Screwworm Threatens US Livestock as Infected Sheep Found Near Texas Border
A single infected sheep in northern Mexico has escalated fears of a devastating agricultural pest crossing into the United States. On May 29, 2026, the U.S. Department of Agriculture confirmed that a six-month-old sheep in Mexico's Coahuila state tested positive for New World screwworm (NWS)—just 31 miles south of the U.S. border. This marks the closest the parasitic fly has come to American soil during the current outbreak, despite sustained containment efforts by both USDA and Mexican authorities.
The detection has sent shockwaves through the U.S. cattle industry, which is already reeling from historically low herd numbers and record-high beef prices. According to a Reuters report, the USDA estimates that an outbreak in Texas alone could cause $1.8 billion in economic damage. Texas is the nation's largest cattle-producing state, and many producers now fear it is only a matter of time before the fly crosses the Rio Grande.
What Is New World Screwworm?
New World screwworm (Cochliomyia hominivorax) is a flesh-eating fly that infests warm-blooded animals. Female flies lay hundreds of eggs in open wounds. Once hatched, the larvae burrow into living tissue, feeding and enlarging the wound. If left untreated, the infestation can kill the host within days. The pest is not a threat to humans in the same way it threatens livestock, but it can infest pets and wildlife as well.
The Stakes for the U.S. Cattle Industry
The discovery comes at a precarious time for American beef producers. The U.S. cattle herd is at its smallest in 75 years, and beef prices have already reached record highs. An incursion of screwworm could further tighten supply by forcing quarantines, reducing calf crops, and increasing mortality rates among infected animals.
For more than a year, Washington has banned the import of live cattle from Mexico to prevent the pest from entering the U.S. That ban, however, has compounded the shortage of domestic cattle, driving up costs for feedlots and processors. Zane Herrin, division feedlot manager for one of Texas’s largest operations southwest of Amarillo, told Brownfield Ag News that the border closure is hitting feedlots especially hard.
“Another difficult thing with our business model is that we don’t want to stick our neck out to buy expensive calves to stocker,” Herrin said. “We rely on stocker operators to send us cattle, but right now, they’re scared to purchase any because of the market conditions.”
Spread Across Northern Mexico
As of May 25, 2026, the USDA reported nearly 2,000 active NWS cases in Mexico, with dozens of those occurring less than 100 miles from the Texas border. The parasite has been moving northward for more than a year, despite a sprawling binational effort to contain it. Authorities in both countries are currently deploying more than 100,000 sterile male flies per week into active screwworm zones—a number expected to reach 500,000 in the near future.
Texas Ramps Up Defenses
In response to the heightened threat, the Texas Animal Health Commission (TAHC) has added more inspectors along the border. The commission converted vacant positions from other areas into New World screwworm or ectoparasite inspector roles, focusing resources where the need is greatest.
“We took vacant positions that we had in other areas and converted them to New World screwworm or ectoparasite inspector positions,” TAHC Deputy Executive Director T.R. Lansford told KRGV. “We’re just trying to prepare for and be in a better spot to respond because that’s where the greatest need was.”
In addition to increasing personnel, the USDA’s Agricultural Research Service (ARS) recently opened the Knipling-Bushland Livestock Insects Research Laboratory in Kerrville, Texas. The 52,000-square-foot facility is designed to provide the U.S. cattle industry with innovative tools and advanced technologies to manage and eliminate invasive fly and tick pests. The lab will also pursue the eradication of ticks and blood-feeding flies that harm and kill cattle.
Sterile Insect Technique: The First Line of Defense
The most powerful tool for quelling an outbreak is the sterile insect technique (SIT), which involves releasing large numbers of sterilized male flies into the wild. These sterile males mate with females, producing no offspring and eventually collapsing the population. A new sterile fly distribution facility in south Texas is already operational, allowing sterile flies from Panama to be distributed to the Texas border. A Mexican facility is expected to begin producing sterile flies in July 2026.
