Screwworm Returns
New World Screwworm Fly Detected in Texas, Posing First Cattle Threat in Decades for US
The New World Screwworm fly has been detected in south Texas — the first time in decades the flesh-eating parasite has threatened the U.S. cattle industry. USDA confirmed the case on June 3, 2026, after lab tests identified the fly's larvae in a 3-week-old beef calf on a ranch near La Pryor, Zavala County, about 50 miles from the Mexico border.
Agriculture Secretary Brooke Rollins called it only the third time in U.S. history the pest has appeared domestically, and said the government is ready. "The United States has defeated this pest before, and we will do it again," she said. Texas State Veterinarian Dr. Bud Dinges immediately established a 12-mile quarantine zone around the site, halting all movement of warm-blooded animals in the area, according to Associated Press.
A Parasite That Eats Living Flesh From the Inside
The New World Screwworm (*Cochliomyia hominivorax*) is not a typical maggot. Most fly larvae feed on dead tissue. This one burrows into living flesh through open wounds. It can kill an untreated animal within days. The infested calf in La Pryor had larvae in its umbilical area — a common entry point in newborns. Officials say the calf is expected to recover, USDA confirmed.
The U.S. wiped out the fly in 1966 using a technique called sterile insect release — flooding an area with millions of lab-raised flies that cannot reproduce. A "biological barrier" of sterile flies was then maintained in Panama to stop the South American population from moving north. That barrier broke down in 2023. Since then, the fly has spread through Costa Rica, Nicaragua, Honduras, and deep into Mexico, racking up over 144,000 confirmed animal cases, according to Texas Animal Health Commission.
A Year of Warnings Before the Fly Crossed Into Texas
The USDA saw this coming. Mexico detected its first case in decades in November 2024. By September 2025, a case was confirmed in Nuevo León — just 70 miles from Texas. The USDA suspended all livestock imports from Mexico on May 11, 2025, and Secretary Rollins announced a $100 million response plan in August 2025, calling the threat a "national security issue," per Brownfield Ag News.
USDA teams tested over 58,000 fly samples in the year leading up to this detection. They were already releasing 4 million sterile flies per week along the border region by air. On June 2, just one day before the confirmed Texas case, Rollins disputed a claim by Texas State Rep. Don McLaughlin that the fly was within one mile of the border, saying the nearest known case was 25 miles away in Mexico, according to Texas Tribune.
Quarantine Locks Down Ranchers While Sterile Fly Surge Begins
The 12-mile quarantine zone in Zavala County stops the movement of all warm-blooded animals — cattle, pets, and show animals alike. For local ranchers, that means no sales, no transfers, and no income from those animals until the zone is lifted. Dr. Dinges urged producers to "look at their animals as often as possible" to catch any new cases early, per Brownfield Ag News.
The USDA is now adding ground-level sterile fly release chambers directly around the La Pryor site to crash the local wild fly population. A $750 million sterile fly factory under construction at Moore Air Base near Edinburg, Texas, is expected to produce 300 million sterile flies per week by 2027, according to Associated Press. The FDA also issued emergency authorizations for drugs like ivermectin and lotilaner to treat infested animals — a regulatory step not taken in previous decades.
Billions at Stake as State and Federal Officials Clash Over Response
Texas Agriculture Commissioner Sid Miller did not hold back. He blasted the USDA for a "slow, bureaucratic, and incomplete response" and called on the administration to use "all available tools." Texas A&M AgriLife Research estimates a full-scale outbreak could cost the Texas cattle industry between $1.8 billion and $2.1 billion per year. The wildlife and hunting industry could lose up to $9 billion, per Western Ag Network.
Federal officials pushed back on the alarm. The USDA framed the detection as proof its surveillance system is working — they caught live larvae in a single calf before the flies could mature and spread. "This does not threaten the food supply," officials noted, since the parasite attacks living animals, not meat. But the National Cattlemen's Beef Association warned the outbreak still poses a serious threat to producer livelihoods, even if the infested calf survives, according to Associated Press.
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