditions at this penal colony were so awful apparently that it was given the name Devil's Island.

And while he was there, he treated five men who were suffering from screw worm infestation.

Flies had laid eggs in each of their nostrils and masses of larvae developed in their nasal sinuses, consuming the surrounding tissue.

I know three of the five men died as a result of these infestations, and apparently three hundred larvae were recovered after rinsing the sinuses out with water.

Yeah.

Yeah, these ol passages seemed to be a really commonplace and there's human infestation.

That it makes sense.

You just can't get at it easily.

Yeah.

Well, and a lot of times too, there's there's there's something else going on, like you like you're in a place where you don't have access to be able to move around or clean your surroundings or whatever, or that you're sick with something else, so you're not able to like swat flies away.

That's that sort of a thing.

But it's still it's it's truly, it is truly awful.

And I think that Cokeral himself was quite a bit taken back by what he saw, and he wrote in this description of treating these men that science is quote powerless to prevent these terrible ravages, and in that he would ultimately be proven wrong, but it would take another hundred years or so for science to have a fighting chance, and in the meantime, screwworm continued its path of destruction.

In the second half of the eighteen hundred's cattle ranching banded greatly across the southwest US, especially Texas, and millions of acres were transformed by grazing, and also four grazing windmills were built to bring water to the surface for water holes.

Screwworm flies like water, so that was one, you know, helping helping it along.

Overgrazing meant fewer prairie fires, so more continuously occupied habitat, more continuous host for the screw worm, and deer replaced antelope as the dominant game animal, which grew even more abundant, so like deer herds, of course, are like can be enormous, so that's like even more hosts for the flies.

According to one researcher's observation from nineteen fifty nine, deer are often victim to repeat infestations, leading to two to three thousand larvae in one wound.

Oh goodness, and that amount of maggots of two to three thousand can destroy an area apparently seven inches wide and seven inches deep or eighteen centimeters wide and deep.

Seven inches on a deer's body.

Can you go seven inches deep without hitting some vital structure?

Yeah, I guess you.

That's you can't.

Yeah, yeah, I mean wound wounds like these are can be deadly or often deadly, and in bad years, up to eighty percent of fawnds of white tailed deer were killed from these infestations.

Oh yeah, and these deer also provided ample hosts for ticks, specifically the Gulf Coast tick or Amblio mammaculatum, which prefers to feed on the ears of livestock, and as we know, screworoms can lay their eggs in any wound, including tick bites and cow's ears are often a casualty.

You can tell is this a screwroom infested area because all of their ears are just like gone or shriveled or yeah, partially torn.

And apparently up to ninety percent of some of screworom lesions start from a tick bite in some areas where the tick is especially prevalent, and then others through common farming practices like castration, branding, dehorning, and then like you mentioned, newborn livestock are often affected at the navel.

And on top of that, so we've got all these things going on right, Like, we've got more cattle, we've got water, we've got deer, we've got fewer prairie friers.

This is all happening.

And then you've also got the demand for beef skyrocketing since the development of refrigeration allows you to ship the meat that you don't sell locally, which previously had restricted herd size.

And so now you've got the opportunity to create these massive herds because you can ship ship.

It the meat.

Oh wow, Aaron.

Put it all together, and what you have are the perfect conditions for a screw worm storm.

Just take over, just absolute takeover.

And this parasite truly plagued the areas where they were established, and it was a horror for livestock owners.

Quote this is a quote from one of these owners.

Particularly disgusting and sickening job was when cows or calves got screw worms in their mouth and gums.

This came about in two ways.

One, the cow or calf, if they could reach the wound, would try to lick the worms out of the lesion.

Thus some live worms would get in the mouth of the animal and take hold.

In some cases, I'm sure that flies would also lay eggs in the mouths of the newborn calves.

You couldn't use any medicine, just remove the worms and hope you get them all.

Some cases would be so bad that an animal might lose some of their teeth.

It sure wasn't a job for anyone with a queasy stomach end quote.

Oh, I've seen some pictures of that in like sheep's mouths, and it's so awful, awful, and.

So you're trying.

