A historic threat to American livestock has reemerged. The New World Screwworm fly, a parasitic insect once eradicated from U.S. soil, has been detected in southern Mexico-roughly 700 miles (1,127 kilometers) from the Texas border. This fly lays its eggs in open wounds of animals, and the resulting larvae feed on living tissue, causing severe pain, infection, and even death. The return of this pest is alarming cattle producers and federal biosecurity agencies.

The U.S. Department of Agriculture (USDA), through the Animal and Plant Health Inspection Service (APHIS), immediately responded by imposing a ban on imports of live animals-cattle, horses, and bison-from affected regions. The U.S. has also ramped up surveillance efforts and reinforced its Sterile Insect Technique (SIT) program operated jointly with Panama. Federal investments in these protective measures already exceed $165 million.

The potential economic impact is enormous. Experts estimate that a full-scale screwworm outbreak could cause over $100 million in annual losses for the U.S. livestock sector, not counting the ripple effects across the supply chain. In Texas, where livestock production is a cornerstone of the rural economy, damages could surpass $1.8 billion, due to both animal deaths and trade disruptions.

A cornerstone of U.S. prevention efforts is the Sterile Insect Technique-a biocontrol strategy in which millions of lab-reared male flies are sterilized and released into the wild. These flies mate with wild females but produce no offspring, steadily reducing the population. This approach, which avoids widespread pesticide use, has been critical to keeping screwworms out of North America for decades. The program releases around 100 million sterile flies per week from a facility in Panama, maintaining a barrier across Central America.

But new challenges have emerged. Climate change is expanding the geographic range of the fly, while migratory wildlife and growing trade flows increase the risk of cross-border transmission. Beyond livestock, screwworms can infest deer, domestic pets, and even humans-raising both public health and animal welfare concerns.

The U.S. government is urging Mexico to bolster its control programs, warning that delays in response could lead to catastrophic consequences. The National Cattlemen's Beef Association and other industry stakeholders are backing the federal measures, stressing that the U.S. took more than 30 years to fully recover from the last major outbreak in the 1960s.

Today's defense against this ancient pest is rooted in precision agriculture, biotechnology, international cooperation, and real-time monitoring systems. Livestock producers are being trained to recognize early signs of infestation, and veterinarians are on high alert across the southern states. Surveillance drones, smart traps, and genomic tools are also part of the evolving toolkit against this high-impact biological threat.

What's at Stake

• Economic Security: Livestock exports are a key part of U.S. rural development and trade agreements. A screwworm outbreak could trigger embargoes and damage market access.

• Food Security: The fly jeopardizes protein supply chains, leading to price hikes in beef and potential disruptions in meat processing.

  

• Public Health: While rare, human infestations have occurred. The parasite invades wounds, causing severe infections and requiring immediate treatment.

• Wildlife Health: Wild deer and other species serve as unintended hosts, making eradication more difficult and expensive.