For Immediate Release: September 8, 2025
Contact: R-CALF USA CEO Bill Bullard
Phone: 406-252-2516; r-calfusa@r-calfusa.com
Please find below R-CALF USA’s weekly opinion/commentary that discusses the current state of the screwworm outbreak and provided historical insights regarding the danger the pest poses to the United States. It is in three formats: written, audio and video. Anyone is welcome to use it for broadcasting or reporting.
We Cannot Relax Our Screwworm Defenses
Commentary by Bill Bullard, CEO, R-CALF USA
A media report suggests there’s been a call by the beef industry to reopen the Mexican border to live cattle imports. That report was made about the same time as the Aug. 27 report by Reuters that Mexico had a 53% increase in New World screwworm cases since July. The Reuters report stated there were 5,086 cases of the pest in Mexico, including 649 active cases.
Also around the same time, The Western Producer published another Reuters article titled, “Cattle Smuggling worsens outbreak in Mexico.” That article states that estimates by Mexican authorities and others since 2022 indicate there have been at least 800,000 illegal cattle crossings into Mexico each year from Guatemala, Honduras, Nicaragua and perhaps other countries.
The article implicated organized crime groups as being involved in the illegal cattle trafficking and indicated the cattle enter Mexico with falsified papers and black-market ear tags. Reuters reported that local veterinarians and others in Mexico believe the illegal cattle trafficking was a major factor in the New World screwworm outbreak.
If it weren’t for Reuters’ investigative reporting, who knows when – or even if – we would have learned about the human screwworm case in Maryland, the recent surge in screwworm cases in Mexico, or the likely role that illegal cattle trafficking had on the initial outbreak in Mexico and the continuation of that outbreak.
So let’s take a look at the information provided by our government so we can piece together a clearer picture of the causes of this outbreak and the likelihood that Mexico will contain the pest before it can make its way to the United States.
According to the website for COPEG, the Panama–United States Commission for the Eradication and Prevention of Screwworm Infestation in Livestock, Panama began using the sterile fly technique to maintain a biological screwworm barrier between Panama and Colombia in 2006, and until 2023, the barrier worked.
But the barrier failed in mid-2023, and screwworm outbreaks began occurring in all Central American countries and Mexico, most of which had been free of the screwworm for 20 years. COPEG states that as a result of the pest’s breach of the barrier in Panamanian territory, that barrier was abandoned and moved farther north into Mexico to act as a biological barrier between Mexico and the United States.
A situational map located on the USDA’s website for the period through Aug. 23 reveals that Mexico has now reported 5,542 screwworm cases, 777 of them considered active. So, this USDA information represents increases from what Reuters recently reported–an increase of 456 total cases and 128 active cases within only a matter of days.
From this latest information, we can formulate a rather solid inference about the screwworm situation in Mexico, and that is that the outbreak is still escalating at a rapid pace in Mexico.
But let’s move on. The USDA maintains archived reports from the screwworm infestation in the southeastern and southern states from the late 1950s until the late 1960s. In those archives is a 1958 letter from the USDA to the then secretary-general manager of the Texas and Southwestern Cattle Raisers Association. The letter states that, “Complete elimination of the screw-worm fly in Texas is not possible as long as it exists in Mexico.”
Another document, a 1958 USDA news release, stated: “The flies migrate northward, with the advance of warm weather each year, from southern United States sometimes as far as Virginia in the east and Nebraska in the west. Livestock shipped out of infested areas also spread the pest.”
The archives also contain a 1968 progress report by the Texas Agricultural Extension Service, which included a report from the chair of the Southwest Animal Health Research Foundation, who reportedly stated that until eradication is achieved in Mexico, the barrier zone along the U.S.-Mexico border and the eradicated areas of the Southwestern states will continue to be in danger of screwworm reinfestation.
The USDA archives also state that by “1963, researchers discovered that screwworm flies could fly distances of up to 180 miles. This meant that none of the Southwestern states could be free of screwworms until the pests were eradicated in Mexico.”
Recall on July 9, Agriculture Secretary Brooke Rollins closed the Mexican border for the third time because the screwworm was detected within 370 miles of the U.S. border. Well, that’s only about twice as far as the archived reports said a screwworm fly can travel.
A common theme in the archives is that the New World screwworm fly poses a danger to the U.S. until it is eradicated from Mexico. Both the new and historical evidence support maintaining every possible defense – including keeping the border closed – until that is accomplished.
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R-CALF USA’s weekly opinion/commentary educates and informs both consumers and producers about timely issues important to the U.S. cattle and sheep industries and rural America.
Ranchers Cattlemen Action Legal Fund United Stockgrowers of America (R-CALF USA) is the largest producer-only trade association in the United States. It is a national, nonprofit organization dedicated to ensuring the continued profitability and viability of the U.S. cattle and sheep industries. For more information, visit www.r-calfusa.com or call 406-252-2516.