The USDA says a New World screwworm was found in a calf in south Texas, about 50 miles from the Mexico border. Brooke Rollins said late on Wednesday that it was the first confirmed detection in Texas since 1966.
The finding puts a parasite back inside U.S. livestock territory after it was eradicated from the United States in the 1970s. USDA and Texas officials had been warning livestock owners for more than a year about the parasite’s progression across Mexico.
South Texas calf detection
The calf was in south Texas when the fly was found, and the case is the first in Texas in six decades. Rollins said the animal was infected by the New World screwworm fly, which targets open wounds on cattle and other animals to lay eggs.
When the larvae hatch, they quickly suck on blood and eat the flesh of the host animal. If left untreated, the host animal will die. The parasite can spread quickly where large numbers of cattle and other livestock are kept together, which is why ranchers have been watching the Mexico movement closely for more than a year.
USDA and Texas warnings
In March, Rollins announced a USDA partnership with the army corps of engineers and Mortenson Construction to build a new sterile fly production facility at the Moore airbase in Edinburg, Texas. The plan is meant to bolster production of sterile flies, which mate only once in their months-long lives and produce eggs that do not hatch.
Sid Miller said the screwworm had advanced over 1,100 miles from southern Mexico to Texas. Miller also urged the Trump administration to step up deployment of the screwworm adult suppression system, which uses attractants, bait and targeted insecticides to reduce adult screwworm fly populations before sterile fly releases finish the job.
Rollins and Miller statements
Rollins said Wednesday night, “there is no threat of mass infestation” and “There is no reason to believe this incursion will result in establishment of the pest in our country.” Miller responded, “For months, the screwworm has advanced rapidly through Mexico in spite of the USDA’s existing gameplan” and “Even though billions of sterile flies have been dispersed by USDA, the screwworm has still advanced over 1,100 miles from southern Mexico to Texas, and USDA has missed an important component. Now that it appears the first screwworm has arrived in Texas, the consequences of that decision are now staring us in the face.”
The immediate practical issue for Texas livestock owners is the same one officials have been warning about since the Mexico spread began: the fly finds open wounds, lays eggs, and the larvae feed on living tissue. A Maryland case in August 2025, involving a resident who had traveled to El Salvador and later recovered, showed the parasite can appear outside the livestock setting without transmission, but the Texas case is the first state detection in six decades.
