Texas braces for an imminent screwworm infestation, a threat to the state’s cattle industry

Sign up for The Brief, The Texas Tribune’s daily newsletter that keeps readers up to speed on the most essential Texas news.

---

McALLEN — Multiple efforts are underway to stop a parasitic fly from swarming Texas and the rest of the U.S. and wreaking havoc on the nation’s multi-billion-dollar cattle industry.

As screwworms fly closer to the southern border, the U.S. Department of Agriculture has again suspended live animal imports from Mexico. Meanwhile, U.S. Sens. John Cornyn and Ted Cruz of Texas and Sen. Ben Ray Luján of New Mexico are trying to fund a nuclear facility that would stop the fly from further spreading. U.S. Rep. Tony Gonzales is leading a similar effort in the House.

The screwworm, a fly that embeds its larvae into the living flesh of animals and humans, has spread through Central America, including Mexico.

There is an increasing alarm that the fly could reach South Texas as soon as June, disrupting a $15 billion cattle industry.

“We're going to do our very best as an industry and as government officials working alongside us to make the outbreak stay wherever it’s found,” said Tracy Tomascik, Texas Farm Bureau associate director of Commodity and Regulatory Activities. “But the chances of the outbreak spreading out beyond South Texas are pretty high.”

The last time the U.S. saw an outbreak of this magnitude was in the 1950s. It took decades, billions of dollars and a significant international effort to beat the worms back. Farmers and ranchers worry the fly will disrupt the food supply in the U.S., another shock to the market following the avian flu that sent the price of eggs soaring.

And experts say the fly can attach themselves to humans and family pets as well.

The Senate bill would allocate federal funding to create a facility capable of making sterile flies that would kill the screwworm population. It was introduced last week and has a long way to go before it receives approval. Texas farmers worry the facility won’t be constructed and operational soon enough to prevent an outbreak.

“This is going to be catastrophic for the areas where this screwworm fly ends up infesting to any large degree,” Tomascik said.

Major industry threatened

The immediate effects of the cattle blockade have been good for ranchers like Giovana Benitez from Edinburg. She said the short supply of cattle has driven prices up for native cattle.

Texas is home to about 12 million cattle and calves, the largest population in the U.S., and is an industry valued at about $15 billion. But their numbers have been in decline. In 2023, the number of beef cattle shrank to 4.1 million head, the lowest since 2014, though their numbers slightly increased last year, according to a report from the USDA released in January.

Benitez knows the long-term effects of screwworm could be devastating.

Unlike a regular fly whose larvae stick to dead tissue, a screwworm fly prefers warm bodies.

They “land in a wound, lay their larvae while the animal is alive and the larvae will eat live flesh,” said Warren Cude, a Texas rancher and board member of the Texas Farm Bureau. “They're just eating a big hole in the animal until they kill it.”

Screwworms don’t affect the quality of the meat, but could devastate the available supply. What meat Texans find in supermarkets will be safe, but expensive.

"It's going to get to a point where we're not going to have enough cattle or people are not going to be able to afford to buy steaks or meat because it's going be a luxury,” Benitez said.

In preparation, Benitez is deworming all her cattle, as well as adding minerals to the feed and tagging the cattle for fly control.

She fears it won't be enough.

"I think we're not prepared,” she said, adding the industry doesn’t have the same level of people working in agriculture as it did during the last outbreak in the 1950s.

Eddie Garcia, the owner of Gulf Coast Livestock Auction, worries that the screwworm spread might prompt the Texas cattle industry to be cut off and lose market access to states like Oklahoma, Kansas, New Mexico and Louisiana where Texas cattle are typically shipped.

Garcia also expects the prices of live cattle futures will plummet in the trading market over the several days following an outbreak in South Texas but will stabilize once the industry receives guidance from the USDA.

"The worst thing about this whole screwworm is that it is going to affect the lifeblood of the industry, which is the cow-calf producer," he said, referring to the breeding of cattle.

Garcia said it is the foundation of the industry but it is also where screwworm can affect cattle the most because the fly can affect the wet navel of the calf.

“That is ground zero in this business,” he said.

Texas’ wildlife economy may also be devastated.

