Flesh-Eating Screwworm Parasite Detected in US Wildlife for First Time in 60 Years

The flesh-eating New World screwworm parasite has spread into United States wildlife populations for the first time in six decades, following its return to domestic cattle earlier this year. The U.S. Department of Agriculture confirmed the detection on Wednesday in a female elk harvested by a hunter on a game ranch in Pecos County, Texas.[1][2][4]

The wildlife infection marks a critical escalation in the ongoing agricultural crisis that began when the pest breached the southern border in June. While livestock can be inspected and treated in controlled environments, wild herds move freely across vast, rugged terrain, complicating federal efforts to track and eradicate the parasite.[3][7]

New World screwworm flies, scientifically known as Cochliomyia hominivorax, lay hundreds of eggs at the edges of open wounds on warm-blooded animals. Within 24 hours, the eggs hatch into larvae that use hook-like mouthparts to burrow into and consume living tissue, effectively eating the host alive.[2][5]

"This detection highlights the critical role hunters, landowners, outdoor enthusiasts and wildlife professionals play in helping detect and manage the spread of NWS," the Texas Parks and Wildlife Department said in a statement following the Pecos County confirmation.[4][8]

Surveillance and containment

Federal and state agricultural authorities immediately expanded their response protocols across West Texas. The Texas Animal Health Commission is modifying a previously established infested zone, while the USDA deploys additional drone surveillance and trail cameras to monitor wild herds in the region.[1][2]

State wildlife officials are urging hunters to inspect their harvests before moving carcasses across county lines. Warning signs of an infestation include visible maggots in wounds, foul-smelling injuries, and abnormal behavior such as isolation, lethargy, or head shaking in living animals.[4][6]

The Pecos County elk is not the only recent detection in the region. The USDA also confirmed a new livestock case this week in cattle in Otero County, New Mexico, bringing the total number of active cases across the two states to seven.[6]

In response to the Otero County detection, the New Mexico Livestock Board and federal officials are maintaining strict movement controls. The simultaneous emergence of cases in both domestic cattle and wild elk underscores the parasite's ability to cross species barriers rapidly.[6][7]

A collapsed biological barrier

The parasite's presence in Texas wildlife is the downstream consequence of a collapsed biological barrier in Central America. For nearly 60 years, a U.S.-funded program released millions of sterile male flies over the Darién Gap in Panama, successfully preventing the South American pest from moving north.[1][2]

That barrier failed in 2023, allowing the screwworm to spread rapidly through Central America and reach southern Mexico by late 2024. The migration forced Washington to temporarily halt all live cattle imports from Mexico, tightening U.S. beef supplies and pushing consumer prices to record highs.[1]

The parasite officially crossed into the United States in June 2026, when veterinarians discovered larvae in the umbilical wound of a three-week-old beef calf in Zavala County, Texas. Since then, dozens of cases have been recorded in domestic animals, including horses and a pet dog in New Mexico.[1]

While the screwworm does not affect food safety and cannot be transmitted by eating beef, it poses a severe threat to animal welfare and production economics. Untreated infestations are frequently fatal, as the expanding wounds attract additional female flies that lay successive generations of eggs.[2][3]

The eradication strategy

To combat the outbreak, the USDA has relied heavily on the targeted release of sterile flies. Because female screwworm flies mate only once in their lifetime, introducing overwhelming numbers of sterile males causes the wild population to collapse over successive generations.[2][7]

The agency recently deployed a newly developed strain of the insect, dubbed NovoFly, which yields exclusively male offspring. This genetic modification doubles the operational supply of sterile flies available for aerial dispersal over infested zones in Texas and New Mexico, supercharging the eradication effort.[7]

The stakes for the U.S. agricultural sector are immense. Before its eradication in 1966, the screwworm cost the American livestock industry hundreds of millions of dollars annually in animal losses, reduced weight gain, and the intense labor required to inspect and treat herds.[1][3]

A widespread outbreak today could cost the Texas economy alone an estimated $1.8 billion in direct losses. Those projections rely primarily on livestock impacts, making the jump into unmanaged wildlife populations a particularly alarming development for agricultural economists.[3][5]

Challenges in the wild

Applying historical eradication methods to wildlife presents entirely new logistical hurdles. While ranchers can physically examine their cattle and apply preventative chemical treatments to shearing or branding wounds, wild elk and deer populations cannot be systematically treated or quarantined.[3][5]

"Early reporting is one of the most important tools we have to protect wildlife, livestock, and pets in the United States," the USDA's Animal and Plant Health Inspection Service noted, emphasizing the reliance on civilian reporting to map the outbreak's true footprint.[7]

The timing of the Pecos County detection coincides with the peak of the Texas hunting season, placing thousands of outdoorsmen in direct proximity to potentially infected herds. Biologists hope this increased human presence in remote areas will function as an ad hoc surveillance network.[4][8]

As the autumn hunting season accelerates, state officials are bracing for potentially higher detection rates. The coming weeks will determine whether the Pecos County elk represents an isolated spillover event or the leading edge of an entrenched wildlife reservoir that could sustain the parasite through the winter.[3][8]