An outbreak of New World screwworms, parasitic larvae that feed on the living flesh of warm-blooded animals, has been spreading across Central America since early 2023 and recently reached southern Mexico, raising concerns for the U.S. livestock industry. These larvae cause severe wounds in animals like cattle, horses, and even pets, potentially killing them within weeks if untreated. The U.S. previously eradicated screwworms in the 1960s and 1970s by releasing sterilized male flies from planes to mate with wild females, preventing reproduction and gradually reducing populations. Now, with only one sterilized fly breeding facility in Panama, the U.S. plans to open a new “fly factory” near the Texas-Mexico border to produce hundreds of millions of sterile flies needed to combat the outbreak.

The sterile fly technique involves irradiating male pupae to render them infertile, so when they mate, females lay unfertilized eggs, causing the population to decline over time. The USDA is investing millions to build this new facility and renovate an existing one in Mexico, aiming to protect the multibillion-dollar livestock industry from devastating economic losses. Meanwhile, some southern U.S. livestock trading ports have begun phased reopening due to progress in surveillance and sterile fly dispersal efforts. Ranchers remain vigilant, as no vaccines or repellents exist, and infestations require constant inspection and wound treatment to prevent spread and fatalities.