(Note: this article contains graphic photos)
It is a real-life horror movie. A small parasitic fly about the same size or slightly larger than a common housefly, but with orange eyes and a metallic blue or greenish body, lays eggs on an open wound of a warm-blooded, living creature. While feeding on flesh, the larvae (maggots) live up to their name of New World Screwworm by screwing or burrowing deeper into the wound with sharp mouth hooks. As more eggs hatch, the larvae feed on more living tissue. If not discovered and treated, the victim will suffer severe wounds and/or die.
The U.S. Department of Agriculture (USDA) confirmed that horror movie migrated north into southern Texas about 60 miles east of the Mexican border and 90 miles west of San Antonio. On June 3, it reported a three-week-old calf is infected in Zavala County, the first such case in the U.S. in decades, followed by another reported cow infection two days later in the same county. Then on June 7, it confirmed a positive screwworm calf infection in nearby La Salle County and on June 8, a cow in La Salle County, a goat in Gillespie County west of Austin and another in a dog in Lea County, New Mexico, in the state’s southwest corner. The USDA believes that case is an isolated one because the dog’s travel and exposure history is not known.
“Protecting our livestock industry is a national security issue of the utmost importance, and USDA is wasting no time in taking action,” said USDA Under Secretary for Marketing and Regulatory Programs Dudley Hoskins. “USDA invested heavily in the tools needed to eliminate NWS (screwworm) ever since cases started increasing in Central America and Mexico. The United States has defeated this pest before and we will do it again.”
The USDA deployed a command team to work with the Texas Animal Health Commission where it set up 12.5-mile infested zones around the detections and implemented quarantines, movement controls and surveillance. Officials say they are releasing sterile screwworm flies from the ground as a defense measure, in addition to the four million sterile flies it has already been releasing aerially along the U.S.-Mexican border every week since February. When produced and released in mass, sterile male flies mate with wild female flies which then lay unfertilized eggs.
For more than a year, USDA led a unified response to screwworms by deploying advanced surveillance systems and supported cross-border response efforts in Mexico and Central America to combat the pest and push screwworms away from the United States. These efforts bought time for USDA to increase domestic preparedness efforts.
Health officials say the threat to humans is very low but those that are most susceptible work closely with livestock.
National Food Supply
The USDA says the nation’s food supply is safe as screwworms do not infest meat, fruits, vegetables or other food sources. Its Food Safety and Inspection Service works to ensure the nation’s commercial supply of meat, poultry and egg products is safe, and assures that any evidence of screwworms would be identified during inspections.
“This pest does not cause any sort of a food safety issue. It is not a disease but simply an insect that feeds on living tissues,” said Brooke Rollins, USDA secretary. “Animals treated early enough will recover and are safe to enter the food supply system.”
Where Screwworms Live
New World screwworms are found throughout South America (except Chile) and in six Caribbean countries: Aruba, Cuba, Dominican Republic, Haiti, Jamaica and Trinidad and Tobago. Since 2023, screwworms re-emerged in previously pest-free regions, including all the countries in Central America and Mexico, where there have been more than 171,700 cumulative screwworm cases reported in animals and more than 2,070 cases in people.
Screwworms in the United States – a Past History
Known to be an issue in the southwestern United States since at least 1842, health officials first documented the screwworm as a significant problem in 1933 following shipments of infested livestock from the Southwest to the Southeast. Following the development and release of sterile male flies, the U.S. declared the threat eradicated in 1966. Since then, there have been several outbreaks in the Southwest (1972) and Florida Keys (2016-17), all of which were successfully combated. In 2025, the U.S. Department of Health and Human Services confirmed a person who traveled to Maryland from Guatemala was the first human case in America. The patient received treatment and fully recovered.
Why This Matters to Hunters
According to the USDA, deer and other species are vulnerable to screwworm infestation, which can reduce the number of fawns that survive and grow into adults. Untreated infested animals will die, leading to smaller herds, fewer tags and more restrictive seasons. Affected animals may lead to compromised meat quality, deformities on hides and antlers, and stunted growth and reduced antler development. If a larger outbreak were to occur, below are things that could happen, as per the USDA:
Click here for more information about the New World screwworm.
About Hunt 2 Conserve
Hunt 2 Conserve is a 501(c)4 nonprofit organization affiliated with the Rocky Mountain Elk Foundation. Its mission is to advance a legacy of hunting and conservation by educating, activating and developing stewards and defenders of these fundamentally American ideals. For more information, go to hunt2conserve.org.
(Photo credit: USDA/COPEG)
