Screwworm fly detected in Texas decades after cattle threat was largely
eradicated in US
[June 04, 2026]
By JOHN HANNA
The New World screwworm fly has reached south Texas, the U.S. Department
of Agriculture confirmed Wednesday, the first time in decades that the
parasite with flesh-eating larvae has threatened the nation's cattle
industry and only the third time it's appeared in the U.S. in that time.
Agriculture Secretary Brooke Rollins said the case was in a 3-week-old
calf in LaPryor, Texas, about 50 miles (80 kilometers) from the Mexico
border. Texas State Veterinarian Bud Dinges said he has established a
12-mile (20-kilometer) quarantine zone, prohibiting the movement of any
warm-blooded animal — including pets — outside that zone without an
inspection.
Rollins said there have been no other detections of the fly in the U.S.,
and officials were quick to say that while the fly’s larvae are a threat
to livestock production, they don’t infest food. Properly treated, even
the infested calf should recover, Rollins said.
Rollins, U.S. and Texas agriculture officials, and cattle industry
leaders have been sounding public alarms about the fly’s movement across
Mexico for more than a year, spurred on by memories of it causing tens
of millions of dollars of losses — potentially billions in today’s
dollars — before its eradication in the 1970s.
It is the first case confirmed in Texas since 1966, Rollins said.
The months of effort to keep the fly out of the U.S. have included
dropping millions of sterile screwworm flies in the area to mate with
wild females — the same method used successfully before the fly was
eradicated. Rollins said the USDA is confident enough in its
preparations that it believes “there is no threat of mass infestation.”
“There is no reason to believe this incursion will result in
establishment of the pest in our country," Rollins said.
The announcement of the suspected case comes only a day after Rollins
had an online news conference to highlight the nearness of the threat,
with cases been confirmed in Mexico as close as 25 miles (40 km) from
the border — and to outline the USDA's efforts to combat it.
The New World Screwworm fly is a tropical species that decades ago
infested cattle in warm weather across the southern United States, but
it was contained in Panama until late in 2024.
The female fly lays its eggs in open wounds or mucous membranes and they
hatch into larvae that eat flesh — making them unlike most fly species —
and can infest livestock, wild mammals, household pets and even humans.
Infestations can lead to death if left untreated.
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An adult New World screwworm fly sits in this undated photo. (Denise
Bonilla/U.S. Department of Agriculture via AP)
 In August 2025, federal health
officials confirmed a case in a Maryland resident who had traveled
to El Salvador, but the victim recovered and officials found no
transmission of the parasite. Before that, the last outbreak was in
the Florida Keys in September 2016, mostly among wild deer, and it
was contained early the next year without spreading further.
The female flies mate once in their monthslong lives, and if they do
so with a sterile fly, their eggs would not hatch — and the
population would die out over time. Past eradication efforts were so
successful that the U.S. shut down facilities for breeding sterile
flies, leaving only one in Panama for decades.
That is changing. The USDA dedicated $21 million to convert a
fruit-fly breeding facility in southern Mexico into one for breeding
screwworm flies, opened a new center for dispersing sterile flies
bred elsewhere in southern Texas and has started construction on a
$750 million screwworm fly factory there. The breeding facility in
Mexico should be operating next month, Rollins said.
Officials also deployed 8,000 fly traps along the U.S.-Mexico
border, and Rollins said the USDA has tested more than 58,000 fly
samples, along with 19,000 wild animals.
Rollins also closed the U.S.-Mexico border last year to livestock
imports from Mexico, a decision she defended during her news
conference Tuesday. The fly also can travel with people and their
pets and with wild animals, officials noted, but Rollins stressed
Wednesday evening that it doesn't fly great distances on its own.
Dinges said ranchers and pet owners need to understand that it's
important to respect the quarantine zone.
“Please help us prevent any further movement of this pest by staying
put,” he said.
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