Click here to download a printable version of this information.

For the past couple of months New World Screwworm (NWS) has been a rising concern for the Southern United States. On September 21, 2025, Mexico’s National Service of Agro-Alimentary Health, Safety, and Quality confirmed the latest case of New World Screwworm in the state of Nuevo León, approximately 70 miles south of the U.S.-Mexico border. In response to the new confirmed case in Mexico, the USDA has implemented a Five-Pronged Plan in an attempt to minimize potential impacts in the United States.

Briefly, the Five-Pronged Plan includes: 1) stop the pest from spreading in Mexico, 2) protect the U.S. border at all costs, 3) maximize our readiness, 4) take the fight to the screwworm, and 5) innovate our way to continued success. Livestock entering the U.S. from the southern border will be monitored closely for signs of infection. The primary goal of the plan and monitoring is to prevent the spread of NWS into the U.S.

New World Screwworm is a species of fly (Cochliomyia hominivorax) that lays eggs in the wounds of living warm-blooded animals. The eggs then hatch within 12-24 hours into larvae that then burrow into the wound to feed. This creates a larger wound that can lead to illness and death if not treated.

The fly was once native to the Southern U.S and was eradicated from the U.S. in 1966 with the targeted release of sterilized male flies. Females of the specie only mate once in their lifetime, so mating with a sterilized male fly resulted in unfertilized eggs. Currently, the U.S. is working with Mexico to mitigate the spread of NWS by developing facilities to disperse sterilized male flies.

In addition to the development of facilities to disperse sterilized male flies, USDA and Mexico officials are monitoring traps along in the Southern U.S. border in Texas, Arizona, and New Mexico. USDA-APHIS also continues to provide education in identifying NWS for the prevention of the potential spread of the flies across the border. As of the previous update by the USDA in late September, no NWS flies have been detected.

Although Montana is a long way from the Southern U.S. border, vigilance is key to prevention of the spread of the flies into the U.S. Livestock are the primary concern for the spread of NWS, pets, people, wildlife, and birds may also carry NWS. The USDA continues to monitor the situation in Mexico for further cases of NWS. More information on NWS can be found on the USDA website.