The cattle industry in Texas is facing a significant threat from the New World screwworm, a flesh-eating fly that has recently been detected in South Texas. This infestation has raised concerns about the potential economic impact and the well-being of tens of thousands of cattle in the state.
The first case of New World screwworm in the country was confirmed in a 3-week-old calf from La Pryor in Zavala County. The U.S. Department of Agriculture (USDA) has activated personnel on the ground and is working with local partners to manage the situation. While the infestation does not directly affect the food supply chain, it poses a serious risk to the cattle industry and could lead to a rise in beef prices nationwide.
The nature of the screwworm threat
The New World screwworm is a type of blowfly that lays its eggs in the flesh of living animals. A single female can lay 200 to 300 eggs at a time and up to 3,000 eggs during her 10- to 30-day lifespan. The eggs hatch into maggots that burrow into the wound to feed on living flesh. These larvae develop hooks and dig deeper into the flesh, hence the name screwworm. After feeding for about seven days, the larvae drop to the ground, burrow into the soil, and emerge as adult flies, repeating the cycle of infestation.
Multiple infestations are common, with multiple stages of larva in one wound, sometimes leading to a feeding frenzy that results in rapid tissue damage. The screwworm is typically found in South America and parts of the Caribbean but has been moving northward since 2026. Federal and Texas officials have been monitoring cases, and the infestation has now reached Texas.
Impact on cattle and other animals
The screwworm infestation poses a significant threat to cattle, which are particularly susceptible due to their inability to protect open wounds. The infestation can cause extensive damage to the hide and health of the animal, and even if the animal survives, there is usually extensive damage. The Texas Farm Bureau encourages pet owners to check their animals daily for wounds and monitor for signs of infestation, as dogs and cats are particularly vulnerable.
Although human cases are uncommon, they can occur, especially after someone has visited a place where the fly thrives, such as South America, Cuba, Haiti, or the Dominican Republic. Even small injuries can provide an entry point for screwworms on a human. Preventative measures for humans include keeping wounds clean and covered and wearing loose-fitting, long-sleeved clothing and socks.
Efforts to combat the infestation
The USDA has invested $100 million into research, traps, and mounted patrol officers known as tick riders at the border. U.S. officials are working with officials in Mexico and Panama to eradicate the screwworm again, using the sterile fly method. This practice involves producing male sterile flies to reproduce unviable eggs with female flies who can only mate once in their lifetime.
The sterilization method was successful for more than 20 years, with a key facility in Panama. However, the flies suddenly overpowered the insect barrier and the difficult terrain of the Darien Gap in 2026. The exact cause of this breach is unclear, but scientists believe it is most likely due to multiple factors, including interruptions in sterile fly production caused by the COVID-19 pandemic and illegal cattle imports stemming from surveillance gaps in geographically difficult regions.
In response to the first confirmed case, the USDA implemented a quarantine zone, controlling the movement and surveillance of animals in the area. Officials are also increasing trapping and surveillance for screwworm along the border, just outside the 50-mile dispersal area, and are ramping up surveillance and monitoring of wildlife.
The U.S. Food and Drug Administration (FDA) has issued multiple emergency orders authorizing topical sprays, powders, injectable drugs, and ointments to treat New World screwworm in various animals. Texas Agriculture Commissioner Sid Miller has criticized the USDA’s response to the threat of screwworm as slow, bureaucratic, and incomplete, urging President Donald Trump to direct the agency to deploy the Screwworm Adult Suppression System.
Animal experts say continual and regular monitoring and evaluation of all livestock are important during a screwworm outbreak. Cattle producers and pet owners should be alert for signs of infestation, which include foul-smelling wounds with visible maggots, animals biting or licking at wounds, lesions, and unusual restlessness or lethargy. Treatment for screwworm often involves the manual removal of larvae, cleaning and dressing the wound, and prescribed pesticides by a veterinarian.
