Screwworm Case in Texas Horse Puts Nature Coast Livestock Owners on Notice

What was confirmed

On Sept. 9, veterinarians confirmed the first New World screwworm infestation in a U.S. horse since the pest was eradicated from the country in the 1960s. The case turned up in a working ranch horse in Presidio County, Texas, with larvae found on the animal’s hind limb. It is the first equine case identified during the current outbreak, which has been moving north through Mexico after breaking through a decades-old containment line near the Darien Gap in Central America. No case has been detected in Florida.

New World screwworm is the larval stage of a blow fly whose females lay eggs in open wounds on living animals, not on carcasses, which distinguishes it from more common maggot infestations. The larvae feed on healthy tissue, according to University of Florida veterinarian Sally DeNotta, and can cause severe secondary infection or death if untreated, per UF entomologist Edwin Burgess.

Why it reaches this coast

Florida has no confirmed screwworm activity, but UF veterinarians say that’s a matter of geography and time, not immunity. DeNotta said the state’s year-round warm climate can sustain the parasite’s life cycle, and current spread forecasts suggest it could move through much of the Southern United States. Florida’s horse industry, anchored by the Ocala-Marion County region, officially designated the “Horse Capital of the World” by the Florida Department of Agriculture and Consumer Services, covers more than 70,000 acres devoted to horse-related use statewide.

That statewide exposure matters for the Nature Coast and Levy County, where cattle operations and horse farms sit outside the Ocala hub but rely on the same open pastureland, fencing and animal-movement patterns that Burgess identified as the primary way screwworm spreads. Any cut, scrape or wound on livestock, from wire, brush or routine handling, becomes a potential entry point if the fly reaches the region.

State and university response

FDACS has assembled a task force focused on surveillance, insecticide stockpiling, identification training for veterinarians and preparation for sterile-fly releases should the pest cross into Florida, Burgess said. The control method that eliminated screwworm from the U.S. decades ago, releasing irradiated male flies to mate without producing offspring, known as the Sterile Insect Technique, remains the primary tool being scaled up now. A USDA facility in Texas is being converted to produce sterile flies, with production expected to start in early 2027. DeNotta said the country will need far more sterile flies than currently available to control the parasite across its potential U.S. range.

What owners are doing now

At Mill Creek Farm, a 335-acre nonprofit horse retirement facility, staff have stepped up checks of fence lines for nails and splinters that could cause wounds, and the farm quarantines incoming horses for 30 to 60 days. Beauty’s Haven Farm and Equine Rescue, currently not accepting new horses, maintains fly traps, daily manure removal and fly masks for its animals as routine precautions.

UF veterinarians are urging owners statewide, including in North Central Florida and along the Nature Coast, to inspect animals regularly for wounds, avoid standing water and spoiled hay that attract flies, and report suspicious wounds to a veterinarian rather than assume the worst. “We want Floridians to be informed and ready, and level-headed about it, as opposed to reactionary and dramatic,” DeNotta said.

What to watch

There is no confirmed case in Florida, and no state or federal comment period is currently open on new screwworm rules. The next concrete marker is the USDA’s Texas sterile-fly facility, expected to begin production in early 2027, a step officials say is necessary before any large-scale containment effort could reach the Southeastern U.S. if the parasite continues its northward spread.