The unheralded success of a massive operation to control the insidious screwworm offers lessons learned and cautionary tales for mosquitoes and other insect scourges. On a Friday in the fall of 2016, John Welch got an email he’d been dreading—a picture of a mystery insect sent from the Florida Keys. “I knew immediately what it was—and that it was bad,” the United States Department of Agriculture (USDA) entomologist says. He immediately hopped on a plane to Florida. There he found dozens and dozens of endangered Key deer dead or staggering around blind with the tops of their heads or eyes eaten away or terrible wounds on their bodies. “It was horrific,” Welch recalls. Screwworm larvae use sharp mandibles to eat away at the living tissue of their animal hosts. The results can be devastating for livestock and wildlife. But decades-long international control efforts by the USDA and other agencies have helped keep the damaging bugs in check. Image courtesy of ScienceSource/Philippe Psaila. And the clues suggested a threat to far more than just deer. The culprit was screwworm, a fly that lays its eggs in open wounds or in moist areas like eyes and noses of warm-blooded mammals, from dogs to people. When the eggs hatch, the larvae start dining. Without aggressive immediate treatment, “it’s pretty much a death sentence, being eaten alive by the maggots,” says Welch. The stakes were high. In the past, screwworm had devastated the livestock industry all across the US South before the pest was eradicated. Now it was back. Could science win the battle again? The fight had further implications for battles against a host of destructive and disease-carrying insect pests—mosquitoes in particular. Such fights are likely to intensify. In May 2018, the Centers for Disease Control and Prevention reported that between 2004 and …