Residents of a small Chiapas town took to the streets again on Thursday to demand the relocation of the sterile fly production plant used to control the New World Screwworm (NWS).

Protesters in Metapa de Domínguez have complained about the smell emanating from the plant since it began operating in June. Locals describe the foul odor as akin to rotting meat and say the plant’s proximity to homes and schools poses a health risk.

En #Metapa, #Chiapas, pobladores protestan y exigen la reubicación de la planta de moscas contra el gusano barrenador, construida por #México y #EUA. Acusan grave contaminación, daños a la salud y afectaciones a la vida cotidiana. https://t.co/F2lzS8yvcH

— Cheché Torres (@Chechetc) October 15, 2026

They ended a three-day sit-in in early September after government officials agreed to address their complaints.

Residents told Reuters that the smell now regularly wafts across the town, even disrupting classes at nearby schools.

Mercedes Becerra de la Cruz, a local truck driver, said protesters want the plant relocated.

“We don’t care about the investment; we want this plant moved, because the smell is overwhelming,” Becerra told Reuters.

The protest comes less than four months after President Claudia Sheinbaum and U.S. Agriculture Secretary Brooke Rollins inaugurated the US $51 million facility, a key part of the bilateral effort to ​halt a screwworm outbreak that has disrupted the cross-border cattle trade since November 2024.

The Mexican government described the sterile fly plant as critical to protecting Mexico’s livestock industry, public health, the environment and the food sovereignty of both nations.

Millions of pest flies are raised inside the controlled, biosecure laboratory, where their larvae are fed a nutrient-rich mixture (e.g., eggs, milk and powdered hemoglobin) that mimics an animal’s open wound. The pupae, or adult flies, are treated with radiation to make them sterile.

Because female screwworm flies mate only once, mating with a sterile male results in no offspring, eventually crashing the wild population.

Sterile flies are the main defense against screwworm, a parasite that burrows into the flesh of warm-blooded animals and can be fatal if untreated.

As the smell has worsened, reaching ranches several kilometers away, residents said the government has not kept its September promises leaving them no choice but to protest again.

“We hope the commitment to reduce the fetid odors will be fulfilled no later than Dec. 16, otherwise we might be forced to undertake road blockades and other pressure tactics,” one resident told Diario del Sur newspaper.

With reports from Reuters, Diario del Sur and Forbes México