Key facts
- Trump administration officials are blaming former President Biden's immigration policies for the spread of New World screwworm.
- The parasitic fly, which decimates livestock, has reappeared in the U.S. after being eradicated in the 1960s.
- Confirmed cases include calves and a goat in Texas, and a dog in New Mexico.
- The U.S. had maintained a barrier using sterile male flies, which was breached in 2022.
- The Trump administration reversed and then re-imposed cattle import bans from Mexico.
- Experts cite illegal cattle imports and issues with sterile fly production as contributing factors.
- Democrats criticize Trump-era funding cuts to USDA programs for disease monitoring.
Trump administration officials are attributing the recent spread of the New World screwworm, a parasitic fly that decimates livestock, to the immigration policies of former President Biden. Agriculture Secretary Brooke Rollins stated that the resurgence of the fly, which had been eradicated in the U.S. since the 1960s, is a direct result of the Biden-Harris administration's "WEAK foreign policy agenda and FAILED immigration policies."
Rollins claimed that the massive movement of people under open borders policies allowed the screwworm to make its way back toward America, reaching Mexico in early 2023 and moving north through Mexico in 2024. The screwworm is a fly larva that consumes living flesh.
Currently, there are five confirmed cases: three calves and a goat in Texas, and a dog from New Mexico. For decades, the U.S. maintained a barrier by releasing sterile male flies in the region south of Central America, aided by the difficult terrain of the Darién Gap. However, the insect began moving north from South America in recent years, overcoming the barrier in 2022 and leading to cases in Panama and Mexico.
Following confirmation of a screwworm case in Mexico in November 2024, the USDA under the Biden administration closed southern ports to live cattle imports. President Trump reversed this decision in February 2025 amid industry protests, but the ports were closed again in May.
Experts like Maxwell Scott, an entomologist at North Carolina State University, suggest that a combination of factors, including increasing pressure on the border and a potential loss of effectiveness in the sterile fly strain, contributed to the breach. Sonja Swiger, an entomologist at Texas A&M University, noted that the rapid spread, with jumps of 50 to 100 miles, indicates animals were moved by truck.
Senator Roger Marshall also blamed immigrants for bringing the screwworm into the U.S. on their pets or themselves. Conversely, Democrats have criticized the Trump administration's actions, including funding cuts to USDA programs for monitoring and responding to screwworm outbreaks, and workforce reductions in agencies like the Animal and Plant Health Inspection Service.
Despite these criticisms, Rollins stated that staffing reductions have not impacted the screwworm mission and that the country has been preparing for the past year. A senior adviser for New World Screwworm Preparedness, John Bellinger, was appointed on Monday. Experts emphasize that eradicating the screwworm again will require significant sterile fly production or new technology, as current production facilities are insufficient.