A flesh-eating parasitic fly known as the New World screwworm has been detected in a sheep in Coahuila, Mexico, just 31 miles from the U.S. border. The U.S. Department of Agriculture reported the finding, heightening concerns for the American cattle industry and prompting plans for a new Texas fly-breeding facility.
The detection of the New World screwworm in a six-month-old sheep marks the closest the parasite has come to the United States during its recent resurgent migration northward. Federal agriculture data confirms the discovery occurred just 31 miles from the border in Mexico’s Coahuila state, according to reporting by Reuters.
For more than a year, American livestock producers and federal officials have watched anxiously as the pest advanced through Central America and Mexico. The outbreak, which began in 2023, has already generated more than 144,000 cases in animals and over 1,100 in humans across the region, according to agricultural extension data. While the fly is not currently established in the United States, the proximity of this latest case has intensified pressure on the cattle industry, which is already operating with its lowest herd levels in 75 years.
Economic Stakes and Operational Disruption for Producers
The potential arrival of the parasite carries severe financial consequences for livestock operations on both sides of the border. Washington blocked live cattle, horse, and bison imports from Mexico over a year ago in an attempt to keep the pest contained, yet the migration has continued to creep northward.
An outbreak inside the United States could inflict staggering damage on the agricultural sector. USDA estimates indicate that a domestic outbreak would cause $1.8 billion in losses for Texas’ economy alone. Livestock producers in Texas could face losses of $732 million per year, while dairy operations across states like California confront distinct vulnerabilities.
Unlike beef cattle, which can be held back from market during a quarantine, dairy cows produce milk every day that must be processed immediately – if a farm is quarantined or a plant shuts down, milk spoils quickly and has to be dumped,
explained Daniela Bruno, a UCCE dairy advisor for Fresno, Madera, and Kings counties, in an advisory breakdown.
Biology of the Parasite and the Threat to Warm-Blooded Animals
The New World screwworm fly (Cochliomyia hominivorax
) is about the size of a common housefly (or slightly larger), featuring orange eyes, a metallic blue or green body, and three dark stripes down its back. Female flies deposit hundreds of eggs into wounds on any warm-blooded animal, ranging from body openings like the eyes or nose to wounds as small as a tick bite.
“It can affect and kill any warm-blooded animal – any bird, any mammal, including humans,” said Gaby Maier, Cooperative Extension specialist for beef cattle herd health and production at the UC Davis School of Veterinary Medicine. “But we are particularly concerned about our cattle here.”
Gaby Maier, Cooperative Extension specialist for beef cattle herd health and production at the UC Davis School of Veterinary Medicine
Once hatched, the larvae use strong mouth hooks to burrow head-first into living tissue. This feeding process enlarges the wound, invites secondary bacterial infections, and leads to sepsis and death within seven to 14 days if left untreated. Veterinary specialists note that mortality rates in newborn calves can reach 100 percent, and wildlife populations such as deer also remain vulnerable to unmonitored infestation across the border.
Federal Response and Plans for Sterile Fly Production
To combat the advance, the U.S. government has turned to a proven eradication method: releasing sterile male flies into the wild to mate with females, preventing viable offspring. The strategy mirrors the historical campaign that successfully banished the screwworm from the United States in the 1960s.
Agriculture Secretary Brooke Rollins announced that the U.S. will establish a fly-breeding facility at Moore Air Base in Texas, located less than 20 miles from the Mexican border. Funded at $8.5 million, the facility aims to produce sterile insects alongside a potential companion center that could output up to 300 million flies per week.
“The only way to protect the American cattle herd from the devastating threat of New World screwworm is by having a sufficient supply of sterile flies to push this pest away from our border.”
Buck Wehrbein, president of the National Beef Cattlemen’s Association
In addition to the Texas site, the USDA plans to spend $21 million to convert an existing fruit fly facility near Mexico’s southernmost border with Guatemala into a screwworm production center, though that site requires 18 months to become operational. Mexican Agriculture Secretary Julio Berdegué praised the cooperation on social media, expressing hope that coordinated containment efforts will eventually allow cattle trade to resume.
