How Millions Of Flies Can Help Stop The New World Screwworm

FLORA LICHTMAN: This is Science Friday. I’m Flora Lichtman. A bit later in the hour, how climate change is upending the home insurance market and the science behind death by poison, Agatha Christie style. But first, an unwelcome pest has cattle ranchers, entomologists, and the federal government on edge, the New World screwworm fly. This fly was technically eradicated from the US back in the ’70s. But now an outbreak has been creeping further and further north into Central America and Mexico, inching towards the US border.

This fly is notorious for laying eggs in the wounds of animals and slowly eating its victims from the inside out. But scientists have a strategy to stop the fly, and it involves dropping millions of bugs out of airplanes. Here to tell us more is Dr. Sonja Swiger, Entomologist and Professor at Texas A&M. Sonja, welcome to Science Friday.

SONJA SWIGER: Thank you.

FLORA LICHTMAN: Tell me more about these screwworms. Are they as horrible as they sound?

SONJA SWIGER: Yeah, they actually are. So as entomologists, we do try to control pests when we can. But it’s not usual that we try to eradicate these pests completely. And this is one of those that we felt just had to be eradicated to basically better the world, so to speak. So yeah, it is definitely a very bad insect to have around.

FLORA LICHTMAN: Why do they need to be eradicated?

SONJA SWIGER: The main reason is their impact to the industries. Of course, cattle being a huge industry for the United States, and other livestock as well, but it’s not just them. These flies will lay their eggs in all warm-blooded animals.

So that’s basically everything, right? And that includes dogs, that includes cats. When we had an outbreak in the Florida Keys back in 2016, they had a raccoon, they had a cat, they had a dog, they had a pig, and all these other animals, plus the deer, that were infested with these flies. So they will attack a number of animals, including humans, which isn’t common, but it can happen.

FLORA LICHTMAN: OK, so they’re moving north towards the US. What is your level of alarm?

SONJA SWIGER: It’s definitely a concern, right? We have been able to maintain them at the Darién Gap, which is a small area, geographically speaking, of the Eastern side of Panama. And they’ve stayed over on that side for over 30 years. So keeping them down there made it easier to contain them, lowered the impact to areas, of course, that we do not want them in. So the fact that they have moved out of that area and are now significantly moved further north than what we would really like them to be, it does put us on edge just a bit and does make it a very big concern.

FLORA LICHTMAN: So where is the management program happening now? Is it in the US yet?

SONJA SWIGER: It’s in Mexico. So the United States funds that program. And obviously, the flies were being managed and maintained in Panama for, again, 33 years with no concerns. But since this issue has happened, they’re dropping and releasing those flies at the most northern point.

So we just recently had an announcement that they found another case further north. So I’m sure that all efforts are now being put into that area. Prior to that, they were all being dropped around the Oaxaca-Veracruz area of Mexico.

The way they do that is they literally drop the actual adult flies of the plane. They release them as they fly over. And then they also have these stations on the ground where they will place several thousands of pupa, and then they will hatch in that area. And they usually put those in places where they have a confirmed infestation or an animal that has larva present on them in that area.

FLORA LICHTMAN: Tell me the history of these flies, our relationship with them anyway.

SONJA SWIGER: Well, they’ve been around a long time, right? So we call them New World screwworms. So everybody kind of gets to saying, oh, this is a new pest. But that’s not how it really works.

There’s two species in the entire world that are known to be of this nature. And one lives on our side of the world. And the other lives on the other side of the world, over in Africa and Europe and other countries. And it’s called the Old World screwworm. So that’s why ours is called the New World screwworm, based on old histories and coming to the New World.

So they’ve been here a long time, back into the mid-1800s. And as our industry started to grow in the livestock side and we saw the impact of this fly, it was felt that they needed to be managed. And the way to manage them, of course, was with that eradication program.

FLORA LICHTMAN: What’s the program like now?

SONJA SWIGER: The program is very similar to what it was when they started it. So the program was developed back in the early 1900s. So around the 1930s into the ’50s, there were scientists that worked with USDA that developed a system on how to manage these flies.

And part of fly management is understanding flies. And in order to do that, they had to learn how to grow the flies, which sounds a little funny. So we basically grow them inside a laboratory in order to understand them better, and then also to kill them, which is a unique concept. But that’s how entomologists have to work so that we have populations we can basically handle.

FLORA LICHTMAN: OK, so they’re mass rearing them. But then, how does that help manage them?

SONJA SWIGER: Once they’ve figured out proper ways to grow them in large numbers, they then had to figure out a way to, of course, control them in large numbers. And the way that they came up with this fly was with a radiation program. So when they hit the pupa stage, they radiate them with the processes. And they’ve changed the procedure of the radiation since the 1930s till now.

And when they do that, it basically destroys them in a genetic fashion that prevents them from producing future offspring. So that makes them sterile. The reason it works for this fly and not other flies, which has always been a question, well, why do we do it for this one and not these blow flies or these houseflies or all these other flies, is because this species is known to only mate one time in their lifetime. And that’s unique to this fly, as opposed to houseflies, which will mate with multiple males, and then produce multiple offspring.

FLORA LICHTMAN: OK, so you radiate the flies, you make them unable to have offspring, and then you dump all of these radiated screwworm flies in the areas where they’re living. And you’re hoping that they mate with the wild ones, basically.

