AP – The New World screwworm fly is threatening the $113 billion US cattle industry for the first time in 60 years, with an infestation from its flesh-eating larvae confirmed in South Texas.The USDA said the most recent case was the first in Texas since 1966.The infestation was discovered in a single 3-week-old calf in La Pryor, Texas, about 161 kilometers (100 miles) southwest of San Antonio and 80 kilometers from the US-Mexico border.The deadly flies were detected in Mexico in late 2024, after years of being contained to the southern end of Panama.New World screwworm fly larva (maggot). (USDA)The fly was an annual warm-weather scourge of cattle ranchers from at least the 1930s through the 1960s, until the US eradicated the pest by breeding sterile male flies and dropping swarms of them from planes to mate with wild females.The New World screwworm fly in the Western Hemisphere, and its Old World cousin in Africa and Asia, are unusual among flies because their larvae, or maggots, eat live flesh and fluids instead of dead material.Females lay their eggs in open wounds and mucous membranes after mating only once in their monthslong lives.Any warm-blooded animal, including wildlife, pets and occasionally even humans, can be infested.Livestock are vulnerable, Lee Haines, an associate research professor of biological sciences at the University of Notre Dame, said in an email Thursday.Standard practices with cattle can break the skin, including shearing and de-horning, or even moving them in and out of corrals can cause scrapes and cuts.Birth would also make a mother and calf vulnerable, Haines explained.A New World screwworm fly and egg mass. (USDA)Stephen Diebel, a Texas rancher and president of the Texas & Southwestern Cattle Raisers Association, added that even wounds "as small as a tick bite," can put cattle at risk.Death can result if an infestation is not treated, though a dozen treatments have been approved for use in a variety of species.But agriculture officials were quick to note that the fly does not infest food, and US Agriculture Secretary Brooke Rollins said it's unlikely to damage beef production – welcome news given that consumers are already facing record prices.Federal and state officials and cattle industry leaders have been sounding public alarms about the fly's movement through Mexico and toward the US since a case was confirmed in southern Mexico in November 2024.A map of case detections. (USDA)Officials had considered the pest eradicated from Central and North America nearly two decades before an outbreak in Panama prompted a state of emergency there early in 2023, according to a joint US-Panama program.Cases jumped to Costa Rica and Nicaragua later that year.Edward Burgess, a University of Florida entomologist, said the fly reproduces quickly and is carried across wide areas by its hosts, namely wild animals such as deer."It's hard to stay ahead of it because of how fast that fly is able to move and regenerate," Burgess said.Outside the US, thousands of animals and hundreds of humans sickened.As of June 2, the parasite had sickened more than 171,700 animals and 2,000 people across Central America and Mexico, according to the US Centers for Disease Control and Prevention.There have been 10 human deaths, the CDC says.Starting in May 2025, Rollins closed border crossings for livestock, and on Thursday she credited that move with delaying the fly's arrival in Texas by a year.Haines said climate change is a key element in the spread of a tropical species that thrives in warm weather.Warmer temperatures are expanding the fly's habitat, and cold snaps that killed them off each year in marginal habitats are becoming less frequent and less severe, she said.Texas State Veterinarian Bud Dinges imposed a 20-kilometer quarantine zone covering much of Zavala County, home to La Pryor, and a small part of neighboring Uvalde County.Officials have imposed a quarantine zone to control the spread. (AP Photo/Kevin S. Vineys)Local ranchers are concerned that the fly will spread among wildlife, particularly deer, as a small, short-lived outbreak did in the Florida Keys in 2016.That was the last time a US case was confirmed among animals, though the CDC confirmed a case last year in a Maryland man who had traveled to El Salvador and recovered.The USDA has been dropping sterile flies in South Texas since February, when it opened a center to disperse them there.It is now dropping them twice a week, for a total of 4 million flies, and it's also putting 4 million more a week in the ground as pupae, flies in the stage between larvae and adult.New World screwworm pupae. (COPEG/USDA)With sites outside Panama shut down for years, the USDA invested $21 million in a new fly-breeding facility in southern Mexico, which is expected to begin operations next month.The USDA also is spending $750 million to build a fly factory in southern Texas that can produce up to 300 million sterile flies a week. It is expected to begin operating next fall.Related: 'Devastating' Flesh-Eating Parasite Is Spreading Toward The US, CDC WarnsReleasing sterile flies is both time-tested and highly effective.While males are "promiscuous," in the scientific sense, females are not, and if their one mating hookup is with a sterile male, no eggs from that female will hatch.Once sterile males are prevalent enough, the fly's population declines and then dies out.