By Stephen Marcantel
The Advocate
In an old coal-mining town in northern Texas, around 130 miles from Dallas/Fort Worth, Greg Buenger raises beef cattle on his ranch. But Buenger, also a Texas Farm Bureau District 3 state director and retired veterinarian, has his eyes elsewhere at the moment, far from the northern flatlands.
His focus is on the Texas-Mexico border, where a series of cases involving the New World screwworm have been documented.
The screwworm is a larva of the Cochliomyia hominivorax fly that can invade the tissues of any warm-blooded animal, including humans. The parasite enters animals’ skin, causing severe damage and lesions that can be fatal. Infected animals are a serious threat to herds.
The parasite is typically found in South America and the Caribbean, but since it escaped containment in Panama in 2023, it has been steadily moving northward. The most recent case was found in a cow near the Mexican state of Nuevo Leon, 70 miles from the border with Texas
The U.S. Department of Agriculture calls it a “devastating pest” and said in June that it poses a threat to “our livestock industry, our economy and our food supply chain.” The federal government had been expected to spend hundreds of millions of dollars to keep it out of the United States.
"There's so many dynamics and so many scenarios that equate to financial loss and hardship," Buenger said. "I think folks — politicians anyway — are going to be a little surprised at the economic impact of this."
What is a screwworm?
Screwworm is the parasitic larva of the screwworm fly and is a type of blowfly. Think the metallic, oil-slick colored flies that bother picnicking families.
There are two types of screwworms: Old World and New World.
The Old World screwworm larvae dine on the decaying and dead flesh of warm-blooded animals and are generally considered unimportant.
New World screwworm, or NWS, on the other hand, feeds on the flesh of living warm-blooded animals. The flies lay up to 3,000 eggs throughout their two-to-three-week life on the outside of open wounds and mucous membranes of animals, Buenger said. The larvae then burrow into the flesh and feed before turning into pupae, dropping to the ground to mature and start the cycle again.
If the animal — cattle in Buenger's case — goes untreated, the results can be fatal.
"Quite often, they will kill the animal. In fact, that's almost always the result, depending on where the wound is," he said.
New World screwworm once was a problem in the U.S., but was eradicated in the mid-1960s, according to U.S. Department of Agriculture documents. Using a technique discovered in the early 1950s, sterile male flies were produced to breed with female flies using dispersal facilities that the U.S. used to have in places like Texas and Florida.
Those facilities closed after the threat subsided.
The U.S. and Mexico collaborated to push the NWS south into Panama, where it remained until 2023, according to Louisiana Department of Agriculture and Forestry Commissioner Mike Strain.
So far in Mexico, over 7,000 New World screwworm cases have been reported, Strain said. The closest case was an infected cow found in late September in Sabinas Hidalgo, Nuevo Leónr, with San Antonio the closest major American city. Prior to that, cases were discovered in Mexico City.
The flies can travel up to 12 miles a day without wind, but Buenger believes the New World screwworm will likely enter the U.S. via a trailer, illegal movement of animals or through wildlife.
The increasing threat has led USDA Secretary Brooke Rollins to close the border to imports of livestock and beef from Mexico. The initial closure began in July but was lifted several times before ultimately closing again. The border remains closed to imports. Mexican agricultural Minister Julio Berdegue is set to meet with Rollins next week to discuss reopening the border to Mexican cattle, according to Reuters reports.
Impacts on industry
The impacts on Texas and, by extension, Louisiana's cattle industry could be significant if left unchecked.
In Texas alone, the largest cattle-producing state in the U.S., a 1976 outbreak of New World screwworm cost the 2024 equivalent of $1.8 billion in total economic loss, with $732 million of that hitting producers in a single year. That is more than the entirety of Louisiana's $640 million cattle industry, according to 2023 LSU Ag Center data.
The eradication of NWS is believed to have benefited producers by an estimated $796 million annually and $2.8 billion toward the broader economy, according to USDA documents.
Border closures have already affected Texas cattle ranchers, who rely on livestock from Mexico. The impact is also being felt in Louisiana.
Beyond cattle and livestock, if the screwworms were to enter Texas and Louisiana, local deer populations would be devastated, with around 80-90% of the population under threat of being killed, Strain said.
That would have a huge impact on a state known as Sportsman's Paradise and on an industry that contributes more than a billion dollars to the local economy, said the Louisiana Department of Wildlife and Fisheries' Assistant State Wildlife Veterinarian Rusty Berry.
"It's a really big deal, and we're going to spend hundreds of millions of dollars trying to keep this pest below our borders," Strain said.
What is the U.S. doing?
Experts acknowledge that keeping the border closed will likely only slow the northward spread of the screwworm.
The next step is what worked to eradicate flies in the U.S. in the 1960s: sterile fly facilities, said Christine Navarre, an extension veterinarian and LSU AgCenter professor in the School of Animal Sciences.
The USDA, in a joint effort with Mexico, is investing nearly $30 million to renovate a sterile fly facility in the Chiapas State, according to New York Times reports. The agency is also investing $750 million in a screwworm protection facility in Texas, according to Texas Gov. Greg Abbott.
The plant in Mexico aims to be ready by July 2026 and would double the number of sterile flies Mexico can release into the wild, according to Reuters. The Texas facility is years away from being built, Beunger said.
"We have no defense with flies yet, other than ones we can fly up from Panama," he said.
Currently, the only sterile fly-producing facility is in Panama, but it can only produce about 20 million a day, Strain said. The U.S. is hoping for something on the scale of hundreds of millions a week.
There are precautionary steps and protections that ranchers and the state can take.
For one, ranchers should consistently be on the lookout for wounds in their herd. When wounds are noticed, they should be treated immediately. If screwworms are found near the wound, ivermectin or Dectomax injectables can be used to kill off parasites.
It's something Lee Robbins, an Angus beef seed cattle rancher near Unionville in north Louisiana, has been on top of, taking time to look over his herd.
"We've just been a little more vigilant over the past few months after seeing the reports, as it gets closer and closer to the southern border. Is it a major concern, immediately? No. Longer term? Yes," Robbins said.
Robbins said the New World screwworm hasn't entered much of his conversation with Louisiana ranchers, but some of the Texas Panhandle ranchers he knows are starting to mention it.
"Once it hits that borderline, it's going to change," Robbins said.