The agricultural community in South Texas is on high alert following the confirmation of the first case of New World screwworm in the United States. This parasitic fly, known for its devastating impact on livestock, was detected in a three-week-old calf in La Pryor, Zavala County. The confirmation came from the U.S. Department of Agriculture (USDA) after testing a sample at their National Veterinary Services Laboratories in Ames, Iowa.
The discovery has sparked immediate action from state and federal authorities, who have been preparing for the potential arrival of this pest for months. The screwworm, which targets the live flesh of warm-blooded animals, poses a significant threat to the state’s $15 billion cattle industry and other livestock.
The Nature of the Threat
The New World screwworm is a parasitic fly that lays its eggs in open wounds of warm-blooded animals, including cattle, pets, wildlife, and even humans. The larvae feed on the flesh, causing severe injuries and often leading to death if untreated. Secretary Brooke Rollins emphasized the importance of vigilance, urging residents to check their pets for signs of infection, such as infected wounds and the presence of screwworm eggs or larvae.
Despite the alarming nature of the discovery, officials assured the public that the food supply chain would not be affected, as screwworms do not infest meat, fruits, or vegetables. The last outbreak of screwworm in the U.S. was eradicated in the 1960s, with the pest subsequently contained in Central America. However, recent cases in Panama, Costa Rica, Nicaragua, Honduras, and Mexico have raised concerns about its resurgence.
Preventive Measures and Response
Since early 2026, the U.S. has deployed over 8,000 traps capable of detecting screwworm, resulting in the testing of 58,000 samples and 19,000 wildlife specimens. All tests had been negative until the recent confirmation. In response to the threat, the USDA shut down the southern border to live animal imports in May 2026, limiting the supply of cattle in Texas.
Officials are employing the sterile fly method to combat the infestation. This involves producing male sterile flies that reproduce unviable eggs with female flies, who can only reproduce once in their lifetime. The USDA, in collaboration with officials in Mexico and Panama, has established sterile fly production facilities in Metapa, Mexico, and is building another in Edinburg, Texas, set to open in fall 2027. Additionally, two fly dispersal facilities have been launched in Tampico, Mexico, and Edinburg.
Political and Public Reactions
The confirmation of the screwworm case has sparked a range of reactions from political figures and the public. State Representative Don McLaughlin initially claimed the fly was just one mile away from the U.S.-Mexico border, a claim that Secretary Rollins debunked, calling McLaughlin well-intentioned but incorrect. McLaughlin later tweeted, “Well … maybe we should listen to our state representatives,” and pledged to work with local, state, and federal agencies to combat the threat.
Texas Agriculture Commissioner Sid Miller criticized the federal government’s response as slow, bureaucratic, and incomplete. He urged President Donald Trump to approve the deployment of the Screwworm Adult Suppression System (SWASS), a method tested in the late 1970s to eradicate screwworms using bait and insecticides. Miller expressed frustration with the current response, stating, “We have the ability to shut that and eradicate that screwworm. We can do it in about 60 days.”
Historical Context and Future Steps
The last significant outbreak of screwworm in the U.S. was eradicated in the 1960s, with the pest subsequently contained in Central America. However, recent cases in Panama, Costa Rica, Nicaragua, Honduras, and Mexico have raised concerns about its resurgence. In February, Florida officials detected screwworm larvae in an imported horse from Argentina, but the case was contained within a quarantine area.
As officials work to contain and eradicate the screwworm infestation, the agricultural community in South Texas remains vigilant. The coordinated efforts of state and federal agencies, along with the support of local communities, will be crucial in mitigating the impact of this parasitic threat.
