Just east of the Panama Canal, tucked between patches of rainforest, farmers’ fields, and the Pacora River, there's a green-roofed building that looks like any other factory facility on Earth. Except inside this building, which is jointly operated by the Panamanian and United States governments, they breed flies.

Millions of flies a week. More than a billion a year. Inside, the air smells faintly of rotting meat, as the fly larvae dine on a carefully honed diet of milk, eggs, fiber, and cow blood.

These aren’t your usual houseflies, however. These are highly destructive New World screwworm flies, also known as cattle borers. And to combat them, scientists systematically expose their pupae to radiation in the lab to render them sterile before