Devastating New World screwworm back on agriculture radar
This is the New World screwworm fly. It is about twice the size of an average housefly and can be identified by its large orange eyes and metallic green-blue coloration. U.S. Department of Agriculture photo
Texas is on high alert due to the potential threat of the New World screwworm, a once-eradicated, flesh-eating pest that devastated the U.S. cattle industry throughout the 20th century. While the parasitic fly seemingly hasn’t made it to Burnet County, local agriculture experts say awareness is key to stopping an outbreak.
The United States shut down cattle, horse, and bison trade with Mexico on May 11 when the screwworm was detected about 700 miles from the border. Since then, a coalition of local, state, federal, and international organizations have mobilized to control the insect’s spread before it can cause mayhem for ranchers north of the border.
“I wouldn’t say that we need to get panicked or scared right now; I just think that we need to be aware,” Burnet County AgriLife Extension Agent Kelly Tarla told DailyTrib.com. “Screwworms are definitely something that every livestock owner and every pet owner should be looking for.”
While Burnet County is far from the screwworm detection zone, Tarla said local ranchers should be vigilant.
“We are still rural enough where this could become a problem,” she said. “Believe me, if it comes close to a problem, we will be on top of it.”
The New World screwworm fly (Cochliomyia hominivorax) is native to the tropical regions of the Western Hemisphere. The fly lays its eggs near open wounds on a warm-blooded animal—including livestock, wildlife, and pets—that then hatch into larvae, or maggots, and burrow like a screw into the flesh of the host, causing massive damage and often death.
The fly was effectively eradicated in the United States in the 1980s, but not without some devastating consequences. In 1976 alone, the Texas economy lost about $329.59 million due to livestock deaths from a New World screwworm outbreak. Accounting for inflation, that would have been $1.8 billion in 2024. About 1.48 million cattle were reportedly infected in that outbreak.
The fly was a problem in the United States for decades, first becoming a threat in the 1930s, although it had been in the American Southwest since at least 1842. Eventually, scientists discovered a method of eradication: the Sterile Insect Technique. This was done by releasing massive numbers of sterilized male flies into infected areas, leading to infertile eggs and breaking the screwworm’s breeding cycle.
“There is a full generation between the guys who eradicated (the screwworm) and those who will be fighting it now,” Tarla said. “My grandad fought it, my dad didn’t, now I may have to.”
Since eradication in the 1980s, screwworms have had a minimal impact on U.S. ranchers, but even the threat of a potential outbreak is enough to raise the alarm. The U.S. Department of Agriculture estimates a screwworm outbreak could cost the Texas cattle industry $1.8 billion in annual losses and up to $10.6 billion in national economic damages.
U.S. Secretary of Agriculture Brooke L. Rollins suspended all trade of cattle, horses, and bison between the U.S.-Mexico border in May, and that order was reinforced in July.
To preemptively combat the screwworm threat, Texas is scrambling to bring a massive fly breeding facility online to once again implement the Sterile Insect Technique.
The Texas Farm Bureau is pushing for federal aid in the immediate construction of the SIT facility, which is planned in the Rio Grande Valley along the state’s border with Mexico.
“We cannot afford to wait. The New World screwworm is advancing, and the consequences of inaction are staggering,” Texas Farm Bureau President Russell Boening said in an Aug. 1 media release. “Secretary Rollins and her team have laid a strong foundation, and now we must build on it. A domestic sterile fly production facility is not just a strategic priority. It’s an emergency necessity.”
RESOURCES
Burnet County AgriLife Extension Agent Kelly Tarla recommends treating open wounds on livestock or pets as soon as they appear. If wounds seem to not be healing, or maggots are found in an open wound, she recommends contacting a veterinarian immediately to identify a potential screwworm infestation.
Contact the Burnet County AgriLife Extension Office at 512-756-5463 or kelly.tarla@ag.tamu.edu for more information.
Texas A&M AgriLife Extension has an online resource portal to help combat the potential spread of screwworms, including livestock management strategies, screwworm identification guides, and more.