On June 3, the first case of the New World screwworm (NWS) was discovered in La Pryor, Texas, infecting a three-week-old calf. Since then, screwworm cases have continued to gradually rise. As of July 22, 42 reported cases in cows, sheep, goats, and dogs have expanded throughout New Mexico and Texas – 41 of those reported in the Lone Star State.
NWS are the larvae of the parasitic NWS fly, which burrows and eats the living flesh of warm-blooded animals. Screwworm flies lay eggs in the open wounds of animals, and the eggs hatch into maggots that “screw into” and feed on healthy tissue. Most commonly, the NWS is spread to livestock, pets, and wildlife. Infestations can cause serious and deadly injury to animals if untreated.
Infestations are highly treatable, as long as ranchers and farmers recognize signs early on and treat infested animals with medication. Anyone who notices an animal they suspect to have an NWS infection can report it to the USDA.
The NWS outbreak is not a food safety issue, as NWS burrow only in the living flesh of animals.
The NWS was largely eradicated from the U.S. in 1966, according to the USDA, through intense sterile fly programs. The sterile insect technique (SIT) involves breeding and introducing sterile NWS flies to known populations to slow reproduction and contain the spread. The program was extremely effective in the Sixties, but costly for ranchers and the state agencies that spearheaded it.
NWS returned in 1976 in an isolated outbreak across Texas. SIT once again contained the infestation, but it put significant financial pressure on ranchers and farmers.
According to the USDA’s 2025 NWS report, the cost of an NWS outbreak on the scale of that of 1976 could cost Texas producers $732 million per year until the infestation is eradicated from the area. The estimated loss to the state’s economy is $1.8 billion. The costs show up in lost animals, medications, and labor, as ranchers must be diligent about surveillance and movement restrictions.
Since the outbreak in early June, the Texas Animal Health Commission has placed movement restrictions in 22 Texas counties, meaning that all animals are required to be inspected by the TAHC before moving in and out of the restricted zones. The diligence required to slow the spread can be burdensome for livestock producers.
In the Sixties and Seventies, the U.S. cattle numbers were strong enough to bear the excess strain that NWS caused. Now, herd numbers have reached a 75-year low, according to the Texas Farm Bureau. NWS demands more time and care for herds, and coupled with death loss, ranchers are feeling the pressure. According to the San Antonio Express-News, older, smaller operations may have less ability to absorb the losses, resulting in some ranchers selling their herds.
While NWS primarily affects livestock operations, the flies can burrow in any warm-blooded animal. On June 29, the first infected dog in the state was reported in Pecos County. Though less likely, the USDA recommends pet owners be diligent to look for the signs of infestation if they live in a county where NWS cases have been reported. Most flea and tick medicines are helpful in preventing infestation of NWS larvae by preventing animals from scratching at wounds, which makes them susceptible to infestation.
So far, there have been no reported cases of NWS in Travis County. The closest county with one reported infestation is Gillespie County, about 80 miles away from Downtown Austin.
For more information or to report a case of NWS, go to the USDA’s website, screwworm.gov.
This article appears in July 24 • 2026.