I mean, imagine you have a herd of cattle and you have to spend so much of your time trying to do this.

Like it was a losing battle too, because, as you mentioned, infected lesions will attract more flies, so they use a quote straw color and often bloody discharge that attracts more flies, resulting in multiple infestations by hundreds to thousands of maggots of all sizes.

Death is inevitable unless the animal is found and treated.

The horror of screwworm infestations was deepened by how inevitable they seemed.

You could react, you could treat the animal, but how do you prevent them from attacking in the first place.

Part of the issue was a misunderstanding of the screw worm's biology, which was only corrected in nineteen thirty three.

So for decades the screw worm was misidentified as just a regular type of blowfly, one who primarily fed on carrion and only on live flesh sometimes.

So it was like, okay, opportunistic live flesh feeder, And so it was thought, okay, well, if you get rid of all the carcasses on your range land, that is going to prevent the screw worm from see being a problem.

But since its exclusively on live flesh, it actually doesn't really do anything right, And so recognizing that aspect of its biology was a huge step forward, and that happened in nineteen thirty three, and around the same time there was another development that would revolutionize the way that we dealt with screwworm, and that was a newly minted entomologist joining the cause.

In nineteen thirty four, Edward F.

Nipling, a recent master's graduate from Iowa State University, started work at the USDA, where he was tasked with, among other things, collecting and counting screwworm flies cotton traps.

Nippling was no stranger to screwworm.

He grew up on a farm in rural southern Texas.

He was one of ten kids, and the farm is how they produced most of the food for this his big family, so they would all be, you know, take part in dealing with the livestock, and he described removing, having to remove and look out for screw worms among other agricultural pests.

Before he went to college, he was aware of screwworm and the problems that it could cause, but it was at university that he gained a fuller perspective of how much insects have affected humanity, not just as livestock or agricultural pests, but also as vectors of disease, killing hundreds of millions of people around the world.

He knew that control of these disease vectors and agricultural pests could save lives and livelihoods, and so while working at the USDA, he got to see firsthand how powerful some insecticides were, like DDT, which was just sort of like, you know, really this revolutionary thing, kill it all, and also how quickly they lost their potency as insects grew resistant.

Not to mention the toxic impacts of some of these pesticides, right, and so he realized that a different, more proactive approach was needed.

And play the clip titled screw Worm two.

Okay, this is so fun.

Screw Worm two.

What we really need is some way to control the screw worm before they attack the animals.

And rather than the just wait until after the animals had the tree worm, then try to control it.

I realize that you would never never really control the screw worms that way.

What we needed was some preventing major But how to control the screw worm on hundreds of thousands of square miles of territory, of course seem like tremendous undertaking, and the use of insecticides something like that seemed out of the question, and no doubt was.

But then I conceived the idea that perhaps we could rear of the screw worm and have it some genetic deficiency, that then it would release and release those genetically deficient insects into the population.

They would mate with the normal, normal flies and transmit to detrimental characteristics.

Just how I came to that conclusion, I really have a little difficulty even today, but.

Is amazing.

He's like, I just kind of knew he had to do it.

I don't know why I knew it, but I did.

He's like I did.

Yeah, He's like, I don't know.

I have this brilliant idea and I have no idea how I came up with it.

I love that.

I love that.

So that was Yeah, that was That was doctor Nippling himself, interviewed in January two thousand as part of an oral history project for the Rural Eradication Program.

Yeah.

Wow.

And so what he's talking about here is what you mentioned AARON, which is the sterile insect technique, which is an insect control measure where large numbers of flies are made sterile and then released, ultimately leading to a massive decrease in wild population sizes, and the idea behind this is that the sterile males are really that are released, will mate with the females, they won't produce any eggs, and so there will be fewer and fewer screw worms over successive generations.

And there are a few aspects of the screw worms biology that help this technique to be successful.

The first is that screw worms, like you said aaron, tend to mate just once, and so if they mate with a sterile male, there's no viable offspring.

Yeah, that's what.

And the females mate once, but the males mate like up to ten tonal times.

