Screwworm found 50km from US border in Mexican sheep
Parasite threatens already depleted US cattle supplies
1 June 2026
1 minute read
By: A devastating parasitic fly that eats warm-blooded animals alive and could cause millions of dollars in economic damage to the US economy has been found in a young sheep in Mexico within 31 miles (50 km) of the US border, Reuters reported, citing the US Department of Agriculture on Friday.
The detection heightens the risk for America's beef industry and cattle producers, who have feared for more than a year that the pest would cross into the US and infect livestock after spreading northward in Mexico.
This latest detection of the fly, New World Screwworm, was in a six-month-old sheep in Mexico's Coahuila state, according to USDA data. It was the closest the parasite has come to the US during the most recent outbreak, despite a sprawling effort by USDA and Mexico to contain the pest.
Experts cautioned that if the fly enters the US, it could further spike record beef prices by keeping more calves out of the US cattle supply. An outbreak in the US could cause $1.8 billion in damage to Texas' economy alone, according to a USDA estimate. Texas is the biggest US cattle-producing state.
The US cattle herd is already at its lowest levels in 75 years, and beef prices have set record highs.
The USDA and Mexico's Agriculture Ministry did not immediately respond to requests for comment.
Washington has blocked cattle imports from Mexico for over a year in an effort to keep screwworm south of the border.
Female screwworm flies lay hundreds of eggs in wounds on any warm-blooded animal. Once the eggs hatch, the larvae use their sharp, hooked mouths to burrow through living flesh — feeding, enlarging the wound and eventually killing their host if left untreated.
USDA has invested millions of dollars to set up production facilities that breed sterile flies, the most powerful tool for quelling an outbreak, though the facilities have not yet come online.
