What is New World screwworm?

New World screwworm (NWS, Cochliomyia hominivorax) is a parasitic fly native to the Western Hemisphere. It lays eggs in the living tissue of fresh wounds in warm-blooded animals. The name screwworm refers to the feeding behavior exhibited by the larvae (maggots) as they burrow, or screw, into the wound. As the screwworm larvae feed, the wound enlarges, attracting additional female flies, which deposit more and more eggs in the wound. If the infestation remains untreated, the host animal has little chance of surviving the secondary infections that often follow.

The pest was eradicated in the U.S. in the 1960s. Since then, it occasionally reemerges—a 1976 outbreak in Texas affected over a million animals and cost livestock producers more than 132 million dollars—and has resurfaced in Central America and Mexico. NWS began re-emerging above the biological barrier in Panama in 2022 and has continued moving north through Central America and Mexico. In June 2026, screwworm was confirmed in Texas.

NWS poses a serious threat to health and to the Texas economy. According to the USDA, an outbreak could cost Texas cattle producers $732 million and deal a $1.8 billion blow to the state economy. New World screwworm also poses a significant threat to wildlife, particularly whitetail deer. Texas has roughly 5.5 million white-tailed deer and one of the largest hunting economies in North America. Recent estimates place the economic value of Texas deer hunting at approximately $9.6 billion annually.

Texas AgriLife Factsheet

American Farm Bureau

An outbreak could cost Texas cattle producers $732 million and deal a $1.8 billion blow to the state economy, according to the US Department of Agriculture. Texas, with its famous history of cattle drives and cattlemen, still has a bigger herd than any other state, with 12.1 million head — about 14% of total US inventory.An outbreak could cost Texas cattle producers $732 million and deal a $1.8 billion blow to the state economy, according to the US Department of Agriculture. Texas, with its famous history of cattle drives and cattlemen, still has a bigger herd than any other state, with 12.1 million head — about 14% of total US inventory.