The Parasite Threatening America’s Cows

This is an edition of The Atlantic Daily, a newsletter that guides you through the biggest stories of the day, helps you discover new ideas, and recommends the best in culture. Sign up for it here.The first thing you should know about the New World screwworm is that it isn’t actually a worm; it’s a fly. At the larva stage, it twists into the flesh of its host, devouring it from within. These wormlike maggots feed on all kinds of warm-blooded animals (the fly’s scientific name is Cochliomyia hominivorax, or “man-eater”), but they pose a serious threat to livestock, and to cattle in particular.The second thing you should know about the New World screwworm is that it’s back. Last week, 60 years after the United States was declared free of the fly, the Department of Agriculture announced that it had found larvae in a three-week-old calf in rural Zavala County, Texas, not far from the Mexican border. Four more infected animals have since been identified across Texas and New Mexico: two calves, a goat, and a dog. The U.S. cattle herd is already the smallest it’s been since 1951 (in part because of drought), and the value of cattle is soaring. As meat-packers pay more for the few animals that remain, they’re passing those costs down the supply chain to beef consumers. To meet the demand, the industry will need to invest in new calves and build up the herd. But the White House’s mixed messages on tariffs has made farmers skittish, and the resurgence of a parasite that eats their animals alive may only make things worse.Since the 1950s, the Department of Agriculture has been warding off the screwworm with a tried-and-true strategy. Workers raise batches of the flies themselves, sterilize them with radiation, and then air-drop them over affected areas each week. Wild flies mate with the sterile ones, slowly eroding the population over time. It’s one of those quietly effective taxpayer-funded programs that’s had an enormous impact in past decades: Before the sterile-insect tec