U.S. and Mexico Join Forces to Eradicate the Flesh-Eating Screwworm with Sterile Flies

The resurgence of the New World screwworm (Cochliomyia hominivorax), a flesh-eating parasite that severely affects livestock, has prompted a joint response from the United States and Mexico. In early June 2025, the U.S. Department of Agriculture (USDA) announced a strategic plan involving a total investment of $21 million to modernize the sterile fly plant in Metapa de Domínguez, Chiapas. The facility will now produce between 60 and 100 million flies per week, tripling previous emissions from Panama and enabling a total weekly output of up to 160 million [citation: El País, AP, Reuters].

The initiative is complemented by a parallel project in Texas, where $8.5 million will be invested to build a new sterile fly production center at Moore Air Base, near the Mexican border. This would be the first facility of its kind in the U.S. since the 1960s and aims to breed up to 300 million flies weekly, which, combined with production in Mexico and Panama, will be used to overwhelm wild populations [citation: Reuters, El País].

This biological control method, known globally as the Sterile Insect Technique (SIT), was instrumental in eradicating screwworms from U.S. territory in the 1960s. Since female flies only mate once, mass-releasing sterile males prevents reproduction [citation: USDA, El País]. The strategy proved successful across Central America and Mexico during the 1970s and 1980s, largely supported by the Panama-based production plant [citation: Science Direct].

The current outbreak has been detected in southern Mexico, prompting the U.S. to suspend cattle imports since May 11, 2025. Mexican authorities report a 51.8% drop in cases since April and have launched emergency drills across six southern states to maintain surveillance [citation: Reuters, El País].

The joint plan prioritizes five key strategies: stopping the parasite's spread in Mexico, protecting the U.S. border, strengthening surveillance, ensuring rapid response capabilities, and mass-releasing sterile flies—through binational cooperation [citation: USDA, AP].

Why Is This Plague So Dangerous?

The screwworm infests open wounds, and its larvae consume live tissue, causing severe infections, massive economic losses in cattle industries, and risks to wildlife, pets, and even humans [citation: USDA]. A 2016–2017 outbreak in Florida cost $3.2 million and caused significant harm to both animals and people [citation: CDC].