Yes, yes, so one sterile male could be mating with ten non sterile females and then they're not laying any eggs.

Yep, yep, it's And then the second thing is that in the screw worm affected areas in the US, which is more like subtropical, only a small proportion can survive over the winter, and so if you hit that area hard enough with steril flies one year, you can really make a dramatic impact, and so that.

Can really reduce that population size to begin with.

That actually makes a lot of sense.

Yeah, nippling wasn't the only one to come up with this idea or idea similar to this, like eradication or elimination via sterilization.

There were a few other scientists that also proposed something similar in like the nineteen thirties and forties, but he was really the only one or the first one to get it off the ground, and for a number of years, you know, after coming up with this idea, he was like, Okay, he had the idea first, and then he was like, how do I actually implement this, Like what how do I make them sterile?

Yeah, and he a colleague in nineteen fifty was like, hey, have you have you heard of this paper?

Have you read this paper by HJ.

Mueller?

He used X rays to make Drosophola fruitflies steryl In nineteen twenty eight, that's when the paper was published, and Mueller had actually been awarded the Nobel Prize in Physiology or Medicine in nineteen forty six for what he had shown in that paper that mutations can be induced by X rays.

And this, of course like alerted the public to the dangers of radiation and was like part of the whole like oh god, you know, oh no, when Nippling read this paper, he was like, oh my god, this this is it.

This is what I've been looking for, right, you know, I mean.

Paraphrase my flies.

Yeah, And so he reached out to Miller to be like, hey, do you think that I could use X rays to make screw room sterile?

And Mila was like sure, Like I think that sounds great real yeah, And so Nippling borrowed an Army hospital X ray unit to give it a go, and it worked, like not only were the males sterile, but the females that mate it with them were also effectively made sterile because again they only reproduced once.

And later they switched from X rays to like other methods of radiation, which gave more consistent results.

But you know, once they tested this out in the lab, all they had left to do was actually, you know, see if it worked in real world settings.

And the first trials were carried out beginning in nineteen fifty one on Santabel Island in Florida, and when it was two hundred to three hundred steril flies were released each week.

How did they get so many flies, you might ask?

They had to rear them in the lab.

And because these live on you know, like flesh.

They used ground meat and blood.

Iaine, just like the smell of that rearly.

I feel like I.

Read several papers where people were talking about the smell and like the process of finding the right Actually read a really interesting one about the lures that they use now, like when in their monitoring programs they have a loom.

The lure is called swarm lure.

I think we're on version four, and it's like this concoction that they made based on looking at what are all of the scents and the things that are emitted by the meats and the blood and the overposition fluid and all of this other stuff to try and make a lure to attract them.

And it's like a lot.

It's so gross.

I love that though, I know.

Yeah, I mean that, like I don't.

That seems to me like complete alchemy, Like that's magic to be able to be like, what are these compounds?

Let's make this.

There was so many people that you have I doing stuff like that, but for agricultural pets.

Agriculture, yeah, yeah, it was just it all sounds it all is amazing to me.

I love it.

Yeah.

But anyway, so with the Sannibal Island, you know, real world experiment.

The screwroom fly populations did drop over a couple of years, but they weren't erradical.

I mean, and they dropped dramatically, but they weren't eradicated entirely.

And that's probably because fertile female flies flew over from the mainland.

But like, and what they really needed I think what the US government was looking for outside of the USDA, but like the you know, the people who were providing the funding, were like, we need one hundred percent perfect eradication, must be eradicated, right, yeah, and so this is kind of this yeah, and so they were like, we got to do something else, like what what else?

What else?

But this So there was a kind of a lukewarm reception to these results, and so the US government wasn't really keen on continuing trials.

They were like, we tried it, but I'm not sure.

But then there was an agricultural officer on the Dutch controlled island of Kurrasau who reached out to Nipling for help with their screwworm problem, which was huge in nineteen fifty four.

Nippling was like, let's do this.

So that dropped more sterile flies on to currasau and screw wrooms were eradicated within fourteen weeks, which is four to five generations.

Fourteen weeks, Yeah, eradicated, eradicated.

