Congress has found a rare point of unity: stopping U.S. cattle from getting swarmed by flesh-eating flies coming from Mexico. A bipartisan group of lawmakers is pushing forward the STOP Screwworms Act — a bill designed to protect cattle by releasing a peculiar army: sterilized flies.
The goal is to halt the spread of the New World screwworm, a parasitic fly whose larvae feed on the living flesh of livestock, wildlife, and — in rare cases — humans. If left untreated, infestations can be fatal. Now, after years of peace, the pest is back on the radar, crawling north through Mexico and stirring panic among U.S. ranchers and agricultural leaders.
“Combatting the destructive New World screwworm is vital to protecting our cattle, Texas producers, and the American livestock industry as a whole,” said Sen. John Cornyn, who introduced the legislation alongside fellow Texas Republican Ted Cruz, New Mexico Democrat Ben Ray Luján, and a handful of others.
The STOP Screwworms Act would authorize federal funding for a new U.S. Department of Agriculture (USDA) facility to produce and release sterile male flies — a method that successfully eradicated the pest from the U.S. and Mexico in the 1960s and 1990s. The technique works by flooding infested areas with sterile males, preventing wild females from laying viable eggs and collapsing the population over time.
The urgency behind the bill is not just precautionary. The USDA confirmed that screwworms have reappeared in southern Mexico, with infestations spreading as far north as Veracruz and Oaxaca, nearly 700 miles from the Texas border. In response, the USDA temporarily shut down imports of live cattle, bison, and horses through southern border ports last fall after receiving the first case report from Mexican officials in November 2024. Although trade resumed briefly in early 2025 under tight surveillance, it was suspended again amid continued outbreaks.
“Due to the threat of New World Screwworm, I am announcing the suspension of live cattle, horse, & bison imports through U.S. southern border ports of entry effective immediately,” USDA Secretary Brooke Rollins posted on X. “The last time this devastating pest invaded America, it took 30 years for our cattle industry to recover. This cannot happen again.”
Lawmakers behind the bill aren’t just calling it an agriculture issue — they’re calling it a national security one.
“The protection of our animals and the safety of our nation’s food supply is a national security issue of the utmost importance,” Rollins said in a press release, adding that this isn’t about punishing Mexico, but about preventing disaster.
The USDA’s Animal and Plant Health Inspection Service (APHIS) is currently deploying sterile flies via air and ground across southern Mexico and parts of Central America — but lawmakers argue that the effort needs reinforcements.
The bill has already garnered support from several major agricultural organizations, including the American Farm Bureau and Texas Cattle Feeders Association.
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