This time a year ago, experts were already predicting the return of the carnivorous screwdriver in the United States: that’s not the case if but whenWayne Cockrell, a Texas rancher, mourned for me at the time. The worms had been eradicated from the United States to Panama and then encircled through be released regularly about 20 million worms every week on the narrow Isthmus of Panama. But the worms, which develop into flies as adults, had jumped the ropes and infested much of Mexico by last year. This month, they arrived in Texas.
The math of the crisis then and now is pretty simple: The US Department of Agriculture’s screwball program can’t produce enough sterile adults to control the parasite. The Panama factory has already increased its weekly production to a maximum of only 100 million, but more flies, many more are needed to stop the caterpillars again: 500 million.
Two new factories are under construction, but both have been delayed. according to information in Politicsdue to the Trump administration’s strict review of government spending last year. The first, in Mexico, will be fully online only this season and the second, the largest in Texas, in 2028 season. “To win this war, it’s all about the number of sterile flies,” Cockrell, who is also the second vice president of the Texas and Southwest Cattlemen’s Association, emphasized to me recently.
At the same time, the worms will continue to spread throughout the country, and farmers will continue to suffer serious injuries in their livestock. The best thing farmers can do until more disease-free flies arrive is to “hold the line, weather the storm,” Jason Sawyer, chief science officer of the East Foundation, an agricultural research organization that manages six farms in Texas, told me. Optimistically, he expects it to take three years to eradicate the caterpillars in the United States. In fact, he thinks it will take five years.
That parasite is the biggest threat to cattle—which it can push beef prices higher—but they can also infect pets, wildlife, and even the unlucky human. After the first case of worms was discovered in a Texas calf stump on June 3, 15 more animal cases quickly became known. The cases are scattered over hundreds of square miles, an alarming geographic spread that suggests worms have spread across the United States in more than a single outbreak. Experts told me they hope and expect the distemper won’t spread far outside of Texas, but one case, in a dog, had already been found near the state border in New Mexico.
Waiting for more flies is more frustrating because the technology itself is so old. It has remained essentially unchanged since the worms were first eradicated in Texas, in the 1960s. The worms are raised in a factory and then blasted as pupae with radiation to render them incapacitated. When released en masse as flies, sterile males mate with wild females to produce inviolable eggs. Over the years, the screwdriver program improved this technique but saw no reason to make major adjustments. Why mess with something that isn’t broken?
In 2026, the outlook is completely different. The search is on for anything and everything that can reduce the long wait for more helpless flies. The USDA announced last week 105 million dollars in funding 40 projects that run the gamut, including new irrigation techniques and detection dogs and new pesticides.
The USDA has even revived a genetically modified screwdriver made exclusively for men. almost a decade before. Factory-raised males and females are currently released together, but only sterile males are suitable for eradication. (They mate often, while female woodpeckers only mate once.) To that end, Maxwell Scott, an entomologist at North Carolina State University, began working on the male-only problem for the USDA in 2010. The lab science went quickly, he told me, but getting approval for field trials in Panama took three years. His team then created a better version, which was never tested. The all-male project was more or less put on hold, much to Scott’s disappointment. “It was a lot of work to make these models, and I thought they were great,” he said recently. “It wasn’t my decision.” He stopped working on screwworms.
Last year, as the screwdriver was about to return, Scott heard that the USDA was interested in the newest version of the male-only variety again. The agency in March filed paperwork to register the best-of-breed offeringRenamed “NovoFly”– as medicine and the Environmental Protection Agency. (The USDA did not respond to my questions about when NovoFly will be ready for use.) Scientists are still waiting for approval for a field trial in Panama, though. If the male-only strain is proven to work soon and deployed quickly, switching to it could reduce the shortage of sterile flies. Scott also received a grant to continue working on the male-only problem as part of a USDA funding push.
Ironically, the technology behind these male-only models is now outdated, Scott said. Since the introduction of this early strain, CRISPR has revolutionized the ability of scientists to manipulate DNA in the laboratory. Scott is now interested using CRISPR to create a “gene driver” which forces sterility to spread among the wild screwdriver. Theoretically, a release one of flies carrying the gene can even, over time, destroy the caterpillar population. At that time, worms could be eradicated not only from North and Central America but also from South America, making the screwdriver barrier in Panama completely obsolete. But he gives the gene is controversial especially because they can be uncontrollable once out in the wild; The technology in the screwdriver is not ready for field testing.
For now, Texas ranchers waiting for more fruit flies must rely on old-school strategies dating back to the eradication era: checking cattle, treating wounds with anthelmintics, and restricting the movement of infested animals. “When everyone in the area is doing it, you can put a small number in the environment. But all it takes is one neighbor, like a source, isn’t it,” Cockrell says. And the work is labor intensive, because cattle herds can spread over hundreds or even thousands of acres, and ranches often employ fewer workers than they used to. “I’ve had people ask, ‘My parents told me about how they had to manage this in the ’60s,'” Sawyer recounted. “‘I don’t know if I can do it.'”
Even if farms take good care of their own livestock, wildlife can serve as a permanent breeding ground for the snails. The role of wildlife in today’s outbreak is a “wild card,” Sawyer said. The deer population especially increased following the eradication of the caterpillars. (It’s directly related: Worms used to kill 40 to 80 percent of fawns in Texas every year.) “There really aren’t any good answers” to dealing with fawns in wildlife, he told me. How much wildlife will contribute to the outbreak will become clearer in just a few years—when eradication efforts are expected to have enough flies to push the caterpillars back to the Mexican border, and eventually to the Panamanian border.
