The 'Wall' That Keeps Flesh-Eating Worms Out of America - The Atlantic

The Florida Keys are a place where deer stand next to children at school-bus stops. They lounge on lawns. They eat snacks right out of people’s hands. So when the deer began acting strangely in the summer of 2016, the people of the Keys noticed. Bucks started swinging their heads erratically, as if trying to shake something loose.<br>Then wounds opened on their heads—big, gaping wounds that exposed white slabs of bone. Something was eating the deer alive.

That something, lab tests would later confirm, was the New World screwworm, a parasite supposed to have been eradicated from the United States half a century ago. No one in the Keys had ever seen it. If you had asked an old-time Florida rancher though, he might have told you boyhood stories of similarly disfigured and dying cattle. In those days, screwworms found their way into cattle through any opening in the skin: the belly buttons of newborn calves, scratches from barbed wire, even a tick bite. Then they feasted.<br>Screwworms once killed millions of dollars’ worth of cattle a year in the southern U.S. Their range extended from Florida to California, and they infected any living, warm-blooded animal: not only cattle but deer, squirrels, pets, and even the occasional human. In fact, the screwworm’s scientific name is C. hominivorax or “man eater”—so named after a horrific outbreak among prisoners on Devil’s Island, an infamous 19th-century French penal colony in South America.<br>For untold millennia, screwworms were a grisly fact of life in the Americas. In the 1950s, however, U.S. ranchers began to envision a new status quo. They dared to dream of an entire country free of screwworms. At their urging, the United States Department of Agriculture undertook what would ultimately become an immense, multidecade effort to wipe out the screwworms, first in the U.S. and then in Mexico and Central America—all the way down to the narrow strip of land that is the Isthmus of Panama. The eradication was a resounding success. But the story does not end there. Containing a disease is one thing. Keeping it contained is another thing entirely, as the coronavirus pandemic is now so dramatically demonstrating.<br>Read: The ‘golden death’ bacterium found in a rotten apple<br>To get the screwworms out, the USDA to this day maintains an international screwworm barrier along the Panama-Colombia border. The barrier is an invisible one, and it is kept in place by constant human effort. Every week, planes drop 14.7 million sterilized screwworms over the rainforest that divides the two countries. A screwworm-rearing plant operates 24/7 in Panama. Inspectors cover thousands of square miles by motorcycle, boat, and horseback, searching for stray screwworm infections north of the border. The slightest oversight could undo all the work that came before.<br>The insect is relentless in its search for hosts. Those who fight it must be relentless too.<br>This past August, I went to Panama to meet the people who maintain the screwworm barrier. The Keys outbreak was long over by then, quelled within months by the release of sterile screwworms from Panama. As startling as it was to Floridians, it had been just a small, gruesome blip in the history of the screwworm.<br>A transcontinental screwworm barrier has been in place for 50 years—longer than many of the people who now maintain it have been alive. They work for a joint commission of Panama’s agricultural department and the USDA known as COPEG, or the Comisión Panamá–Estados Unidos para la Erradicación y Prevención del Gusano Barrenador del Ganado. The day before I landed at Tocumen International Airport, two small COPEG planes had taken off and released their precious loads of screwworms over the Panama-Colombia border.<br>More screwworm flights were scheduled for the next day, a Wednesday, and Thursday and Saturday and Monday and so on and on. “We will be here for a long time,” a COPEG staff member in Panama told me with evident pride. “We should be here for the next 100 years.”<br>In the early days of the eradication effort, USDA scientists were not so certain of success—or longevity. They had to bootleg money from other programs because they didn’t have enough funding. In press interviews, they worried about what laughingstocks they’d be if their “idiotic insect-sex scheme” failed and, God forbid, became an extremely mockable symbol of government waste.<br>Read: Decapitated worms get better, see again<br>The man who came up with the scheme, and believed in it most passionately, was Edward F. Knipling, a USDA entomologist who, in the 1930s, spent long hours watching screwworms mate. As a boy, he had waged constant war against insect pests on his family’s Texas farm. “Every plant that we grew,” he later said, “there was some type of insect that was causing damage.” Screwworms infected the farm’s cows and pigs, and Knipling remembered them as one of the worst pests. He had to climb into the hog...