How the screwworm’s sex life saved steaks

NPR’s Goats and Soda reports that over the past 70 years, the U.S. has been waging a war against a miniature menace: the New World screwworm.

The fly survives by eating warm-blooded flesh: A fly lands on a wound in the skin and lays hundreds of eggs. The eggs hatch into swarms of wormlike larvae, which then burrow into the wound. The larvae have little ridges on their surface, which makes them look like screws inserted into skin. The larvae gorge on the flesh for a few days until they’re full and then fall out of the wound.

screwworm_1-0e3313ab520bc20e0c62493961b88c9b1ae98d53-s1100-c85In the early 20th century, the critters were wreaking havoc on the beef industry. They were costing farmers millions of dollars each year, not just in the U.S. but also in Central and South America. One infection could “kill a fully grown steer in 10 days,” The New York Times wrote in 1977. So in the 1930s, the U.S. Department of Agriculture hired a bunch of scientists to study the fly.

One of them was Edward F. Knipling, a young entomologist who had grown up on a Texas cattle farm. Specifically, Knipling wanted to sterilize a bunch of male flies in the lab and then unleash them into the wild. With enough impotent flies out there courting the ladies, the fly population would eventually plummet, Knipling theorized. Other scientists balked at the idea. They didn’t think it would work.

“Scientists would say, ‘You just can’t castrate enough flies,’ ” says Knipling’s son, Edward B. Knipling. “Telling people you’re going to study the sex life of the screwworm gets some chuckles even today,” the son says. “But in the 1930s, it was such a brand new idea. The scientific community thought my dad was pulling their leg.” But Knipling was dead serious. And for more than two decades, he worked on the fly sterilization project with his colleague Raymond Bushland. They devised a way to grow millions of flies in the lab, using big vats of ground beef, warmed up to body temperature. They figured out how to sterilize the flies using gamma rays — a new technology that came out of research on the atomic bomb. By 1958, Knipling and Bushland had convinced the U.S. government to start air dropping the sterilized male flies across Florida. Each week they unleashed 50 million flies. And what do you know? It worked. Screwworm flies started to disappear. Cattle no longer died from larval intrusion. By early 1959, the screwworm had disappeared from the entire Southeast U.S. “From there, the snowball got rolling,” Edward B. Knipling says. The government started airdropping the flies across Texas, the Southwest and eventually into Mexico and Central America. By 1997, the project had wiped out screwworms all the way from Texas to Panama. Even today the USDA continues to release flies in Panama to prevent fertile males from sneaking out of South America and reinfecting the U.S.

 “It creates a buffer zone,” Edward B. Knipling says. Eradication of the screwworm has saved farmers in North and Central Americas billions of dollars, the USDA says. It has reduced the price of beef. The U.N. called it one of the “greatest achievements in animal health” in the 20th century. This September, Knipling and Bushland will posthumously be given theGolden Goose Award, which honors “seemingly obscure, federally funded research” that has led to big breakthroughs.