For most in the U.S. beef industry, the New World screwworm (NWS) is a story told by grandfathers, not a modern-day threat. 

Yet with a rapidly shifting risk landscape, livestock producers and policymakers are once again sharpening their focus on this old foe reemerging in southern Mexico.

In May 2025 the USDA suspended imports of live cattle, bison and equines from Mexico into the United States due to the continued and rapid northward spread of NWS. USDA officials have labeled screwworm their “Number 1 priority” in animal health, and cattlemen are taking note.

In June, the USDA announced construction of a sterile fly distribution center at Moore Air Base in Mission, Texas. This move, strongly backed by National Cattlemen’s Beef Association (NCBA) and state affiliates, reflects an urgent need for reliable domestic capacity to serve as a biological barrier along the southern U.S. border.

Although screwworm was officially eradicated from the United States in 1966, maintaining that status has required decades of international cooperation and large-scale sterile fly release programs.

The parasite reappeared in southern Mexico in late 2024. As of June 12, 2025, Mexico reported 2,059 cases, with 258 still active. Now USDA and industry leaders are mobilizing.

During NCBA’s “Economics of Sustainability” session, Ben Weinheimer, CEO of the Texas Cattle Feeders Association, confirmed USDA plans to repurpose an existing fruit fly facility in Mexico to produce an additional 60-100 million sterile flies per week. He also explained the new Mission, Texas, facility, on the site of the old Moore Air Base historically used during the 1960s eradication campaign, will serve as a distribution and aerial release hub should screwworm reappear south of the border.

Impact and efforts

Screwworm females target fresh wounds such as minor cuts, scratches or newborn calves’ navels. The larvae feed on living tissue, causing severe pain, infection and even death. The threat extends beyond cattle to wildlife, pets and humans.

Weinheimer stressed the screwworm undermines producers’ investments in sustainability, genetics and herd management. To combat this, USDA is expanding its use of the sterile insect technique: breeding male flies, sterilizing them via radiation and releasing them to interrupt the screwworm’s reproductive cycle.

Currently, the only active facility producing sterile screwworm flies is in Panama, producing roughly 117 million flies per week. However, experts estimate the United States needs between 300 and 400 million weekly to effectively defend against a border incursion.

To meet this need, the USDA will invest $8.5 million at Mission, Texas, for the distribution center and $21 million in Mexico to convert the fruit fly facility. The Mexico site is expected to be operational by July 2026, and Mission should begin distributing Panama-produced flies by the end of 2025.
Weinheimer cautioned producers against panic-driven projections, emphasizing they should “keep it grounded in science and facts.”

Screwworm may be back in the news, but the U.S. beef industry has the tools, experience and partnerships to keep it under control. With new investments, solid science and strong cross-border cooperation, cattle producers are ready to protect the industry. 

Editor’s note: Elizabeth Rosson is a freelance writer from Louisa, Va.