The U.S. Department of Agriculture’s Animal and Plant Health Inspection Service has confirmed the presence of New World screwworm larvae in a young calf, located less than 80 miles from the Texas-Mexico border. These harmful maggots were found in the umbilical area of a three-week-old calf in Zavala County, Texas.
Concerns over the reemergence of the New World screwworm have been lingering among Texas officials. The recent findings in Zavala County threaten livestock producers in Texas and beyond if the infestation spreads. State authorities are on alert as the pest migrates north from Mexico toward Texas, according to local reports.
During a Republican dinner in February, Texas Agriculture Commissioner Sid Miller made a stark warning to ranchers, hunters, and pet owners about the increased activity of the parasite this season. He remarked, “Active screwworm flies have been spotted just 297 miles south of the Rio Grande, and it’s winter. This shouldn’t be happening right now.” He also mentioned that a mild winter could mean trouble as spring approaches.
Miller expressed that the situation is serious, stating, “Everyone will be impacted in some way—livestock, pets, and even humans. Ranchers, deer hunters, and pet owners need to be vigilant.”
In August 2025, Texas Governor Greg Abbott declared a state-wide disaster, preparing for the worst if the screwworm crossed the border. This parasite hasn’t been seen in the U.S. since its eradication in 1966.
In a recent press release, the USDA issued a warning about the New World screwworm’s threat to various animals and mentioned that the larvae can cause severe harm, leading to significant economic losses for farmers.
U.S. authorities have been anticipating the arrival of such pests from Mexico and are executing plans to address them. Dudley Hoskins from the USDA emphasized that protecting livestock is crucial, and the agency is ready to act, having invested resources to eliminate the pests as they’ve reappeared in Central America and Mexico.
The USDA is implementing strategies that include establishing infection zones, controlling movement, and enhancing surveillance. Additionally, they plan to release sterile screwworms to further fight the infestation.
Experts hope to replicate the successful eradication methods used in 1966. The Sterile Insect Technique has been shown to be effective, although it won’t yield immediate results.
Monitoring herds closely is vital to prevent the spread of these pests. The movement of infected animals is primarily responsible for their geographical spread.
The potential economic impact on Texas cattle producers and the hunting industry from this infestation could exceed $2.1 billion, according to Texas A&M AgriLife.
Newborn livestock are particularly vulnerable to screwworms, as tiny wounds—such as those from routine medical procedures—can attract the invasive larvae.
While generally rare, the New World screwworms can affect humans as well. As of June 2, 2026, reports indicated 171,700 infected animals in Central America and Mexico, alongside only two thousand human cases, as per the CDC.
Since these parasites reappeared, only one human infection has been confirmed in the U.S., linked to travel from El Salvador in 2025.
