Flesh-eating pests are coming. US plans to counter them by releasing millions of flies from planes

Picture this: Hundreds of millions of flies being dropped from planes. It sounds incredulous — almost like something from a horror movie. But, in fact, the US government actually plans on breeding flies and then dropping them from aircraft in efforts to eliminate a flesh-eating parasite that targets cows and cattle.

US Agriculture Secretary Brooke Rollins announced on Wednesday (July 9) that the federal government would release millions of sterile male New World screwworm flies into the wild to mate with females and prevent them from laying the eggs. This plan —essentially fighting flies with flies — will help to protect the more than $100 billion US cattle and beef industry from the New World screwworm.

What do we know of this plan? How will it work? We get you all the answers.

Fighting flies with flies

The US plans to build a fly-breeding facility in Texas near the Mexico border at a cost of $8.5 million in order to combat the menace of New World screwworm (NWS) flies. The new US dispersal facility is expected to be located at the Moore Air Base in Hidalgo County, Texas.

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Interestingly, this will be the second such facility in the Western Hemisphere, joining one in Panama that had largely kept the flies from migrating further north until last year. “The United States has defeated NWS before, and we will do it again,” Rollins was quoted as telling a news conference at the South Texas air base with other state and cattle industry officials.

Federal officials state that the factory will propagate millions of sterile male screwworm flies and those will be released into the wild. These male flies will then seek fertile females and help prevent them from laying eggs.

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But how will this plan work?

The idea behind it is mass sterilisation. In the 1950s, the US government came up with the Sterile Insect Technique, a method that utilised radiation to sterilise male flies. These sterile males were then released into the wild wherein they mated with the female, resulting in unfertilised eggs. Female flies mate only once, so if they pair with a sterile fly, they will be unable to reproduce. No fertile eggs meant no more screwworms.

The success of the programme — in 1966, the US officially eradicated the insect, protecting its cattle and beef industry — resulted in similar ones being created for mosquitoes too.

As Edwin Burgess, an assistant professor at the University of Florida who studies parasites in animals, told NBC News, “It’s an exceptionally good technology. It’s an all-time great in terms of translating science to solve some kind of large problem.”

Additionally, it is also more effective and environmentally friendly than spraying copious amounts of pesticide into the air to eradicate this pest.

About the ‘flesh eater’ New World Screwworm flies

New World Screwworms, scientifically known as cochliomyia hominivorax, is a devastating pest. It draws its name — screwworm — owing to its feeding behaviour as they burrow (screw) into the wound, feeding as they go like a screw being driven into wood.

According to Dr Phillip Kaufman, a professor and head of the department of entomology at Texas A&M University, what sets them apart from other flies is that they feed on the flesh of living animals — mostly cows and horses — rather than dead ones.

In some cases, New World Screwworm flies have infected domestic pets and even humans. In fact, the US Centers for Disease Control and Prevention has advised that individuals in the affected areas who “spend time among livestock animals, sleep outdoors and have an open wound are at greater risk of becoming infested with [New World Screwworms].”

They are endemic to Cuba, Haiti, the Dominican Republic and some South American countries.

Experts note that these flies cause extensive damage by tearing at the hosts’ tissue with sharp mouth hooks. The wound can become larger and deepen as more maggots hatch and feed on living tissue. As a result, NWS can cause serious, often deadly damage to the animal. In drastic situations, the flies can also kill an animal in a matter of one to two weeks and spread to others, posing a threat to the livelihood of ranchers.

Dr. Michael Bailey, president-elect of the American Veterinary Medical Association, even told USA Today, “This can kill a 1,000-pound cow in two weeks.”

New infestation moving towards the US

Since 2022, years after its eradication from the US, the New World screwworm has once again spread northwards through several countries in Central America. Cases exploded in Panama in 2023 and the fly had reached Mexico by November 2024.

Scientists have said that there are a number of reasons for this — higher temperatures enhancing fly development and survival, and the possibility that females are adapting their sexual behaviour to avoid sterile males.

Around 17 million cattle are now at risk in Central America, but the worse is yet to come. Mexico has twice as many cattle, and the spread towards the US continues, where around 14 million cattle would be at risk in Texas and Florida alone.

In fact, the US has responded by restricting live animal imports from Mexico, a move denounced by President Claudia Sheinbaum. She said that fears of the worm were overblown, pointing out that a single case in the eastern state of Veracruz had prompted the import pause. “From our point of view, it is a totally exaggerated decision to close the border again,” Sheinbaum said.

With inputs from agencies