Key Moments
- A New World screwworm infestation was confirmed in a Texas calf after the parasite spread north through Mexico.
- U.S. cattle imports from Mexico have been halted for the past year, intensifying record-high beef prices amid a historically small domestic herd.
- The USDA estimates a potential screwworm outbreak could cost the Texas economy $1.8 billion in livestock losses, labor, and treatment costs.
Threat Emerges as Screwworm Crosses Long-Standing Barriers
New World screwworm, a destructive parasite that consumes the living tissue of cattle and other warm-blooded animals, has moved north from Central America into Mexico and was confirmed in a Texas calf on Wednesday, according to experts. The insect has pushed beyond biological defenses that had constrained it for decades.
In response to its advance deeper into Mexico, Washington has blocked imports of Mexican cattle for the past year. That move has tightened already scarce U.S. cattle supplies and contributed to record-high beef prices by preventing Mexican calves from entering the domestic production system. The newly confirmed U.S. case in Texas marks a significant escalation in the current outbreak and introduces fresh risks for ranchers and beef markets.
Understanding New World Screwworm
Screwworms are flies that parasitize any warm-blooded animal by laying eggs in open wounds. Livestock and wildlife are the most frequent hosts. After the eggs hatch, hundreds of larvae bore into living flesh with sharp mouthparts, enlarging the wound as they feed. If left untreated, the infestation can kill the host.
For cattle, seemingly minor injuries – such as small scrapes, recent branding marks, or healing ear tag sites – can quickly transform into large, maggot-filled lesions that endanger the entire herd. The United States eliminated screwworms in the 1960s using a strategy that relied on releasing huge numbers of sterilized male flies. These sterile males mate with wild females, resulting in infertile eggs and collapsing the local screwworm population.
Potential Impact on U.S. Consumers and Beef Prices
The United States normally brings in more than one million head of cattle from Mexico each year. The current import ban has added upward pressure on beef prices by further restricting the supply of animals available to U.S. packers, at a time when drought has already driven the domestic herd to a multi-decade low.
Mexican cattle are typically sent to U.S. feedlots, where they are fed and finished for five to six months before slaughter. Reducing the flow of these animals can lower slaughter volumes and push beef prices higher.
A larger U.S. screwworm outbreak would tighten cattle supplies even more and extend the threat to other livestock species and household pets. Screwworms can also infest humans. Dr. Timothy Goldsmith, a veterinary medicine professor at the University of Minnesota, said that homeless individuals would be particularly at risk, as they sleep outside and have less access to hygiene products and medical care.
Current Response and Control Measures
A dedicated plant in Panama that breeds and sterilizes screwworm flies is releasing 100 million sterile insects each week. However, experts indicate that additional production capacity would have needed to ramp up quickly to prevent the parasite from advancing northward.
In the United States, a sterile-fly production facility in Texas is scheduled to start operating in late 2027. The U.S. Department of Agriculture (USDA) finished building a separate dispersal facility in Texas in February.
Sonja Swiger, an entomologist at Texas A&M University, noted that individual screwworm flies are unable to travel more than 12 miles on their own. Even so, they can move much farther when embedded in animal hosts. The insect has already traversed the narrowest sections of Panama and Mexico, which, according to experts, now requires exponentially larger numbers of sterile flies to contain the outbreak.
In a related effort, the USDA last year committed $21 million to convert an existing fruit fly plant in Mexico into a facility that can produce sterile screwworms.
| Control Measure | Location | Status / Scale |
|---|---|---|
| Sterile screwworm production and release | Panama | Releasing 100 million sterile flies per week |
| Sterile fly dispersal facility | Texas, U.S. | Dispersal facility completed in February |
| Sterile fly production facility | Texas, U.S. | Expected to open in late 2027 |
| Conversion of fruit fly factory to screwworm production | Mexico | $21 million USDA investment announced last year |
Economic Stakes for Texas Ranchers
The USDA projects that a screwworm outbreak could inflict $1.8 billion in costs on the Texas economy, including losses from livestock deaths as well as increased labor and medication expenses. After many years without the parasite, most ranchers lack the hands-on experience and specialized tools needed to recognize and treat screwworm infestations.
While infestations can be treated, the process is demanding: it requires physically extracting hundreds of larvae and thoroughly cleaning and disinfecting the affected wounds. That makes control efforts costly, time intensive, and labor heavy.
“This is a pest we don’t want back. This is a bad thing,” said David Anderson, livestock economist at Texas A&M University. “I can’t imagine having to deal with that. It’s gross.”
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