Wow, I didn't realize it was that fast.

That's bananas fast.

And so this, finally, this was like proof positive that Nipling's idea could work, and so the US government was like, Okay, sure, I guess and the dream of actual widespread screw worm eradication got a whole lot closer to reality, and it demonstrated that you could effectively control agricultural pests without the use of toxic substances like DDT and actually, in the like one of the last chapters of Silent Spring, Rachel Carson wrote about nipling work as like a hopeful path for the future, like we can use biocontrol in a way that doesn't like destroy the environment.

Yeah, wow, it's very interesting.

And so construction on bigger fly rearing facilities began, including one that was capable of producing two hundred million flies a week, which was a feat that required one hundred and twenty tons of meat, one hundred and fourteen thousand liters of water, and thirty eight thousand liters of blood each week.

Would you like to know what kind of meat I really got into the the round?

Okay, it included horse meat, whale meat, and ground up nutria.

Those whale meat listen.

I don't know.

Later on, I don't think that this stretch.

I think that they were like, this is not sustainable.

We need to do something else.

And so they developed like a gelled substrate that was like dried cow blood, egg milk substitute, and some formaldehyde to prevent it from spoil.

So they found something else that was less not yeah, yeah, And so after they constructed these fly wearing facilities, they were like, let's get this going.

And so in the early nineteen sixties and eradication program began that targeted the entire southwestern US.

By this point in time, screworm had been eradicated from Florida by the late nineteen fifties, and so over that decade.

Over the nineteen sixties, screwroom populations plummeted erin if you will play the clip titled screwworm three.

Okay, in this half of our century, man has conquered the atom, the frontiers of space, the depths of the ocean, could not this advanced technology be applied to controlled pests with even greater effectiveness and safety.

Within the last decade, radioactive cobalt sixty has been used to sterilize millions of pupie of the male screwworm fly, whose parasitic larvae breeding in the flesh of cattle, beer, and other animals posed a major problem to our livestock industry in the southern half of the nation.

Once the pupie developed, huge numbers of sterile male flies were dropped over infested areas to mate with female flies, soon drastically reducing the population of a major threat in America.

So that was them doing the irradiation, right, yep, Yeah, that was them dropping Yeah.

So that video is from the same clip that I played at the start of this, from nineteen nineteen sixty nine clip.

And despite the haunting music, like the narration ends quite optimistically, right, like this is the end of scrooms.

We're starting to see like we are conquering right.

This weird by the way that the video I don't know if I mentioned this, but the video is titled who Shall Reap?

Yeah, it's kind of anyway, The whole video is great.

So this is a total side note, But it's so interesting to watch these old videos that are so like slow and the way that they're like the narration is like this, and then like even the clips of everything, and I'm like, if this was today, it would be.

Like screwworm like one thousand cuts, like a million cuts.

Yeah, you never actually see a fly because it would just be like like.

Anyways, education by a million cuts.

It's true, but yeah, so but this, I feel like the optimistic ending from that clip did play out for a while, like that is the way that it was.

It was looking at least in the southwestern US.

But the feeling was unfortunately short lived because outbreaks of screw worm began popping up in nineteen seventy two to nineteen seventy six and then nineteen seventy eight as well, And you know what was going on.

Part of it was suitable conditions for screw worm development, so like it was a period of warmer and wet weather that provided just more habitat.

And then another was reduced care for livestock, so like fewer and less frequent inspections.

Once you think screw worms are gone, one gets through that one starts.

A huge problem you're not checking as much.

Yeah, But these were I think relatively minor factors compared to the real reason for these outbreaks, and that is that parasites don't respect arbitrary political boundaries.

No, they don't.

They don't.

And so the eradication program successful as they were only focused on the US side of the border with Mexico.

And since these flies can travel up to one hundred and eighty miles or two hundred and ninety kilometers, fertile flies could easily travel to treated areas.

That's a huge flight range.

It's wild such a huge flight range.

Yeah, and so the flight range though of these of these flies was not known when they started the eradication program.

I think this was like one of the lessons learned right away.

Yeah.

