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McALLEN — The emergence of the New World screwworm in Texas has raised significant concerns among livestock owners and wildlife experts alike. As this parasitic fly continues to infiltrate local animal populations, questions have arisen regarding its origin and how it made its way to Texas.
Recently, the Texas Animal Health Commission identified a potential source for the infestation: small wildlife and rodents, such as armadillos, opossums, and rabbits. This revelation adds a new layer to the ongoing investigation into how the screwworm breached the Texas-Mexico border.
Prior to this finding, the U.S. Department of Agriculture attributed the screwworm’s arrival to various factors, including border policies under President Joe Biden and the illicit movement of cattle by drug cartels. Lewis R. “Bud” Dinges, executive director of the Texas Animal Health Commission, elaborated on this new perspective during a recent Texas House Committee on Agriculture and Livestock meeting.
Tracing the source
During the committee hearing, Dinges confirmed that epidemiological investigations have not yet linked Texas cases of screwworm to the illegal movement of cattle from Mexico. Meanwhile, the Texas Parks and Wildlife Department continues to investigate the origins and pathways of the infestation.
“That’s very much an unknown, still, at this time. But wildlife is susceptible to New World Screwworm in the same manner that livestock and other warm-blooded animals are,” stated a spokesperson for Texas Parks and Wildlife.
However, it was noted that small mammals typically do not travel long distances, which raises questions about how exactly the screwworm reached Texas, particularly since the first case was detected in LaPryor on June 3.
Moving north
The USDA has previously indicated that models predicted the screwworm’s movement into the U.S. after it began migrating north from South America. This parasitic fly initially moved through Panama, breaking through the Darien Gap, which had historically acted as a barrier.
Following its journey through Costa Rica, the pest rapidly spread through Nicaragua, according to Jeremy Radachowsky, Mesoamerica and Caribbean regional director for the Wildlife Conservation Society. “Not only was it moving very quickly, but it was moving exactly along these paths of cattle trafficking and cattle contraband that we’ve been able to identify earlier,” Radachowsky noted.
Screwworm detections in Central America followed cattle-trafficking routes into Honduras and Guatemala, with Mexican officials reporting their first case in November 2024. Although it was anticipated that the screwworm would arrive in the U.S. by last summer, preventative measures delayed its arrival by a year.
“We’ve been actively and vocally warning that in order to stop screwworm, you have to stop this illegal and unregulated movement of cattle from south to north,” Radachowsky emphasized. However, the exact mechanism by which the screwworm crossed into the U.S. remains unclear.
The USDA closed all southern ports of entry to livestock imports from Mexico in May 2025, a closure that remains in effect. This has successfully prevented the legal movement of cattle from Mexico into the U.S.
Radachowsky pointed out that while there is no clear information on how the screwworm made its way into Texas, it is known that it can infest and travel with other warm-blooded animals, including pets and wildlife. “At the Texas-Mexico border, you’ve got feral pigs, white-tailed deer, and other wildlife, basically moving back and forth as well,” he added.
The unknown
As of Tuesday, there are 13 active cases of New World Screwworm reported in Texas, with an average of 15 suspected cases reported to the Texas Animal Health Commission daily. During the committee hearing, Dinges confirmed that testing for screwworm has been ongoing for over a year, yet no cases had been detected until recently.
State Rep. Ryan Guillen, a Republican from Rio Grande City and committee chair, raised a valid point regarding the likelihood of unreported cases between the Texas-Mexico border and confirmed infestations. Dinges assured the committee that rigorous testing efforts had been in place for an extended period.
“We’ve been submitting anywhere from two to six larvae samples a week since last May and we have not detected any New World Screwworm larvae until June 3,” Dinges stated, reflecting the challenges in tracking this invasive pest.
