USDA to Build Sterile Fly Factory to Stop Flesh-Eating Maggots from Invading U.S.

The USDA is going to breed millions of flies, sterilize them with radiation, and send them into Texas and Mexico to prevent a re-emergence of the New World Screwworm(NWS), also known as a flesh-eating maggot. The NWS is endemic to Cuba, the Dominican Republic, and some South American countries, but it was eradicated in the US in 1966 using the sterile insect technique (SIT). NWS primarily targets and causes death to wild animals and livestock, which has caused tens of millions of dollars in losses for ranchers in the southern US before eradication.

There has not been an outbreak in the US, but the insect has been moving north into southern Mexico, crossing a biological barrier created in Panama with the SIT as part of the Commission for the Eradication and Prevention of Screwworm (COPEG), which was established in 1994.

Female screwworms lay eggs in open wounds of warm-blooded animals, including cattle, deer, dogs, and sometimes humans. Any animal with an open wound in an outbreak area is susceptible to potential infestation from the flesh-eating maggot, which would also cause an estimated $1.9 billion in agricultural losses in Texas alone. In the 1950s, before the eradication of the NWS in the US, ranchers had to inspect their livestock for open wounds daily.

Once the female lays eggs inside an open wound, the maggots proliferate and often cause death to the host animal. Michael Bailey, president-elect of the American Veterinary Medicine Association, said, “A thousand-pound bovine can be dead from this in two weeks.”

Females can only mate once in their lifespan, so sending sterilized males to mate with females is the technique employed to reduce the growth of the population. Male screwworms cannot cause an infestation because that only occurs when female screwworms lay eggs. It is considered a safe technique for animals, humans, and the environment to stop the proliferation of the destructive insect.

In May, USDA Secretary Brooke Rollins suspended imports of live cattle, bison, and horses across the southern border. There have been detections of screwworms in Oaxaca and Veracruz, Mexico, which is just 700 miles from the US border. Infestation of the host animal allows the screwworm population to travel long distances and relatively short periods.

The USDA plans to have a screwworm factory running in southern Mexico by July 2026. A Texas distribution center is expected to be opened by the end of 2025 to receive imported flies from Panama, if necessary.

“The United States has defeated NWS before, and we will do it again,” Secretary Rollins said last month. “We do not take lightly the threat NWS poses to our livestock industry, our economy, and our food supply chain. The United States government will use all resources at its disposal to push back NWS, and today’s announcement of a domestic strategy to bolster our border defenses is just the beginning. We have the proven tools, strong domestic and international partnerships, and the grit needed to win this battle.”

Rollins and the USDA laid out a five-pronged plan to address the threat posed by the northern migration of the screwworm. The first prong is to partner with Mexico to stop the spread of the screwworm. This includes a $21 million investment to renovate a production facility in Metapa, Mexico. This facility will produce 60-100 million sterile flies per week in addition to the 100 million produced weekly in Panama.

The second prong of the plan is to assist Mexico in trapping and tracking along the southern border, which they refer to as a “barrier zone of vigilance.” APHIS will send “cattle fever tick riders” to “intercept and treat stray and illegally introduced livestock.”

Prong three is ensuring there are appropriate NWS treatments available in the event of a domestic outbreak. The fourth prong is building a domestic sterile fly production facility at Moore Air Base to distribute sterilized flies to northern Mexico. The facility is expected to be completed by the end of 2025 with a potential production of 300 million flies per week.

The fifth prong is training locals in Texas, Arizona, and New Mexico to trap and surveil. The USDA is also working to improve and expand technologies that can provide additional support in eradication efforts.

The International Atomic Energy Agency says the sterile insect technique is environmentally friendly because it does not involve genetically modifying insects or using pesticides. The insects are irradiated in a controlled environment to make them sterile and sent out into the environment to mate with females. This stops the breeding without introducing non-native species into the environment