The threat comes from the larvae of a fly species called Cochliomyia hominivorax, known as New World screwworms.
These flies lay their eggs in open wounds of live animals—especially cattle, horses, and domestic pets.
The eggs hatch within 12–24 hours, and the larvae eat the animal's living tissue, creating deep and fatal wounds. If left untreated, an animal can die within one to two weeks.
This harmful species has spread since 2023 to Panama, Costa Rica, Honduras, Guatemala, Nicaragua, Belize, and El Salvador. By November 2024, it reached southern Mexico, triggering alarm from the U.S. Department of Agriculture (USDA). Animal trade ports near the border have been shut down.
The U.S. is reactivating an old but effective strategy to fight the infestation:
Sterile male flies will be produced, released from airplanes, and will mate with wild females, resulting in unfertilized eggs. Since females mate only once, this method gradually eliminates the fly population.
The U.S. successfully used this strategy in the 1960s and '70s. Today, only one facility exists in Panama, which produces 100 million sterile flies per week. However, much more is needed to control the outbreak.
On June 18, the USDA announced the establishment of a new fly production facility near the U.S.-Mexico border. Production is planned to take place at Moore Air Base. The initial phase of the project is estimated at $8.5 million, but the total cost could reach $300 million.
In addition, an old facility in Mexico is scheduled to be refurbished by the end of 2025 with a budget of $21 million.
