A parasite that America spent five decades eradicating has come back, and the people who cut the program that kept it away are calling it an "all of government effort" to fix.

"Even though billions of sterile flies have been dispersed by USDA, the screwworm has still advanced over 1,100 miles from southern Mexico to Texas, and USDA has missed an important component."

— Sid Miller, Texas Agriculture Commissioner

The New World screwworm (Cochliomyia hominivorax) was confirmed in a three-week-old calf near La Pryor, Texas on June 3, 2026. It is the first time this parasitic fly has been detected in US livestock since 1966. The species name means "man eater." Its larvae feed exclusively on the living tissue of warm-blooded animals, and if left untreated, the host dies.

The screwworm was not always a problem in America. In the early twentieth century, it devastated cattle operations across the South. A single infestation could destroy an entire herd within weeks. The USDA spent more than five decades eradicating it through one of the most successful biocontrol programs in history: releasing billions of sterile male flies to overwhelm the wild population. Female screwworms mate only once in their lifetime. When they mate with a sterile male, they produce no offspring and die out.

By 1966, the pest was gone from the United States. Eradication continued southward through Mexico by 1991, then through Central America to the Darién Gap at the Panama-Colombia border by 2000. For decades after that, a single sterile fly production facility in Panama maintained a quarantine line that kept the pest out of North America. Occasional incursions west of the Panama Canal happened roughly 25 times per year and were quickly contained. It was one of those rare government programs so successful nobody remembered it existed.

Until 2023, the Darién Gap barrier held. Then it did not.

Max Scott, an entomologist at North Carolina State University who has genetically modified screwworm to prevent reproduction, said the failure was a combination of factors. The strain of sterile males being released had degraded over time and was no longer competitive with wild males. Migrant movements across the Panama-Colombia border carried infected animals northward. And critically, the funding that sustained the program began to dry up.

In March 2025, the USDA cut funding for animal disease control and prevention programs, including New World screwworm monitoring through the Food and Agriculture Organization. That funding had supported more than 180 outbreak investigations and responses across 22 countries. It maintained laboratory capacity in testing, biosafety, and workforce development specifically targeted at keeping screwworm from reaching the United States.

Hundreds of veterinarians, support staff, and lab workers at the animal health arm of the USDA left their positions under the Trump administration's push for resignations, according to sources familiar with the situation. The departures came as the agency was already managing its longest-ever bird flu outbreak. Fewer specialists remained to respond when the screwworm pushed north through Mexico.

Translation: the people who maintained the quarantine line were told to leave, and then the line broke.

The screwworm moved through Mexico rapidly despite USDA efforts. By May 2025, it had been detected in Oaxaca and Veracruz, roughly 700 miles from the US border. The USDA suspended imports of live cattle, bison, and horses through southern ports of entry. In August 2025, a Maryland resident who had traveled to El Salvador was diagnosed with screwworm infection. She recovered, and officials found no further transmission. But it was a warning.

USDA Secretary Brooke Rollins called the screwworm response an "all of Trump administration effort" during a briefing on June 3. She insisted there is "no reason to believe this incursion will result in establishment of the pest in our country." The agency activated personnel on the ground in Texas, established a 20-kilometer infested zone, and began releasing sterile flies from aircraft. A shipment of emergency-use treatment drugs was dispatched to South Texas.

Sid Miller, Texas Agriculture Commissioner, was less sanguine. He pointed out that USDA had developed a system called Swass (Screwworm Adult Suppression System) that uses attractants, bait, and targeted insecticides to reduce adult fly populations before sterile releases finish the job. "Swass was developed by USDA, tested by USDA, and successfully deployed by USDA to eradicate screwworm in Mexico and Texas when it last appeared," Miller said. "USDA already owns the playbook; the only question is whether USDA will use it before this situation gets worse."

The administration's response has been to spend money on damage control rather than address why the damage happened. In March 2026, Rollins announced a $750 million sterile fly production facility at the Moore Air Base in Edinburg, Texas, set to open next year. Earlier this year, the USDA allocated $21 million to renovate an existing facility in Metapa, Mexico.

The economic stakes are enormous. The Federal Reserve Bank of Dallas estimates that a full outbreak could cost the Southwest more than $3 billion. Texas A&M AgriLife puts the damage at $2.1 billion for the cattle industry and $9 billion for hunting and wildlife industries in Texas alone. That is on top of record-high beef prices that Americans are already paying.

In Mexico, where screwworm cases have surged past 6,500 in 2024, ranchers without access to commercial treatment have resorted to applying gasoline or lime to open wounds in desperate attempts to coax the larvae out. The USDA's own data from a 1972 outbreak showed 90,000 cases across the country. A recurrence of that magnitude would be catastrophic for an agricultural sector already under severe stress.

The screwworm does not pose a food safety risk. It is not contagious between animals in the traditional sense. Female flies lay eggs in open wounds, and the resulting larvae eat their way through living tissue. But it poses a massive food production risk. Cattle die untreated. Wildlife populations collapse. The 2016 outbreak on Big Pine Key in Florida caused significant mortality among male Key deer, an endangered species. Eradication that year came at great financial cost and only after substantial native wildlife loss.

The last time America faced this was when it had the staff, funding, and international cooperation to stop it. This time, those things were declared unnecessary overhead.

There is a word for what happened here. Recrudescence: the return of something terrible after a period of reprieve. It was widely considered the word of the day after Trump's election in 2024. Nobody seems to have applied it to parasitic flies, but the fit is precise.

The screwworm program was not expensive relative to what it protected. It was not ideologically controversial. It did not involve books or bathrooms or identity politics. It involved breeding sterile insects in a factory that smelled bad and dropping them from planes over Central America. And it was cut anyway, because the framework that governed the cuts treated every government function as equally expendable.

The question is not whether the USDA can contain this outbreak. The agency still has the technology and the playbook. The question is how many other things quietly stopped working while nobody was watching, and what they will cost when they come back.