And so after the first of these bad outbreaks in nineteen seventy two, which there was ninety five thousand cases were recorded, I'm sure that it was actually higher than that, the two governments, the US and Mexico signed the Mexico United States Screwworm Eradication Agreement, and about ten years and a giant fly rearing facility later capable of producing five hundred million sterile flies per week.

Unbelievable.

The numbers are unfathomable.

Truly, truly, but things started to look pretty good.

Things were looking actually pretty great.

By nineteen ninety one, all of the US and Mexico were declared free of screwworm.

And there was a scary blip from like nineteen eighty eight to nineteen ninety two when infected cattle were brought into Libya infested with the New World screw worm, and then that made people super concerned about like, hey, this is gonna take over, Like this is going to spread everywhere Africa, Middle East, Europe, And so a bunch of sterile flies were released, and by June nineteen ninety two, the region was declared screwworm free.

And this really demonstrated the importance of well, first of all, it demonstrated the power of the steril fly, the sterile insect technique, and the importance of thoroughly inspecting livestock for possible sides of infection.

But that can be difficult to do.

But do you know who's really good at it?

Dogs?

Dogs.

Yeah, there are dogs that have been trained for this purpose today.

And I think the first screw worm detection dog was there's a paper.

His name was Casador, which means hunter, and he was trained by researcher John Welch to work at quarantine and inspection stations and he had a success rate of ninety nine point seven percent.

And the only time that he didn't identify is when he had like some gi bug and so he was sick and needed to rest.

Oh, they made him work, even though we sit.

I don't think they realized.

Yeah, but it's like, it's so sweet the paper I have it.

It'll be on our in our show notes or like our in our on our website, and it's he's thanked in the acknowledgments.

Oh, that's so cute it is.

And his leash and his ashes are in the National Agricultural Library in the schworm unit.

Wow.

No, anyway, isn't that.

I just loved that.

We'll put a picture of cat.

We'll try to find a picture of KZ somewhere.

There are lots of them.

But so anyway.

Over the nineteen nineties and into the two thousands, eradication efforts in the Western hemisphere continued into Central America and the Caribbean, and they were largely successful, at least for a time.

But eradication has proved to be a moving target, and screwworm has re emerged in areas where it was previously declared eradicated.

And in light of that, I want to play just one more clip for you, So play screwworm.

For what lesson can we learn from the screw worm program?

Well, to me, it's it's a remarkable program, and I sometimes wonder how it ever materialized in the first place.

In our they were able to get this program underway, But it confirms something that I'm absolutely confident of, and this is that if we're going to deal with major insect pest problems, we're going to have to deal with from an area wide standpoint.

That we cannot deal with these best problems by just trying to control them, uh a year after year on a farm or farm basics.

Just like we never would have controlled the screw in that way, we will never control the bow weaver or or the corn airworm, or the cabbage loafer or carling moth or whatever.

You will never control these insects this way.

I mean, you control them, but you will not reduce eliminate the threat that but there is or possibility and that we can do the same thing for dozens of other insects.

Oh, Aaron, I love that because that's like the conclusion at the end of my section as well.

I know it.

Just like I said, that interview was recorded in January two thousand and the lesson is as relevant today as it was then.

And extends so far beyond just insect and agricultural pests.

Yes, it's doctor, I mean, thank you.

It's public health.

Yeah yeah, like global yeah, global health, all of that.

And so yeah, with that, Aaron, I'll turn it over to you to tell me where what the people really want to hear, which is where we are with screwworm today.

Oh, let me tell you it's not great.

Yeah yeah, every week still to this day, for decades now, planes drop millions of sterilized insects, which are grown and irradiated.

They use slightly different techniques now in a lab in Panama.

They've moved.

The labs are no longer, the rearing facilities are no longer in the US, no longer in Mexico.

They are in Panama, and millions of sterilized insects are dropped across the Darien Gap and the very first part of Columbia in an attempt to keep screw worms out of Central and North America.

And yet despite all the success that you talked about Erin in twenty sixteen, I think is when the first like rumblings that things were not all perfect began in modern most modern times, because there was an outbreak in Key West, Florida.

