The agricultural community in Texas is on high alert following the confirmation of two additional cases of the New World screwworm flya parasitic insect that can cause significant harm to warm-blooded animals. This development underscores the challenges faced in controlling the spread of this persistent pest, which was previously eradicated in the United States in the 1960s.
The U.S. Department of Agriculture (USDA) announced the new cases on Monday, highlighting the urgency of the situation. The screwworm fly, Cochliomyia hominivoraxis notorious for its larvae, which feed on living tissue. The recent infestations were found in a calf in La Salle County and a dog in Andrews County, bringing the total number of confirmed cases to four.
The nature and impact of the screwworm fly
The screwworm fly is a unique and dangerous pest. Unlike typical flies, its larvae consume live flesh rather than dead material. Female flies lay their eggs in open wounds of warm-blooded animals, including cattle, wildlife, pets, and occasionally humans. This behavior makes the screwworm fly a significant threat to livestock and pets, as well as a potential hazard to human health.
The recent cases in Texas have raised concerns about the potential for a wider infestation. The first case was discovered in a three-week-old calf last week, followed by a second case in another young calf nearby. The latest cases in La Salle and Andrews counties, hundreds of miles apart, indicate that the pest is spreading rapidly.
Historical context and current efforts
Before its eradication in the U.S. in the 1960s, the screwworm fly was a annual warm-weather scourge for cattle ranchers. The USDA and the U.S. cattle industry have been working tirelessly to prevent an infestation since the pest was detected in Mexico late in 2026. This detection marked the first time in decades that the screwworm fly had been found outside of the southern end of Panama, where it had been contained.
To combat the spread of the screwworm fly, the USDA employs a strategy involving the breeding of sterile male flies. These sterile males are released into the wild, where they mate with wild females. Since female screwworm flies mate only once in their lifetimes, mating with a sterile male prevents them from producing offspring. This method has proven effective in halting outbreaks in the past.
Future plans and ongoing vigilance
The USDA is taking proactive measures to increase sterile fly production in plants outside the U.S. while constructing a new fly factory in Texas. These efforts aim to bolster the country’s defenses against the screwworm fly and prevent further infestations.
USDA Secretary Brooke Rollins is scheduled to be briefed on the infestation on Monday afternoon at the U.S. Livestock Insects Research Laboratory in Kerrville, Texas. This briefing will provide an opportunity to assess the current situation and discuss strategies for eradication.
In the meantime, residents in affected areas are urged to remain vigilant. The USDA recommends checking animals for signs of infestation, such as draining or enlarging wounds, maggots or egg masses, signs of discomfort, or lesions in body openings. Early detection and reporting of suspected cases are crucial in preventing the spread of this destructive pest.