SONJA SWIGER: Correct, and this species of fly in nature doesn’t have large numbers. Now, when they’re around, they’re a significant impact. But they don’t have large numbers. They will make millions of flies in the lab, and then they will dump all those flies in one area.

And what you’re doing, you’re oversaturating the wild population with these now sterile males in hopes that these males will be found by those wild females. And then, as they keep mating with the sterile males, they think that they are bred in order to lay eggs. And they do lay their eggs, but they lay eggs that don’t hatch.

FLORA LICHTMAN: Right, are there unintended consequences of dropping millions of flies?

SONJA SWIGER: No, not of this species. Again, we’ve been doing this program basically since the 1950s. Since they’ve started it, they’ve never really had any hiccups with it. They’ve never had any backfiring of it because these flies do not mate with other species.

These insects, particularly, are not playing a viable role in any ecosystems, so taking them out doesn’t impact anything else. And it actually saves the lives of animals and saves the lives of humans. And if you find some of our farmers who were around back in the day when they did it here in Texas, because Texas was the last state that actually got rid of it, so there were folks that are still farming today that remember doing this back in the ’70s. And then I have a lot of guys I talk to that remember going out with Grandpa to find these flies. And it’s fun to hear the stories.

FLORA LICHTMAN: OK, so we pushed this fly out of the US decades ago, why are they creeping back up north?

SONJA SWIGER: So that’s really tough to pinpoint. One of the issues is mild winters, because this is a species that is tropically based. It doesn’t do well in cold temperatures. But as you have consistent, mild winters in an area, that can expand its range.

Movement through the Darién Gap has also been noted as a concern. And this is both movement of people, and people and animals, and probably lack of knowledge, in addition to probably some lack of surveillance. But as you bring people through an area that may not be aware of an impact of a pest, and they’re not teaching them about that pest, obviously you have a lack of education. And then things get moved around that we may not wanted to have move around.

FLORA LICHTMAN: It’s like these diseases that we’ve all but wiped out but are recurring now. And doctors aren’t familiar with them. It sounds similar.

SONJA SWIGER: Yeah, and that’s what happens, right? We do so good, and we clear things up. But then we forget to talk about them in the future. And then people forget what they are. And I know that right now, education is definitely a very important tool that we can use to our effects, because we need to tell people what this thing does and have them prepared.

FLORA LICHTMAN: Is this the kind of thing that you read about in textbooks when you were studying?

SONJA SWIGER: It was. When I was in grad school, it’s like one of our shining lights. Ooh, look what we did as entomologists and veterinarians, we eradicated this New World screwworm, and how terrible it was, as well as a tick species that we got rid of. But they have actually come out of the textbooks. And I’m a little sad about that because I preferred them staying in black and white.

FLORA LICHTMAN: There’s been coverage of this in the news. And the headline is like, millions of bugs might be dropped over Texas.

SONJA SWIGER: Yes.

FLORA LICHTMAN: How’s the public responding?

SONJA SWIGER: It’s interesting. As usual, you want to avoid Facebook comments, but–

FLORA LICHTMAN: Yeah, always.

SONJA SWIGER: As always, but it’s hard not to. I’ll look at a few, and then I have to just step away. But–

FLORA LICHTMAN: Wait, is that because there– what is the concern? Are there conspiracy theories about it? What’s the concern?

SONJA SWIGER: There is. There’s a lot of conspiracy theories. And of course, it’s made up by the government. It’s another scare tactic.

And again, it’s just lack of education. And most folks don’t anything about it. I mean, I didn’t learn about it until I was in grad school to be an entomologist. So it is kind of like out of a sci-fi movie because it’s such a freaky insect that you think, this can’t be real. But it is real.

FLORA LICHTMAN: I mean, you say it’s a freaky fly.

SONJA SWIGER: [LAUGHS]

It is.

FLORA LICHTMAN: For an entomologist to say, that’s real. Things are getting real. What elevates it to freakdom for you?

SONJA SWIGER: Well, I mean, the way that it prefers to grow its larva. Blowflies in general are cool group of insects. I actually kind of like blowflies. I studied them in grad school.

But their role is as decomposers. They come in, they clean up a carcass, which is a disgusting thing to think about. But somebody’s got to do it. So we’re happy they’re there and want to do that for us.

But this one decided to be a little different and decided to make the carcass, which means it lays its eggs, when you’re still alive, on the body. And that’s kind of freaky. I mean, it’s never good to actually be eaten by an insect. And that’s one of those things that creeps people out anyways.

FLORA LICHTMAN: I agree.

SONJA SWIGER: Even though it doesn’t normally happen.

FLORA LICHTMAN: Completely agree. OK, what’s your message? Is there anything you want to leave the public with?

SONJA SWIGER: Yeah, I mean, I think it’s important that people do some research, look it up, and realize that this is a real insect. We do target talking to livestock folks, because we know people who own cattle and other livestock are going to be impacted. So we just want people to be aware, to understand its importance and the significance and the reason why we need to keep it out of the United States.

FLORA LICHTMAN: Thank you, Sonja. That’s about all the time we have. I appreciate you coming on to talk.

SONJA SWIGER: I appreciate it. Thank you.

FLORA LICHTMAN: Dr. Sonja Swiger, Entomologist and Professor at Texas A&M. Coming up after the break, why climate change is making it harder to get home insurance and which states are feeling it the most. Stay with us.

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