National Cattlemen’s Beef Association CEO Colin Woodall expressed confidence in the industry's preparedness. “We’re ready. We’ve had over a year and a half to look at this, to watch it, to develop new tools, to get new approval for emergency-use products,” Woodall told Brownfield Ag News. He also noted that the EPA and FDA have approved products to help manage the pest.
Broader Implications and What This Changes
The emergence of screwworm so close to the U.S. border represents a turning point in the battle against the parasite. While the pest has not yet been confirmed on American soil, experts warn that containment in Mexico is becoming increasingly difficult. The discovery in Coahuila—just 31 miles from the border—suggests that the fly is moving faster than anticipated.
Economic Fallout and Market Disruption
If the screwworm crosses into the United States, the economic impact could be severe. The USDA estimates that an outbreak in Texas alone could cost $1.8 billion. More broadly, the disruption to livestock markets could spike already high meat prices, affecting consumers nationwide. The ban on Mexican cattle imports has already contributed to a shortage of domestic cattle, and an outbreak would likely exacerbate that shortage.
For comparison, a similar scenario played out in the Falkland Islands, where a major traceability breach led to the culling of 271 head of cattle. While the circumstances differ, the logistical and economic challenges of managing an invasive pest are a stark reminder of how quickly a disease or parasite can upend a regional livestock economy. Read more about the Falkland Estate situation here.
Long-Term Solutions and Research
The opening of the Knipling-Bushland lab is a sign that the USDA is investing in long-term solutions. The facility will focus on developing new tools to combat not only screwworm but also ticks and other biting flies that threaten livestock. However, critics note that the lab's debut comes as the outbreak is already at the border, and some question whether research can keep pace with the immediate threat.
Texas cattle producers like Zane Herrin are cautiously optimistic. “Texas producers are surprised we haven’t had it in Texas yet,” Herrin said. “I think it’s going to get pretty close, but from our perspective, we’re far enough north that it will reach our other operations further south before it gets to us and we’ll be able to respond.”
But not everyone shares that confidence. Stateline’s Kevin Hardy reported that southern states are bracing for a potential invasion that could disrupt livestock markets and raise already high meat prices. The federal government has banned live cattle imports from Mexico, compounding the shortage of domestic cattle.
Preparedness and Next Steps
For now, the USDA and Texas authorities are focusing on surveillance, quarantine, and the continued release of sterile flies. The Texas Animal Health Commission says it will continue to evaluate whether more inspectors are needed, particularly in the Rio Grande Valley. If necessary, the commission will ask state lawmakers in Austin to open up additional positions.
Industry groups are also pushing for more resources. The National Cattlemen’s Beef Association has called for increased funding for sterile fly production and emergency-use product approvals. Woodall said he is encouraged by the progress so far but acknowledged that the situation remains fluid.
“We have the sterile insect technology facility in south Texas that is under construction,” Woodall said. “We have the new distribution facility that is already up and running and is allowing those sterile flies out of Panama to be distributed to the Texas border.”
The coming weeks will be critical. If the screwworm crosses into Texas, the response will be tested in real time. If it is kept at bay, the current measures may serve as a blueprint for future pest management. Either way, the detection 31 miles from the border has made one thing clear: the threat is no longer hypothetical.
Conclusion
The discovery of the New World screwworm just 31 miles from the U.S. border is a wake-up call for the American cattle industry. With nearly 2,000 active cases in Mexico, dozens within 100 miles of Texas, and the U.S. cattle herd at historic lows, the stakes could not be higher. Federal and state agencies are scrambling to bolster defenses, but the pest is moving northward faster than containment efforts can keep up.
The sterile insect technique remains the most promising tool, but production facilities are still ramping up. In the meantime, Texas cattle producers are on edge, watching the border and hoping that the fly does not make the final leap. The next few months will determine whether the U.S. can keep a devastating parasite at bay—or whether a new agricultural crisis is about to unfold.
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