It took decades of coordinated effort to drive it out. Scientists, ranchers, and federal agencies worked together through the 1950s and 60s to eliminate one of the most destructive livestock parasites ever to reach American soil. By 1966, the screwworm was gone from the United States.
Sixty years later, it’s back.
On a ranch near La Pryor, Texas — a small town sitting roughly 30 miles from the U.S.-Mexico border — a single calf was confirmed infected with screwworm larvae. The USDA immediately issued a quarantine. Federal officials are calling it a national security concern. And across the cattle industry, a quiet alarm is spreading fast.
This isn’t a story that only affects ranchers. It’s a story that could affect every American who buys beef at a grocery store.
What Exactly Is a Screwworm?
The name alone is enough to make most people stop. But the reality is worse than the name suggests.
Screwworms are the larvae of Cochliomyia hominivorax — a parasitic blowfly native to tropical and subtropical regions of the Americas. The female fly lays her eggs in open wounds on warm-blooded animals. When the eggs hatch, the larvae don’t just feed on dead or decaying tissue. They burrow — alive — into healthy living flesh, eating their way deeper as they grow.
Left untreated, a screwworm infestation can kill a full-grown animal within days.
Key facts about screwworms:
- They target any warm-blooded animal — cattle, deer, dogs, and in rare cases, humans
- The larvae spin as they burrow, which is how they got their name
- They are attracted to the smell of wounds, meaning any animal with even a minor cut is vulnerable
- An untreated infestation can expand rapidly as more flies are drawn to the same host
- The risk to humans is considered low, and there are no food safety concerns for beef
“Protecting our livestock industry is a national security issue of the utmost importance.”
— USDA Under-Secretary Dudley Hoskins
The parasite was eradicated from the United States through a method called the Sterile Insect Technique — mass-releasing sterile male flies to disrupt reproduction in wild populations. It was one of the most successful pest eradication programs in American agricultural history. The program was so effective that most people alive today have never heard of screwworms. Until now.
Why the Timing Could Not Be Worse
America’s cattle industry was already under enormous pressure before this confirmation.
The U.S. cattle herd is currently at its lowest level in 75 years. Drought, rising feed costs, and years of herd liquidation have shrunk the national inventory to a point that economists and agricultural analysts had already flagged as a serious supply concern. Beef prices have climbed to record highs. Consumers are already feeling it at the checkout counter.
Now add a flesh-eating parasite to that equation.
If the screwworm were to spread beyond that single confirmed case in Texas, the estimated economic damage to the Texas livestock industry alone could reach $1.8 billion, according to reporting from The Jerusalem Post. That figure doesn’t account for the ripple effects on feed lots, processing facilities, transport, or retail.
The cattle futures markets responded immediately. August feeder cattle futures fell 5.80 cents to 342.625 cents per pound. August live cattle futures declined 1.8 cents. Those numbers translate to real consequences for producers who are already operating on thin margins.
Mexico’s Outbreak Is the Context Nobody Is Talking About
The confirmed Texas case did not emerge in a vacuum.
Since November 2024, Mexico has recorded 27,449 confirmed screwworm cases — with 2,094 currently active at the time of this report. The parasite has been moving northward through Mexico for months. The U.S.-Mexico border spans nearly 2,000 miles, much of it open rangeland where livestock, deer, and wildlife move freely.
Texas Agriculture Commissioner Sid Miller did not mince words in his response to the federal handling of the situation, stating that the “USDA moved too slowly and relied solely on a partial solution that takes years to fully implement.”
That criticism points to a deeper issue: containment at the border relies heavily on the same Sterile Insect Technique that eradicated the pest in the 1960s. The program requires consistent, large-scale releases of sterile flies — a process that takes time to build momentum. Critics argue that the window for early, aggressive intervention may have already narrowed.
For more context on the history of the screwworm eradication program and how it works, the USDA’s Agricultural Research Service has documented the science behind sterile insect programs here.
What Happened the Last Time Screwworms Hit the U.S.
The 1960s Outbreak Left a Lasting Mark
The last major U.S. screwworm outbreak did not resolve itself quickly or cheaply. Wildlife populations were devastated in affected regions. Ranchers suffered millions of dollars in losses. The eradication effort that followed required years of sustained government investment and coordination across multiple states and into Mexico.
That history is exactly why current officials are treating a single confirmed case as a five-alarm situation rather than an isolated incident. The USDA’s Animal and Plant Health Inspection Service maintains current monitoring information on the New World Screwworm threat here.
The lesson from the 1960s was not just that screwworms are destructive — it was that waiting costs far more than acting early.
What Comes Next
As of now, the USDA has confirmed this is the only known active infestation in the United States. A quarantine has been issued for the affected area. Federal and state agencies are coordinating a response.
But the screwworm does not respect quarantine lines on a map. It moves on wings — on the backs of deer, stray dogs, and livestock that cross unfenced land every day. The border region of southwest Texas is not a contained environment.
For American consumers, the immediate impact may not be visible yet. But with a cattle supply already strained to a 75-year low, any meaningful spread of this parasite would accelerate price increases that are already underway.
For the ranchers in the path of this outbreak, the stakes are immediate and personal. One infected animal can become many. Many can become a region. A region can become a crisis.
It happened before. The conditions for it to happen again are already in place. What happens next depends entirely on how quickly — and how seriously — the response moves.
Just act now to eradicate this problem