An outbreak of flesh-eating flies has been confirmed in South Texas, raising significant concerns for the state’s cattle industry. A sample taken from a three-week-old calf in La Pryor, Zavala County, tested positive for the first case of New World screwworm in the country, as announced by U.S. Department of Agriculture Secretary Brooke Rollins during a news conference on June 3.
To date, there have been no further detections of the pest. The USDA stated that personnel have been deployed to the area and are collaborating with local partners. They also reassured the public that the screwworm issue should not lead to immediate food supply disruptions, as these parasites do not infect meat, fruits, or vegetables.
Nonetheless, the USDA estimates that a screwworm outbreak could inflict $1.8 billion in damages to Texas’s economy. This potential crisis could also contribute to soaring beef prices nationwide, given Texas’s pivotal role in the cattle industry.
Understanding the New World Screwworm
The New World screwworm is a particular type of blowfly that lays its eggs in the flesh of living animals, rather than in carrion. Even minor injuries, such as a tick bite, can attract a female fly to deposit her eggs. A single female can lay between 200 to 300 eggs at once and may produce up to 3,000 eggs during her lifespan of 10 to 30 days.
The eggs hatch into maggots that burrow into the wound, feeding on living flesh. As larvae develop, they grow hooks that allow them to dig deeper into the tissue, which is how they earned the name “screwworm.” After approximately seven days of feeding, the larvae drop to the ground, burrow into the soil, and emerge as adult flies, perpetuating the cycle of infestation.
Infestations can involve multiple larvae stages within a single wound, often resulting in severe tissue damage due to a phenomenon known as a “feeding frenzy.” While screwworms typically infest mammals like cattle, pets, and wildlife, humans can also be affected.
Historically, the New World screwworm is indigenous to South America and some Caribbean regions; however, it has been gradually migrating northward since 2023, passing through Central America and Mexico. U.S. and Texas officials began monitoring cases the following year.
Concerns Among Ranchers and Agricultural Leaders
The presence of screwworm in an animal’s flesh can lead to significant wound damage, as the flies continue to invade, lay eggs, and exacerbate the injury, potentially resulting in illness or death. Even if the animal survives, there is often considerable harm to both its hide and overall health.
Cattle are particularly vulnerable to screwworm infestations due to their inability to adequately protect open wounds, and their larger bodies can allow for multiple infestation sites stemming from a single injury. “Texas livestock producers and all Texans must now be vigilant in their efforts to manage and combat the invasive pest,” stated Farm Bureau President Russell Boening following the confirmation of screwworm in Texas.
Although screwworms were eradicated in the 1960s, the U.S. faced a resurgence of the pest from 1972 to 1976, which resulted in tens of thousands of cattle infestations across six states and incurred significant containment costs. The issue was only resolved following an extensive eradication campaign.
With U.S. producers having not treated livestock for screwworm in over 40 years, the industry’s future now hangs in the balance. Texas leads the nation in cattle production, generating $15 billion annually for the state.
Preventive Measures Against Screwworms
In an effort to curtail the pest’s spread, the USDA closed the southern border to live animal imports in May 2025, restricting the entry of cattle from Mexico and consequently limiting the local supply in Texas. The federal government has allocated $100 million towards research, traps, and the deployment of patrol officers known as tick riders along the border.
U.S. officials are collaborating with counterparts in Mexico and Panama to eradicate the screwworm once again, utilizing the sterile fly technique. This method involves producing male sterile flies that mate with females, resulting in the laying of non-viable eggs. At the onset of the screwworm’s spread from Central America into Mexico, there was only one sterile fly production facility, located in Panama. Since then, another facility has been established in Metapa, Mexico, with plans for a third in Edinburg, Texas, expected to open in fall 2027.
Additionally, two fly dispersal facilities have been launched in Tampico, Mexico, and Edinburg to ensure the distribution of sterile flies where needed. The USDA has already begun dispersing sterile flies in South Texas, within a 50-mile radius of the border.
In response to the confirmed case, a quarantine zone has been established to regulate the movement and monitoring of animals in the vicinity. Officials are also increasing trapping and surveillance efforts for screwworm along the border, just beyond the dispersal area, and are stepping up monitoring of wildlife.
Signs of Infestation
Animal health experts emphasize the importance of regular monitoring and evaluation of livestock during a screwworm outbreak. Cattle producers and pet owners should remain vigilant for signs such as foul-smelling wounds with visible maggots, animals excessively licking or biting at wounds, lesions, and unusual behavior including restlessness or lethargy.
The most effective way to identify screwworm larvae is by observing the spikes that protrude from their bodies. Residents in affected areas are urged to check their pets for indicators of screwworm infection, including infected wounds and the presence of eggs or larvae.
Addressing screwworm infestations typically requires the manual removal of larvae, wound cleaning and dressing, and the application of veterinarian-prescribed pesticides. Individuals who suspect a screwworm infestation should report it to a local veterinarian or wildlife biologist.
“If we all work together and follow the animal treatment protocols and movement restriction guidance, there is no reason to believe that this incursion will result in an establishment of the pest in our country,” Rollins stated.
