A Deadly Parasite’s Return Threatens US Ranchers Too Young to Remember It

On an April afternoon in Fort Worth, Texas, dozens of ranchers wearing tall hats, boots and pressed shirts milled around outside a conference room. The next panel discussion at the annual Cattle Raisers Convention wasn’t slated to start for another 20 minutes, but the cowboys were worried about finding seats. Everyone was anxious to talk about a parasite whose larvae feed on the flesh of living animals. The title of the panel was, “New World Screwworm: The Threat Returns.”

A “flying piranha” that eats its host from the inside out, the screwworm is capable of killing a full-grown steer in just 10 days. It was a relentless, deadly blight on America’s livestock for decades from the 1930s, costing ranchers and the US economy hundreds of millions of dollars each year. Now, after being eradicated from the US since the early 1980s and largely forgotten, top veterinarians expect the screwworm could be back as soon as the summer.