The Return of the Screwworm: A 60-Year Nightmare for US Agriculture

The discovery of the New World screwworm in a calf in Texas marks a historic breach in US biosecurity, reviving a pest eradicated in 1966 and threatening the nation's livestock economy. The parasite, known for burrowing into living tissue, is believed to have crossed from Central America into Mexico before evading containment barriers to infect the animal near the US border.

The Biological Threat and Texas Discovery

The New World screwworm (Cochliomyia hominivorax) is a parasitic fly whose larvae feed on the living flesh of warm-blooded animals. Female flies lay eggs in open wounds or navel cords, which hatch into hundreds of larvae that can kill an animal if untreated.

The recent case involves a three-week-old calf in LaPryor, Texas, which is believed to have contracted the larvae from its mother, evading the biological barriers that kept the pest contained for decades. This is the first confirmed animal case in the US since eradication efforts were successful in the mid-20th century.

Economic Forecasts and Rising Case Numbers

The economic implications of this outbreak are severe. Between mid-July and mid-August 2025, Mexico reported a 53 percent rise in screwworm cases, indicating a rapid spread through the region. Experts warn that an outbreak in the US could cost the Texas economy up to $1.8bn in losses.

Human Risk: While rare, humans can be infected, particularly vulnerable groups like the homeless who lack access to hygiene and medical care.
Treatment Cost: Modern ranchers lack the experience to diagnose and treat the pest, making manual larval removal and insecticides a costly and labor-intensive process.

Supply Chain Disruptions and Beef Prices

The discovery has triggered immediate supply chain responses. The US has halted cattle imports from Mexico, a move that has already tightened the supply of beef cattle. With US cattle herds at a multi-decade low due to severe drought and high feed costs, the import suspension has pushed record-high beef prices even higher.

Mexican cattle are typically imported to the US for fattening before slaughter. A diminished slaughter rate and the inability to import live cattle will likely result in further shortages and price increases for American consumers.

The Strategy for Eradication and Future Risks

Authorities have established a quarantine zone around the affected farm and are implementing a program of sterile male release—the same method used successfully in the 1960s. However, experts point to potential disruptions during the COVID-19 pandemic and increased cross-border movement as factors that allowed the fly to re-establish itself.

The future outlook remains precarious. Without strict vigilance and the rapid deployment of sterile flies, the US could face a widespread infestation that endangers not only livestock but also household pets and wildlife.