What is New World screwworm?

New World screwworm (NWS, Cochliomyia hominivorax) is a parasitic fly native to the Western Hemisphere. Female flies lay eggs in open wounds and other body openings of warm-blooded animals. The name "screwworm" refers to the feeding behavior of the larvae (maggots), which burrow—or screw—into living tissue. As the larvae feed, wounds become larger and deeper, attracting additional flies that lay more eggs. If left untreated, infestations can cause severe tissue damage, secondary infections, debilitation, and death.

Although NWS was eradicated from the United States in the 1960s, occasional incursions have occurred. A 1976 outbreak in Texas affected an estimated one million livestock animals and cost producers more than $132 million before it was brought under control. Since 2022, NWS has spread north from Panama through Central America and Mexico. In June 2026, the parasite was confirmed in Texas.

New World screwworm poses a serious threat to livestock, wildlife, pets, and the Texas economy. USDA estimates that a major outbreak could cost Texas cattle producers $732 million and reduce statewide economic activity by $1.8 billion. The threat extends beyond agriculture. NWS can also infest wildlife, particularly white-tailed deer. Texas is home to approximately 5.5 million white-tailed deer, and deer hunting contributes an estimated $9.6 billion annually to the state's economy.

The good news is that New World screwworm is a known enemy, and the tools to combat it already exist. Early detection and rapid reporting are critical to preventing its spread. By staying informed, monitoring animals for suspicious wounds, and reporting suspected cases promptly, Texans can help protect the state's livestock, wildlife, pets, economy, and way of life.