The US has fought to keep the New World screwworm, a parasitic fly whose larvae "eat animals alive," out of North America since the 1950s—and has been wildly successful. That success is now in jeopardy. As Sarah Zhang reports for the Atlantic, the USDA's effective process involved raising actual screwworms in factories, sterilizing them with radiation, and dropping as many as 150 million of them a week by plane at-risk areas. The flies were pushed back to Mexico and, finally, the Darién Gap between Panama and Colombia, where in 2006 a sort of aerial border was formed. The land is just 100 miles wide there, and tens of millions of irradiated screwworms continue to descend upon it weekly. But in 2022, that barrier was breached.
The reasons are a little murky but include COVID-related hiccups with cattle inspections and at the one fly factory in Panama that still breeds them, plus a surge in migrant activity. By 2024 the parasite had moved more than 1,600 miles north through eight countries to southern Mexico, prompting US authorities to halt live-cattle imports from that country. Only about 700 miles remain before the screwworm reaches Texas, and our chances of stopping it aren't great.
The Panama facility that produces sterile flies has ramped up output from 20 million to 100 million weekly, but that falls short of what's needed. Texas ranchers and lawmakers are now urging the USDA to build a new fly factory, but that could take years. Drugs to treat screwworm are no longer licensed domestically, and routine branding and tagging practices could expose animals to infection. Per the Atlantic, "Every cut, every scratch, every navel of a newborn calf threatened to turn fatal in the pre-eradication era." (The full story is as fascinating as it is chilling, and explains why that if this comes to pass, already high beef prices could skyrocket.)
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