The New World Screwworm continues to advance north through Mexico, toward the Texas border.
Screwworms are parasitic flies that were once devastating to ranchers, since they lay their larvae in the open wounds of animals like cattle and sheep. The larvae then burrow down into the skin of the animal, often causing infection and even death.
Researchers pushed screwworms out of Texas by the 1970s. Now that they are on their way back, agriculture leaders and lawmakers are scrambling to protect the state’s multibillion-dollar livestock industry. The Texas Standard’s Michael Marks rounded up the updates on screwworm response.
This transcript has been edited lightly for clarity:
Texas Standard: Screwworms haven’t been an issue in Texas for decades. Can you quickly remind us why they’re on ranchers’ radar again?
Michael Marks: That’s right, they haven’t been a problem for American ranchers since the ’70s. These are little flies that their larvae, they’ll actually eat into the host. They screw down in there; that’s why they’re called screwworms. They can cause gnarly infections and death in some animals.
They weren’t a problem for a long time because researchers at the USDA came up with this method to eradicate them. They built these big industrial-sized plants to manufacture sterile male screwworms. They sterilize them with nuclear radiation.
These would get dropped out of airplanes into screwworm populations and suppress them. This was so successful that entomologists used the method to push the flies all the way down to Mexico, Central America, to the border of Panama and Colombia. They had a barrier of sterile flies there.
That worked for decades, but in 2023, the screwworm somehow slipped through. They have been heading north toward Texas ever since.
How close are they to Texas right now?
Less than 400 miles, which means they’ve already traveled more than 1,500 miles north. The big problem to halt their progress is that there’s only one facility in the world that makes these sterile flies, and that’s just not enough.
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So then what’s being done to prevent them from reaching the U.S., if you can’t get these sterile flies?
People are doing all sorts of things, David. So one thing that’s happened is the U.S. Department of Agriculture stopped accepting imports of Mexican cattle a few months ago. They thought they might be able to resume that by August, but we’re in August and they have not done so.
It’s also USDA putting up money for a sterile fly dispersal facility at Moore Air Base in the Rio Grande Valley outside Edinburg. So if the flies do reach Texas, there will be a staging area, you know, close to the border to fight them.
You know, I mentioned earlier making more flies. That’s the big problem. Earlier this week, Senator John Cornyn of Texas said he planned to ask his colleagues for more support in this area to get a new sterile fly facility built.
“As the New World Screwworm continues traveling north, we need another plan to prevent population spread,” he said. “A sterile fly plant will cost as much as $300 million, according to some estimates. And that’s certainly not just pocket change, but it pales in comparison with the cost of not doing anything to eradicate.”
It would probably take three or so years to get that plant up and running. So meanwhile, the governments of Mexico and the United States, they’re spending $21 million to retrofit a fruit fly production facility in southern Mexico to make more screwworms in the interim.
This is phenomenal. Okay, so what happens, though, if those screwworms do end up reaching Texas? What are the options then?
Well, it’s going to be a big problem for folks, a big nuisance. Anyone involved in livestock is going to be feeling it if they get reestablished here.
I’ve talked to some ranchers who dealt with screwworms when they were here several decades ago, including John Kearney, who worked cattle at his father’s ranches outside Weimar.
“I remember many trips out here with Dad, just running and making the rounds checking every cow,” he said. “And so it was an everyday vigilance kind of thing.”
You’ve got to be out there checking your cattle, doctoring them if they’re sick or have the flies.
And of course, it’s not just cows. Another industry that’s spooked by this is the whitetail deer breeding business, which depends on large volumes of mammals. Agriculture Commissioner Sid Miller said his department is going to set out a bait called Swormlure-5 in traps along the Rio Grande in order to help mitigate the problem. We’re still waiting for more details on that.
But the state has also set up a coalition with groups like the Texas and Southwestern Cattle Raisers Association, Texas Parks and Wildlife, the Animal Health Commission, all working together to solve the problem, keep folks informed. Their website is screwwormtx.org, where people can check out updates, that sort of thing.
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