It might sound like a plot from a horror film, but US officials are gearing up for a real-life battle against a flesh-eating parasitic fly, by releasing hundreds of millions of sterilised screwworm flies from aircraft over affected regions. The initiative, reported by CNN, is part of a growing effort to stop the spread of the New World screwworm, a deadly parasite that’s been moving steadily north through Central America and has now reached southern Mexico, sparking alarm among US ranchers and agricultural authorities.
To contain the threat, the US Department of Agriculture (USDA) is fast-tracking plans to build a new "fly factory" near the Texas–Mexico border, where sterilised male screwworm flies will be mass-bred and then released to disrupt reproduction in wild populations. The goal: flood the skies with sterile males that mate with wild females, resulting in no offspring and a gradual population collapse.
This isn't the first time such a tactic has been used. A similar biological warfare strategy helped eliminate the pest from US soil decades ago.
A parasite that devours living flesh
The New World screwworm, the larval form of the fly Cochliomyia hominivorax, stands out even among parasites. Unlike typical maggots that feast on decaying material, these larvae consume the flesh of living warm-blooded animals.
“After mating, the female fly finds a living host, lands on its wound, and will lay up to 200 to 300 eggs,” said Dr Phillip Kaufman, head of the entomology department at Texas A&M University, in remarks to CNN.
Once the eggs hatch, the larvae burrow into the flesh of the host using razor-sharp mouth hooks, causing deep wounds, severe infections, and in many cases, death if not treated quickly. While cattle are the most common victims, wildlife, pets, and even humans can be infected.
According to CNN, more than 35,000 screwworm infestations have been reported in Central America since early 2023, primarily in livestock, based on data from the Panama–US Commission for the Eradication and Prevention of Screwworm (COPEG).
“Fighting flies with flies”
The core of the strategy to halt the screwworm’s advance lies in sterile insect technique (SIT), a method in which male screwworm pupae are exposed to gamma radiation, sterilising them without impairing their ability to seek out and mate with wild females.
“The females only mate once in their lifetime, which makes the technique highly effective,” Kaufman explained to CNN.
Once released from aircraft flying over rural areas, the sterilised males compete with fertile wild males, reducing successful matings and gradually collapsing the parasite’s population.
Currently, there is only one facility in operation for producing these sterile flies — located in Panama. But with the parasite now pushing closer to the US border, officials say that additional capacity is urgently needed.
New facility planned for Texas
In response, the USDA has announced plans to establish a new fly production facility at Moore Air Base in Hidalgo County, Texas. The project, still awaiting final location and design approval, is expected to cost up to $300 million, CNN reported.
In addition to the Texas site, the US government has allocated $21 million to upgrade an older screwworm facility in Mexico, with the goal of making it operational by late 2025.
While the screwworm is most active during warmer months, US ranchers are already being urged to avoid branding, tagging, or castrating livestock during that time to minimise open wounds that could attract the flies.
There are no vaccines or reliable repellents currently available, making prevention and early detection crucial.
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