TOPEKA, Kansas: In a campaign that sounds more like a science fiction plot than public policy, the U.S. government is preparing to breed billions of sterile flies and release them from planes over Mexico and southern Texas. The objective? To combat the deadly New World screwworm — a flesh-eating maggot that threatens to wreak havoc on livestock, wildlife, and even household pets.

Though bizarre, this approach has proven effective in the past. The targeted pest, the larval form of the New World screwworm fly, feeds on the living tissue of warm-blooded animals. Female flies lay their eggs in open wounds or mucous membranes, and once hatched, the larvae burrow into flesh, causing severe pain, infection, and — if untreated — death. A single infestation can kill a 1,000-pound cow in under two weeks.

To halt the fly's spread, the U.S. Department of Agriculture (USDA) will release millions of sterile male flies into the wild. These flies, irradiated to prevent fertility, mate with wild females, but no offspring are produced. Over time, the pest population collapses.

"It's an exceptionally good technology," says Edwin Burgess, an entomologist at the University of Florida. "It's one of the great scientific solutions to a large-scale problem."

This method of biological pest control — called the Sterile Insect Technique — was instrumental in eradicating screwworms from the U.S. and much of Central America by the late 20th century. A fly production facility in Panama, jointly operated by the U.S. and regional partners, has served as the front line of defense, keeping the flies contained in South America.

But in late 2024, the screwworm reappeared in southern Mexico, triggering alarms. In response, the USDA plans to expand production by building a new fly factory in southern Mexico by July 2026. Meanwhile, a fly distribution center will open in Texas by the end of this year to receive sterile flies from Panama if needed.

Historically, from 1962 to 1975, over 94 billion sterile flies were released in North America to drive the screwworm to extinction. One biological advantage makes this tactic potent: female screwworm flies mate only once in their short adult lives. Ensuring that the majority of them pair with sterile males effectively halts the reproductive cycle.

Still, the risk is real and immediate. In May, the U.S. temporarily closed its southern border to live imports of cattle, horses, and bison. It may not reopen fully until September. The screwworm can infect any warm-blooded animal — including humans — and its return would be a devastating blow to the beef industry.

Decades ago, the U.S. maintained fly-breeding facilities in Florida and Texas, but those closed after the screwworm was declared eradicated. Now, the USDA wants to scale up again, targeting production of up to 400 million sterile flies per week. This effort will involve US$8.5 million for the Texas distribution hub and $21 million to convert an old fruit fly facility in Mexico.

Producing flies isn't as simple as it sounds. Females must be induced to lay eggs, and larvae need a nutritious diet. Past diets included mixtures of horse meat and honey, and later, blood plasma and egg powder. Once mature, the larvae — resembling dark brown Tic Tacs — are packed into sawdust trays to pupate.

Even logistics carries risk. Last month, a plane distributing flies near Mexico's Guatemala border crashed, killing three crew members. Air drops, typically conducted with light aircraft, still use variations of mid-century methods — either paper cups or crates dispensed through mechanical devices.

Experts warn that once the pest is again under control, the infrastructure should not be dismantled. "Declaring total victory is tempting," says Burgess, "but nature has a way of surprising us. A pest like this can always return."