Every week, planes drop millions of sterilized screwworms over the border of Panama and Colombia, creating a transcontinental “barrier” to the pests far, far away from the U.S.
Here’s one of the planes getting loaded with chilled boxes of adult screwworms:
— Sarah Zhang (@sarahzhang) May 26, 2020
You may have never heard of screwworms, but they are horrible parasites that eat animal flesh. They were once the scourge of livestock, wildlife, and pets alike, and occasionally infected humans. But scientists developed a program 70 years ago to rid North America of screwworms.
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 pens to smear medicine on the wounds of uncooperative sows. “That was a very unpleasant task,” he recalled some eight decades later, in an interview shortly before he died.
Adult screwworms are actually flies, with big red eyes and metallic blue-green bodies. After mating, the females lay their eggs in open wounds, and the resulting larvae eat through a ring of surrounding flesh. Once sufficiently engorged, the larvae drop off the wounds to pupate, emerging as a new generation of flies. As Knipling watched screwworms churn through their life cycle in his government laboratory, he made an observation whose importance he could intuit but not yet put to use: Female screwworms mate only once in their entire life. If a female screwworm mates with a sterile male, she will never have any offspring. So if the environment could somehow be saturated with sterile males, Knipling surmised, screwworms would very quickly mate themselves out of existence.
Raising, feeding, sterilizing, and distributing screwworms by the millions was not easy, but once they figured out how to do it, it was effective. Read about the screwworm eradication program, which continues today, at the Atlantic. The very abbreviated version is at Twitter. -via Metafilter
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