The New World screwworm (NWS, Cochliomyia hominivorax) is a devastating parasitic fly native to the Western Hemisphere. When NWS fly larvae (maggots) burrow into the flesh of a living warm-blooded animal, it lays eggs in the living tissue of fresh wounds. The larvae (maggots) feed on the host’s flesh, causing severe wounds and often death if untreated. NWS can infest livestock, pets, wildlife, occasionally birds, and in rare cases, people.

The pest was eradicated in the U.S. in the 1960s. Since then, it occasionally reemerges and has resurfaced in Central America and Mexico. They are controlled only through the release of sterile males, known as the sterile insect technique (SIT). This approach, along with regular active surveillance and livestock inspections, has proven highly successful.

As of May 2025, renewed attention to this parasite is crucial, as it may pose future risks to livestock and wildlife. This is a fast-moving issue, as we have seen the border close, then open, now closed again. With a reported case in Veracruz in Mexico, the screwworm is 370 miles south of the U.S./Mexico border (see map below). It will be very important for us in Arizona to track these developments.

Secretary of Agriculture Brooke Rollins has been transparent in the plans the Department has created to fight this pestilence. They are focusing on three strategies to strengthen our response:

1. Effective controls on the movement of animals
2. Strong surveillance systems and public outreach
3. The use of sterile insect technology and exploring additional innovative methods of eradication. 

Click this link to read and/or download the Domestic Readiness and Response Policy Initiative 5-Prong Strategy from USDA. This site will be updated as new information is available.