A flesh-eating cattle parasite spreads beyond Texas as new screwworm
cases are found
[June 09, 2026]
By JEFFREY COLLINS
Three more cases of the New World screwworm have been confirmed,
including one outside the main cluster in Texas, demonstrating the
difficulty of stopping a resurgent pest that could devastate the
nation's cattle industry, the U.S. Department of Agriculture announced
Monday.
The screwworm is actually a fly larva that eats living flesh instead of
dead material. The flies lay their eggs in open wounds of animals like
cattle, but wildlife, pets and occasionally even humans can be infested.
The government has a program to breed sterile male flies and drop swarms
of them from planes to mate with wild females, which kept screwworm
contained at the southern end of Panama for decades.
So far, there are five confirmed cases: three calves and a goat in Texas
and a dog from neighboring Lea County, New Mexico. The small dog, which
the USDA initially reported as a Texas case, lives in New Mexico and was
reclassified as the first in that state.
The dog had not traveled to Mexico or Texas, so authorities were
investigating around the property where the pet lived. If they find
infected flies, animal inspections in the area will increase, New Mexico
State Veterinarian Samantha Holeck said during a virtual news conference
Monday.
Screwworm cases continue to climb
The first two screwworm cases were discovered last week in calves a few
miles apart in south Texas. A case was announced Monday in a calf in La
Salle County, southwest of San Antonio, and in a goat in Gillespie
County, west of Austin.
In each case, officials have set up a 12-mile (20-kilometer) quarantine
zone to try to slow the parasite's advance.
Along with cattle and other warm-blooded livestock, scientists worry
screwworms could devastate the millions of wild white-tailed deer in
Texas.
Scientists expect new cases could pop up in the coming days and weeks,
but it doesn't mean screwworm is spreading rapidly, said Edward Burgess,
a University of Florida entomologist who studies the fly.
“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.”
A race to stop the screwworm now moves to Texas
Screwworm gets its name from the maggots’ habit of burrowing — or
screwing — into a wound, according to the USDA. The pest eats the flesh
of the animal, further opening wounds and increasing the risk of deadly
bacterial infections. Animals can die within a few weeks if not treated.
There are a dozen government-approved medications to treat livestock.
The agency and the U.S. cattle industry have been racing to prevent an
outbreak since screwworm was detected in Mexico late in 2024. The USDA
has been dropping sterile flies in south Texas since February and is
working to both increase sterile fly production in plants outside the
U.S. and build a $750 million fly factory in Texas.
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A rancher arrives for a news conference with U.S. Agriculture
Secretary Brooke Rollins at the Knipling-Bushland U.S. Livestock
Insects Research Laboratory in Kerrville, Texas, Monday, June 8,
2026. (AP Photo/Eric Gay)
So far, screwworm's reappearance hasn’t greatly affected beef prices,
which are already near record levels because there are fewer cows in the
United States. Although the parasite attacks live cattle, it does not
infest meat or fruit.
Canada temporarily stopped importing cattle, horses or other livestock
from Texas on Friday. The parasites prefer humid areas where
temperatures are at least 77 F (25 C), making them more of a summer
problem up north.
Fighting screwworms with sterile male flies
Burgess said the long-term solution — breeding sterile male flies — is
months away. Since wild female flies mate just once, if that encounter
is with a sterile male, outbreaks can eventually be halted as the flies
die out.
The goal is to have enough sterile flies to stop the pests from
returning in 2027 after the winter kills off most of them, USDA
Secretary Brooke Rollins said at a news conference at the U.S. Livestock
Insects Research Laboratory in Kerrville, Texas.
Scientists are also working on ways to sterilize only male flies to make
the program even more effective.
Texas officials encouraged ranchers to keep a close eye on their herds
and local wildlife. There's now a 24-hour screwworm hotline and a
website and map for reported cases.
“This is a highly treatable condition if you act on it immediately,”
Republican Gov. Greg Abbott said.
However, Texas Agriculture Commissioner Sid Miller — who lost the recent
Republican primary to a candidate backed by Abbott — said the federal
response will take too long and risks crippling the cattle industry.
Instead, he says a poison bait could eliminate the screwworm problem in
a few months, even if the USDA and other experts say the bait hasn’t
been proven effective and could poison other flies, animals and even
humans.
“What the hell is a good fly?” Miller said in an interview.
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