Right it was relatively quickly contained, but the deer population in Florida took a hit because of this.

And despite the incredible successes of the program, the truth is that New World screwworms are still present.

This fly is still present throughout nearly all of South America, as well as many islands in the Caribbean, including Cuba, Haiti, and the Dominican Republic.

And so since twenty twenty three, so in the last two years, cases have increased within like North and Central America from an average of about twenty five cases per year to six thousand and five hundred in one year in twenty twenty three.

Okay, And so since twenty twenty three, flies have been reported in Belize, Costa Rica, El Salvador, Guatemala, Honduras, Nicaragua, and Mexico, with more than twenty thousand new outbreaks reported like individual outbreaks as of August twenty second, twenty twenty five, per the World Organization of Animal Health, the World Okay, most all of these outbreaks are in livestock animals.

There are some cases in domestic animals.

There have also been cases in humans, but some of these outbreaks have been hundreds, if not thousands of animals infected.

So right now on the APHIS website, which is the Animal and Plant Health Inspection Service as of September second, twenty twenty five, there are several outbreaks ongoing in Mexico that are of serious concern to the US government, which has resulted in the US government shutting down all live livestock like live cattle trade between Mexico and the US.

There have been over five thousand, five hundred total cases in Mexico currently as of September second, seven hundred and seventy seven active cases and at least one confirmed case in a human in the US, which was a travel associated case with someone traveling from Al Salvador and coming back with an infection they've recovered.

In twenty twenty four, in Costa Rica, there were seven human cases that were reported, including one death, and in Nicaragua, there were one hundred and twenty four cases in humans in the last year.

But this is not the case that we as humans need to start panicking that we're all going to be infected with screwworm.

That's not the situation here.

But what this does show us is the fragility of our eradication efforts and the necessity of these one health approaches, and that they don't face the kind of budgetary cuts that we see currently playing out across every single health agency in the.

US budgetary and like intellectual cuts.

Yes, I have a question about so in terms of the numbers, we've talked about humans, we've talked about livestock, maybe a little bit of like domestic animals.

What about wildlife?

Great question, what about wildlife?

Certainly some of these infections are happening in wildlife, but we just don't have as good a numbers on wildlife populations.

Okay, but that is definitely a huge concern, right because not only is that like a potential reservoir, but it's also just then we're affecting livestock populations and like the effects of this eradication program on benefiting the health of wildlife should not be understated as well too.

Yeah, so that's kind of like where we stand with like what's going on with current with current outbreaks.

The live cattle market in the US was valued in twenty twenty three at three billion dollars per year, and it's gone up since then.

And the USDA says that estimates currently that an outbreak, like a true outbreak of screwworm in the US, could end up costing something like ten billion dollars in losses.

So this is this is something that I kept coming across to was the screw worm eradication program, which has cost money.

Cost money.

It costs million dollars a year.

Yeah, it has saved so much in terms of revenue from livestock people's livelihoods, And I think, what is like so it's like, okay, well we can do this.

We did this here in the US, we did this in Mexico, we did this throughout a lot of Central America and in South America.

It's like, well, they couldn't afford these programs, but they are losing money year after year.

And so it's like again it comes back to this, has this is an area wide program.

I lack the words the articulation needed to express this, but like this should be a continental a hemisphere effort one.

Hundred and so right now what the US is doing is going absolute ham They are reopening facilities in Texas, they are rebuilding a facility in Mexico.

They're going to spend tens of millions of more dollars to start breeding flies in the US and Mexico for sterile insect technique.

It is going to take years, at least eighteen months is the current estimate for these to happen and get up and running.

This is essential that it happens right now.

And they have this like five point plan which all sounds very much like war language.

But they are taking this very seriously.

And I think there was a paper from two thousand actually that really exemplified what is the true kind of hero of the screwworm story, and that is that in order for the success that we have had thus far to happen, a ton of cooperative agreements had to exist between countries for this eradication program to take place and to be successful, because yeah, flies don't give a crap about our national borders, the same way that infectious diseases like COVID don't honor these artificial divisions.

