Follow the political blame game as a screwworm parasite threatens livestock in Texas

U.S. Agriculture Secretary Brock Rollins watched the release of sterile flies to fight the New World screwworm on Thursday and visited a Texas farm where one of the first cases of the pest was discovered. Screwworm could devastate the country’s livestock industry.

She later reiterated her assertion that the administration of former President Joe Biden is responsible for the return of the parasite to the United States six decades after it was eliminated. Democratic leaders say cuts to the nation’s agriculture agency under President Donald Trump are to blame.

Watch: News Wrap: 3 more cases of screwworm found in Texas and New Mexico

Rollins said screwworms are on track to become a billion-dollar international problem, but they can be contained if ranchers are vigilant, monitor their herds and other wildlife, and treat any infestations quickly. She pointed to the calf where screwworms had been found six days earlier in a wound where the umbilical cord was attached.

“He couldn’t be happier. He’s just hopping around the pasture,” Rollins said.

Screwworms are flies that lay their eggs in the wounds of warm-blooded animals and feed on living flesh rather than dead tissue. Scientists say releasing sterile flies to mate with females is the most effective way to control their numbers, a strategy that has worked for decades. A warming planet complicates efforts by giving screwworms, which thrive in hot, humid weather, more places to spread.

A multi-billion dollar response is planned to combat screwworms

The USDA is preparing to launch an all-out attack on the screwworm, which has been trapped in the narrow Isthmus of Panama for decades.

Regardless of the reason, bringing screwworms back south and keeping them out of the United States will be expensive. The USDA estimated it would spend more than $1 billion on efforts to save cattle and other livestock.

About $750 million will be allocated to build and operate a factory capable of producing up to 300 million sterile flies per week. This technique has been used for decades, as female screwworms mate only once, and if they choose a sterile mate, their eggs do not hatch, and the fly population dwindles.

Read more: What to know about the New World screwworm fly and its reappearance in the United States

The goal is to protect the American cattle industry. Experts believe this parasite should not cause an immediate increase in near-record beef prices as long as it does not turn into an outbreak and lead to the death of large groups of cattle. Screwworms do not affect food safety.

The parasite has already disrupted the Mexican beef industry. The United States closed its southern ports to Mexican livestock last summer.

Mexico has recorded more than 28,000 cases of screwworm infection since the flies returned two years ago, most of which were confined to the southern states. The Mexican government has halted the import of almost all live animals from the United States after the discovery of screwworms here.

Scientists are not sure how screwworms appeared again

The United States almost completely eliminated screwworms for sixty years, and scientists in North and Central America eventually brought them to a containment zone in Panama. But in 2023, the flies showed up and started heading north.

Experts say screwworms are here to stay at least through this summer. Seven cases have already been discovered in Texas and New Mexico. A 12-mile (20-kilometer) quarantine zone is established around each location where a case is detected.

While they work to find a solution, scientists say they are not sure exactly what caused the screwworms to leave the area where they were trapped in Panama.

“I don’t have an answer to that question, and I don’t know if anyone does,” said Jonathan Cammack, a professor of livestock entomology and parasitology at Oklahoma State University. “It doesn’t help us speculate.”

WATCH: Rollins holds update as USDA confirms more screwworm cases, including one outside Texas

The key now, he said, is to ramp up the sterile fly program and get international cooperation to bring the pests back to Panama.

Climate change is also helping the spread of screwworms, said Lee Haines, an assistant research professor of biological sciences at the University of Notre Dame.

“The fly is a warm-blooded creature whose entire life cycle, from egg to adult, can be completed in less than three weeks under tropical conditions,” Haines said.

Even Canada temporarily stopped importing cattle, horses or other livestock from Texas. The parasites prefer humid areas with temperatures of at least 77 F (25 C), and those days increase northward.

Democrats question cuts. Republicans blame immigration

While Rollins moved quickly to implement a $1 billion response to the screwworm outbreak, she also placed blame on the Biden administration, noting that it was in power when the parasite began moving north again.

She added, without showing any evidence, that the flies were with animals following migrants north, as well as boarding livestock and other animals sold by Mexican cartels outside regular markets.

“People moving north to America, bringing their livestock with them, the Mexican cartels trafficking illegal livestock, we knew it was coming,” Rollins told the U.S. Senate Agriculture Committee on Wednesday.

Read more: Screwworm fly discovered in Texas decades after livestock threat was largely eliminated in US

Nearly a dozen Democratic U.S. senators sent a letter to Rollins this week asking whether job losses at the USDA have hurt its food inspections and livestock safety programs.

Nearly 20% of counties in the United States that began 2025 with at least one employee from the Federal Plant and Animal Health Inspection Service ended the year without any, the letter said.

Rollins said she has moved more than 100 USDA employees to the screwworm response. She said it has been one of her top priorities since Trump chose her to lead the USDA.

But Democratic U.S. Rep. Ted Lieu of California said blaming Biden is shortsighted and shows once again that the Trump administration is creating problems with reckless spending cuts.

“The life cycle of the screwworm is approximately 14 to 54 days, depending on temperature and humidity. The Trump administration has been in power for more than 500 days,” Liu said earlier this week. “This is the responsibility of the Trump administration. They have to acknowledge it, and they have to apologise.”