Mexico Opens a Fly Factory to Fight a Parasite That's Eating Cattle Alive

Deep in the jungles of southern Mexico, a new factory is pumping out millions of flies. Not the kind that buzz around your picnic. The sterile kind. The kind that Mexico and the United States are betting on to save a $5 billion cattle trade.

President Claudia Sheinbaum inaugurated the facility on Friday, a joint project between the Mexican government and U.S. agricultural authorities. The plant sits in Chiapas, Mexico's southernmost state, and it represents the most aggressive move yet to wipe out the New World screwworm, a parasitic menace that has shut down live cattle exports from Mexico to the United States.

The screwworm is not an insect you want near your cattle. Female flies lay eggs in open wounds on warm-blooded animals. When the larvae hatch, they burrow into the flesh and feed on living tissue. An untreated infestation kills an animal within days. It was officially eradicated from North America in the 1960s using the same technique the Chiapas plant is deploying now.

But the parasite never truly disappeared. It held on in South America and crept back up through Central America in recent years. By late 2023, Mexican authorities detected screwworm cases in cattle near the Guatemala border. The U.S. Department of Agriculture responded by halting live cattle imports from Mexico, a decision that froze a cross-border livestock trade worth billions.

The result? Mexico started shipping more packaged beef instead of live animals, with exports jumping 23 to 30 percent. But that is a workaround, not a fix. Ranchers on both sides of the border want the border open again.

How Sterile Flies Fix a Parasite Problem

The science is simple on paper. The Chiapas facility breeds screwworm flies by the millions. Males are separated from females and hit with a low dose of radiation, enough to sterilize them but not enough to stop them from flying, mating, or acting like normal flies. Then they get released over infected areas. They mate with wild female screwworms. The eggs never hatch. Over successive generations, the wild population collapses to zero.

It is called the Sterile Insect Technique, or SIT. It worked in the 1950s and 1960s when the U.S. and Mexico teamed up to kick screwworm out of North America the first time. It has been used successfully against fruit flies, tsetse flies, and mosquito populations around the world. The Chiapas plant is basically a reboot of that old campaign.

Sheinbaum said the facility is already producing, though the first phase is modest.

"El viernes vamos a Chiapas a inaugurar la planta, ya con su primera producción," Sheinbaum told reporters. "Es la primera fase y después va a ir aumentando el número de ejemplares que se van a producir."

Translation: Friday we go to Chiapas to open the plant, already with its first production. This is the first phase, and then the number of specimens produced will keep increasing.

It Takes Two to Fight a Parasite

This is not Mexico's problem alone anymore. Screwworm has now been detected on U.S. soil, making it a shared crisis. The parasite crossed the border despite the import restrictions. That changes the math. What was once a Mexican livestock issue is now an American one too.

Sheinbaum pushed for a more structured response. The current cooperation happens through informal channels between agricultural agencies. She wants something formal.

"Lo que nosotros hemos propuesto es que se haga una comisión formal binacional," she said. "Así se hizo en su momento cuando México y Estados Unidos vivieron una situación de esta plaga."

A formal binational commission, like the one that worked during the original screwworm eradication campaign decades ago. It is a proposal that cuts through the noise. The two countries are locked in fights over tariffs, immigration, fentanyl, and energy policy. But screwworm does not care about any of that. A parasite in Chiapas cattle can be in Texas cattle within weeks.

The U.S. funded a significant portion of the Chiapas plant. Mexican workers staff it. Mexican scientists run the breeding and sterilization operations. But the investment came from both sides of the border, a rare spot of collaboration in a relationship that has been anything but smooth.

What This Means for Your Plate

For international readers, the stakes are concrete. Mexico is the top beef supplier to the United States. When live cattle can't cross the border, the supply chain bends. More packaged beef gets shipped, which keeps grocery stores stocked, but the margin tightens in ways that eventually hit the checkout counter.

If the sterile fly program works and the screwworm population collapses, live cattle imports can resume. The $5 billion trade lane opens back up. Prices stabilize. And the method becomes a blueprint for how two countries that cannot agree on much can still cooperate on science.

If it fails, the parasite keeps spreading. More U.S. livestock gets infected. The import ban stays. And the beef supply chain stays under pressure.

The plant in Chiapas is the first phase. Production will ramp up gradually as more sterile flies are bred and released across the affected zone. No one is pretending this is a quick fix. Eradication campaigns take years, not months. But the facility is running. The flies are being made. And for the first time in a while, Mexico and the United States are working on the same side of a problem.

The screwworm does not know about tariffs. It does not care about trade disputes. It just eats cattle alive. And two countries that cannot agree on much have decided that the parasite is the enemy worth fighting together.