Even though this program is currently kind of at risk right and we're having to re up it.

It was only.

Possible in the first place because countries decided it was important enough to invest in and to work together, despite the difficulties and the financial agreements that had to be made to coordinate the implementation of this program, but they agreed it was important because they could make a lot more money.

I mean, and because the vustock industry.

Yeah, the livestock industry and the funding around this were considered important enough.

The absence of these screw worms in the US is estimated at least at a minimum to be a one point three billion dollar benefit every single year, So spending a few million dollars to keep this program running is nothing compared to that benefit.

It would be great if we could recognize that this is also true for so many other things besides just screwworm, and yes, expanding this to be able to eradicate it throughout its entire range rather than just stopping at the border of Columbia would go a really long way to improving the lives of humans and livestock and wildlife.

Across the entire western hemisphere.

Yep, uh huh.

And it is also possible that this could happen for Old world screwworm.

They have very similar mating habits, so they could also benefit from sterile insect technique programs.

But there just hasn't been as much of this collective agreement, infrastructure build up, and the money upfront to be able to do this where Old World screwworm, that's really hard for to say, is endemic, and so the programs that have tried to get up and running there have not been as successful.

There's a lot of interest too in like creating like newer techniques to make this even more effective and even more cost saving, like doing transgenic flies so that you're only really rearing male flies, because right now you're rearing indiscriminately female and male flies.

So if you could kind of whittle down the female population so that you're only releasing male flies, you're kind of doubling your efforts but at a lower cost.

But like all of that is amazing.

This is an amazing program.

It is incredible.

Let us apply this success to other facets of.

Public health, use it as a framework.

Like this, I mean and it is like it's it is.

But it's also not.

Yeah, and that screw worm baby.

Oh wow, what a fascinating thing.

Though, like also just fe like the entomology of it all.

I love the entomology.

I just also I love I think this is when I was like, oh, I could spend weeks just digging around on the USDA, like the National Agricultural Library website, and that the archives, the Internet archive.

Like I was having a blast looking through these oral histories and the transcripts, and I'm like, there are more that aren't digitized.

I want them.

I reached out to a library and was like, can you help me find this?

And they did, and I'm just like, I love library.

I love libraries.

I love librarians.

It's and also I think I had no concept how huge this program was because you can't find a lot of other agricultural well maybe agricultural pest videos, but like other disease videos from the nineteen fifties and sixties and so on, not so much.

Like this is a huge effort and it was a huge success story and it can still be Yeah, and it will be.

I think it will be successful.

The funding is going there.

It's happening.

Yeah, but yeah, can it go further?

That would be cool, That'd be cool.

Should we tell the people where they can find more information?

Should okay?

Should I have linked to all of his videos?

Love it?

I have a ton of sources, but I'm going to shout out too in particular.

So one was the website the Stop screw Worms.

It's a it's an online like digital collection, so it's selections from the screwroom Eradication Collection on the National Agricultural Library USDA websites.

Very cool.

And then also there was fun, a couple of fun chapters in a book, a popular book published in nineteen eighty four called The Dragon Hunters by F.

Graham, And it was these two chapters that I read focused on a screwroom and screwroom eradication.

Love it.

I had a bunch of papers I don't even know erin.

The one that I mentioned already that I did really enjoy was by Wiss from two thousand called screwworm Eradication in the Americas that focused a lot on like the success of these collective agreements and things like that.

There was also a paper from twenty seventeen that was review of research advances in the screwworm eradication program over the past twenty five years that was really interesting.

And then a couple of papers that are like quite old from like the eighties and nineties about the screw worm behavior and biology and things like that.

And then I also have links to the USDA website where they have their new World Screwworm Domestic Readiness and Response Policy Initiative document which is really interesting to read through.

And then also the updates if you would like them, because I'm sure the numbers will be different by the time that this episode comes out, But on the APHIS website you can find those, like updated data on what the outbreaks look like in Mexico, what other cases have been reported, and things like that.

You can find it all on our website This podcast will Kill You dot Com.

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Well, until next time, wash your hands you feelthy animals

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