New World Screwworm Cases Confirmed in Texas, Threatening Cattle Industry

The U.S. Department of Agriculture announced Monday that two additional cases of New World screwworm have been confirmed in Texas, located hundreds of miles apart, highlighting the challenge of containing a pest that could severely impact the nation's cattle industry.

The screwworm is a fly larva that feeds on living flesh rather than dead tissue. Female flies lay eggs in open wounds of warm-blooded animals, primarily cattle, but wildlife, pets, and occasionally humans can also be affected.

A long-standing government program that bred sterile male flies and released them from aircraft to mate with wild females had successfully kept screwworm confined to the southern tip of Panama for decades. Now, with four confirmed cases in Texas, including a calf in La Salle County and a dog in Andrews County, officials are on high alert.

The initial cases were discovered last week in two calves near each other in south Texas. Scientists anticipate a few more cases may emerge in the coming days, but this does not necessarily indicate rapid spread, according to Edward Burgess, a University of Florida entomologist.

"When that first case is seen, everyone is being vigilant and their eyes are on it more intensely," Burgess said. "And when you are looking for something, you are more likely to see it." The USDA stated that officials are sampling suspected cases and working to eradicate the pest entirely.

The agency and the U.S. cattle industry have been racing to prevent an infestation since screwworm was detected in Mexico in late 2024.

Screwworm was a seasonal scourge for cattle ranchers before being eliminated in the U.S. in the 1960s.

Its reappearance has not yet significantly affected beef prices, which are already near record highs due to a reduced cattle population. The parasite attacks live cattle but does not infest meat or fruit, and there are a dozen government-approved medications for livestock.

Canada temporarily halted imports of cattle, horses, and other livestock from Texas on Friday. The parasites thrive in humid areas with temperatures above 77°F (25°C), making them more of a summer concern in northern regions.

Burgess noted that the long-term solution—breeding sterile male flies—is months away. Since female flies mate only once, if they encounter a sterile male, outbreaks can eventually be halted as the flies die out.

The USDA is increasing sterile fly production at plants outside the U.S. and building a large fly factory in Texas.

However, Texas Agriculture Commissioner Sid Miller criticized the federal response as too slow, risking harm to the cattle industry. He advocates for a poison bait that could eliminate screwworm in a few months, though it might affect other flies.

"What the hell is a good fly?" Miller said in an interview Monday. The USDA and other experts argue the bait is unproven and could poison other insects, animals, and even humans.

Miller also faulted the USDA for not closing the U.S.-Mexico border to pets as well as livestock. Federal officials noted the infected dog had recently been in Mexico.

"If the larvae fell out all along the ground where that dog went, it's going to spread screwworm all over Andrews County," Miller said. USDA Secretary Brooke Rollins was scheduled to hold a news conference Monday afternoon after being briefed at the U.S.

Livestock Insects Research Laboratory in Kerrville, Texas.