The New World screwworm — a parasite infamous for eating the flesh of living animals and even humans — is not normally found in the United States. According to the CDC, it remains endemic to parts of South America and the Caribbean. So far, no cases have been detected in U.S. livestock or wildlife.
Back in the 1960s, the U.S. successfully eradicated this dangerous parasite using a groundbreaking strategy: scientists released millions of sterile male screwworm flies into infested regions. When these males mated with wild females, the eggs never hatched, causing the population to collapse. This victory was once considered a triumph of modern science — and a permanent solution.
But now, the parasite is making a troubling comeback. Since 2023, screwworm populations have been steadily increasing in Central America, creeping further north every year. By November 2024, an outbreak in Mexico forced U.S. authorities to suspend livestock imports along the southern border. Although trade briefly resumed in January, it was halted again by May.
The threat is so serious that ports are only reopening in stages, and the U.S. Department of Agriculture has already begun building a new sterile fly dispersal facility in southern Texas to prepare for a potential invasion.
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