The U.S. Department of Agriculture confirmed on Monday that New World screwworm has arrived in south Texas, adding two new cases and bringing the total reported to four. One of the new detections was a calf in La Salle County, Texas, while the first case outside the state was found in a dog just across the line in Lea County, New Mexico.
That is the kind of update Texas cattle ranchers were bracing for. The parasite threatens the $113 billion U.S. cattle industry and has already pushed Texas to set up a 12-mile quarantine zone, where animals cannot move out without inspection.
The timing matters because the fly had not been seen in Texas since 1966, after being wiped out in a campaign that once relied on breeding sterile males and dropping them from planes to mate with wild females. For decades, screwworm flies were an annual warm-weather scourge for ranchers, and the reappearance of the pest now has the feel of an old problem forcing its way back into a modern livestock economy.
The return also lands after the flies were detected in Mexico late in 2024, following years of being contained at the southern end of Panama. That earlier spread made the new Texas cases less surprising than they would have been a year ago, but it also left one question hanging over the response: how far beyond these four reported cases the pest has already moved.
For now, the state’s line of defense is the quarantine zone in south Texas, and the pressure is on whether inspections can slow a parasite that lives by burrowing into living flesh. Texas has $17 billion worth of cattle, which means the problem is not confined to one county or one ranch. It is a threat to a market that runs through every level of the state’s livestock business, and Monday’s announcement showed the spread is no longer hypothetical.
