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An official with Texas A&M AgriLife Extension works at the State Operations Center during Texas’ response to the New World Screwworm in Austin on Friday, June 5, 2026.<\/p>\n
Jay Janner\/Austin American-Statesman<\/p>\n
The New World screwworm was infesting livestock and draining billions from the U.S. economy the last time Texas fought the pest that’s threatening the cattle industry once again.<\/p>\n
Decades before the\u00a0screwworm crossed the U.S.-Mexico border<\/a> and jeopardized Texas ranches this month, it drove a devastating outbreak in the state between the 1930s and 1950s. The infestations\u00a0cost the United States billions of dollars<\/a> and wiped out hundreds of thousands of animals<\/a>.<\/p>\n Federal officials spent millions to eradicate the flesh-eating pest and eventually deemed the effort a success by 1966. Cases continued to surge in following years during the summer months, but after the\u00a0screwworm withdrew to Central America, the U.S. went more than four decades without a single case.<\/p>\n Article continues below this ad<\/p>\n That changed earlier this month, when the U.S. Department of Agriculture said it detected the\u00a0screwworm in a calf in south Texas. Ten more cases\u00a0have since popped up in the state<\/a>.<\/p>\n THE RUNDOWN: Here’s what to know about the flesh-eating screwworm parasite as cases rise in Texas<\/a><\/p>\n Is history repeating itself? What will it take to rid the pest from Texas once again?<\/p>\n Here’s a quick history of the\u00a0screwworm’s time in Texas, from the previous century’s outbreak to the debate surrounding its return.<\/p>\n Article continues below this ad<\/p>\n When did the screwworm last infest\u00a0Texas?<\/p>\n Despite the screwworm’s much deeper roots in the U.S., 1933 was the first year it posed “significant problem” for the country, according to the U.S. Department of Agriculture. A shipment of infested animals carried the pest from the Southwest to the Southeast, and an ensuing outbreak lasted until 1966, when a $32 million eradication program was deemed a success, according to the agency.<\/p>\n What impact did it have on U.S. livestock, pets and humans?<\/p>\n Texas reported 3 million screwworm cases in 1935, according to the Federal Reserve Bank of Dallas. The pest claimed 180,000 cattle head in more than a third of Texas’ counties, the bank reported, citing a 1975 book called “The Peaceful Atom and the Deadly Fly.”<\/p>\n By the 1950s, livestock ranchers were losing around $200 million per year \u2014 equal to about $1.8 billion in 2020 dollars, according to the University of Texas at Austin’s Biodiversity Center.<\/p>\n Article continues below this ad<\/p>\n Texas was part of a region that was considered more susceptible to the pest due to larger livestock populations, more geographic area and better survival conditions through the winter, federal officials said.<\/p>\n How did the U.S. eradicate the pest in the 1960s?<\/p>\n Sterile flies that mated with female screwworms became the vehicle to rid the U.S. of the pest in the 1960s.<\/p>\n An entomologist named Edward Knipling invented a technology that sterilizes male flies with gamma radiation before they mate with females. Female screwworms only mate once, meaning Knipling’s invention \u2014 the Sterile Insect\u00a0Technique \u2014 was set to become\u00a0a population-shrinking tool.<\/p>\n A facility in the south Texas city of Mission was producing up to 150 million sterile flies per\u00a0week by the time the\u00a0screwwom was officially eradicated in 1966, according to the USDA.<\/p>\n Article continues below this ad<\/p>\n Despite those innovations, the screwworm remained in northern Mexico\u00a0and would cross back into Texas every summer in the following years, increasing the U.S. caseload, according to Phillip Kaufman, the head of Texas A&M University entomology department. The last major outbreak in Texas totaled about 90,000 cases in 1972, and before this year, the final case of transmission was recorded in 1982,\u00a0Kaufman said.<\/p>\n How did the screwworm come back?<\/p>\n It’s unclear why or how the screwworm escaped the Dari\u00e9n Gap \u2014 a remote region in southern Panama where its population had\u00a0receded,\u00a0Kaufman said. Little livestock lived there, and the USDA has released 30 or 40 million sterile flies over the region since 2004 as a preventative measure, he added.<\/p>\n “That barrier was an impenetrable jungle,” Kaufman said.<\/p>\n