Deer hunting is a multi-billion-dollar industry in Texas, according to the Texas Wildlife Association. There are approximately 5.3 million wild deer in Texas. More than half a million hunters spend $2 billion annually to hunt whitetail deer. Landowners spend another $2.5 billion each year.

Texas will struggle to sell hunting licenses, firearms, ammunition, clothing, and anything else associated with hunting if those populations are ravaged as Dr. Chris Womack, a veterinarian from San Angelo, expects.

“The ripple effects there can be enormous,” he said.

Spreading quickly

Screwworms were a massive issue for U.S. farmers in the 1900s.

Outbreaks continued to occur until scientists learned how to sterilize males using nuclear radiation and stop the flies from reproducing. Using this technique and several facilities across the U.S. and Mexico, the flies were successfully beaten back south of Panama.

Relationships between the U.S. and South and Central American countries, like Panama, were the catalyst for overcoming historic screwworm outbreaks.

They created the Panama-United States Commission for the Eradication and Prevention of Screwworms, also known as COPEG. The facility established a barrier between South America and Central America that the screwworms were unable to penetrate for decades.

But in 2020, cracks in that barrier began to show. Inspectors who, up until that point, prevented animals infected with screwworms from migrating into Central America, had to be quarantined because of COVID-19, Womack said.

Then, the unmitigated migration of farm animals from South to Central America allowed the flies to spread further north.

By the end of 2024, the U.S. began calling on Mexico to take larger steps to stop the spread of screwworms. In November 2024, the U.S. banned Mexican cattle from entering Texas. That ban was released in February when Mexico promised to implement new inspection protocols that would stop the spread of screwworms. In another reversal, U.S. Agriculture Commissioner Brooke Rollins closed the border May 11.

In April a group of Texas agriculture experts visited Panama to determine what was happening with the screwworm. Womack bought an airline ticket and tagged along, he said.

What he learned was worrisome.

Beyond COVID-19 and the migration of people and animals across the continent, there was an overwhelming loss of generational knowledge. Central American countries were left without any guidance on how to prevent the spread, Womack said.

Producers were processing cows or calves without treating fresh wounds to prevent infestation, and many don’t know to look for screwworms.

“I read reports of Mamas laying their infants down in the shade of a tree, without knowing they needed to provide protection from the flies,” he said. “The flies blow up the nostrils of the babies and kill them. Was that knowledge written down anywhere? Probably not.”

By February, Nicaragua confirmed screwworms had entered human hosts. In Costa Rica, these infestations have led to deaths.

The solution: a proposed facility

Countries must do what they can to educate animal producers and wildlife managers about what to look for and proper protocol if screwworms are discovered, Womack said. There are proven methods to eradicate the bugs.

To beat them back to South America, there also needs to be a significant investment in a sterilizing facility on U.S. soil, experts say.

“Hopefully, we can start production or development of this facility as soon as possible because we simply don't have enough sterile flies to even deal with the outbreak,” said Tomascik, of the Texas Farm Bureau.

A sterilizing facility would take an act of Congress to make a reality. The facility would need to be secure from the ground up to prevent the screwworms from escaping and causing the spread to happen faster. It would also need to be able to cope with Cobalt, a nuclear material, to radiate the bugs.

Tomascik wants the U.S. to work quickly, but mindfully, he said. Cutting corners could worsen the problem rather than solve it, he said.

The STOP The Screwworm Act would allocate funding and permit the USDA to begin construction. The bill was introduced to the Senate on May 14 and referred to the Committee on Agriculture, Nutrition and Forestry.

“We don't have 18 months or two years. We need it done,” Cude said. “They needed to be pouring concrete last week or last year.”

Disclosure: Texas Farm Bureau and Texas Wildlife Association have been financial supporters of The Texas Tribune, a nonprofit, nonpartisan news organization that is funded in part by donations from members, foundations and corporate sponsors. Financial supporters play no role in the Tribune's journalism. Find a complete list of them here.

---

First round of TribFest speakers announced! Pulitzer Prize-winning columnist Maureen Dowd; U.S. Rep. Tony Gonzales, R-San Antonio; Fort Worth Mayor Mattie Parker; U.S. Sen. Adam Schiff, D-California; and U.S. Rep. Jasmine Crockett, D-Dallas are taking the stage Nov. 13–15 in Austin. Get your tickets today!