Flesh-Eating Screwworm Returns to Texas After 60 Years

A flesh-eating parasite not seen in Texas since 1966 has returned — and officials are racing to contain it before it spreads through one of America’s most vital livestock regions.

Story Highlights

The U.S. Department of Agriculture confirmed New World screwworm in Zavala County, Texas — the first detection in the state in 60 years.
A second case was subsequently confirmed in another calf in the same county, raising concerns that containment is not yet assured.
Texas Agriculture Commissioner Sid Miller warned that the spread has not been successfully contained, contradicting federal reassurances.
A quarantine zone covering Zavala and Uvalde counties is now in place, with movement restrictions on livestock affecting ranchers across the region.

A Parasite Eradicated Decades Ago Is Back

The U.S. Department of Agriculture’s Animal and Plant Health Inspection Service (APHIS) confirmed on June 3, 2026, that New World screwworm — a parasitic fly whose larvae feed exclusively on the living flesh of warm-blooded animals — was detected in a three-week-old calf in Zavala County, Texas. The larvae were found in the animal’s umbilical area. The pest was previously eradicated from the United States in 1966, making this the first confirmed domestic case in six decades.

New World screwworm is not a food safety threat — the Centers for Disease Control and Prevention confirmed no locally acquired human infestations have been reported, and federal officials stated the parasite does not infest food products. However, the biological danger to livestock is serious. The fly targets open wounds, body orifices, and vulnerable newborns, laying eggs that hatch into larvae capable of killing an animal within days if untreated. For ranchers, that distinction — safe for consumers, potentially devastating for herds — matters enormously.

Second Case Confirmed, Quarantine Declared

Days after the initial announcement, APHIS confirmed a second New World screwworm case in another calf in Zavala County, located approximately 5.6 miles from the first detection. Texas Governor Greg Abbott issued a disaster declaration in response. The Texas Animal Health Commission established a formal quarantine covering Zavala and Uvalde County areas, designating them an official New World Screwworm Infested Zone and imposing livestock movement restrictions on producers in the region.

Texas Agriculture Commissioner Sid Miller issued a pointed warning, stating publicly that “the spread of the New World screwworm has not been successfully contained to date.” That statement directly undercuts the more measured federal messaging and reflects a tension familiar to anyone who has watched agricultural crises unfold — state officials on the ground seeing something different from what federal agencies are reporting from Washington.

Containment Strategy and What Ranchers Face

Federal and state agencies are deploying a multi-pronged response. Animal and Plant Health Inspection Service activated surveillance protocols, sterile fly releases — a proven technique that disrupts reproduction by flooding the population with non-fertile insects — and coordinated inspections across the affected zone. Texas A&M AgriLife Extension is urging producers to check livestock regularly for signs of infestation, including larvae, unusual drainage, or enlargement around wounds and body openings, and to report suspected cases to the Texas Animal Health Commission within 24 hours.

New World screwworm case in Zavala County – bad news for that calf and Texas ranchers. Solid pivot with the headline though.

The banana split saga from earlier still unclear though. What actually kicked this whole thing off?

— Grok (@grok) June 6, 2026

The broader economic stakes are real. Texas cattle ranching is a multi-billion dollar industry, and New World screwworm containment depends almost entirely on speed — fast detection, fast reporting, and fast veterinary intervention. Texas Policy Research noted that the livestock economy faces compounding risk because movement restrictions ripple through supply chains well beyond the immediate outbreak zone. Livestock markets reacted with concern following the initial announcement, reflecting how quickly a localized biosecurity event can generate wider economic anxiety. Ranchers who have already absorbed years of inflation, drought, and input cost pressures are now facing yet another threat outside their control — one that demands immediate vigilance and leaves little margin for error.