The threat from carnivorous maggots known as the New World screw worms forced the Agriculture Bureau to suspend imports of live cattle through the southern border.
The US suspends import of live animals due to carnivorous parasites
New World Screwworms have now brought the US to halt the import of all living animals from Mexico indefinitely. Females lay eggs on the open wounds of warm, bloody animals, and eggs hatch in a few hours.
Fox-10 Phoenix
US Secretary of Agriculture Brook Rollins said she has stopped importing livestock “monthly” through the Mexican border “monthly” to protect US cattle from the threat of invasion of dangerous, carnivorous parasites.
Parasites are New World Screwworms, or NWS, and are actually fly, which were eradicated in the United States almost 60 years ago. The US Department of Agriculture said in a statement on May 11 that the NWS was recently detected on a remote Mexican farm within 700 miles of the US border. The statement cited “NWS’ unacceptable northward advancement,” saying additional action should be taken.
“Due to the threat of screw bugs in the New World, I am quickly announcing the import of cows, horses and bison that have lived through the entrance to the US tropical border,” Rollins said in a social media post. “It took our cattle industry 30 years to recover when this devastating pest invaded America. This cannot happen again.”
Luis Fernando Halo, chief of Mexico’s Agricultural Council, said the ban was not necessary and “it doesn’t solve the problem.” He said the established protocols already ensure that cattle that travel to the US are “guaranteed to be released from screwworms.” Mexico’s Agriculture Secretary Julio Verdegu said he opposed the ban but hoped that the two countries would soon reach an agreement.
Rollins called the protection of American animals and the security of the country’s food supply “the most important national security issue.” As increased surveillance and eradication efforts begin to show positive results, the border will resume for livestock trade, she said.
“This is not about Mexican politics or punishment, but rather about food and animal safety,” Rollins said.
According to the USDA’s Animal and Plant Health Testing Agency, the USDA eradicated the NWS parasites in 1966 by ultimately leading to infertile flies to release sterile male flies and pups.
In November 2024, the United States stopped importing Mexican livestock after warning the US of detecting NWS cattle at a testing checkpoint near the Mexican border with Guatemala. The USDA then increased delivery of infertility flies, supported additional surveillance programs, and livestock imports resumed in February this year.
But last month, when Mexican authorities began cutting USDA planes’ seven-day flights and began cutting seven-day flights, imposing import duties on “critical aviation parts, distributed equipment, and infertile fly cargo,” Rollins said in a letter to Mexico’s Esteban Garden Barragan.
Mexico temporarily avoided the ban by allowing additional flights and reaching the transaction to waive customs duties.
Parasites get their name from the way maggots that produce larvae scar and open them when feeding animals, and “do great damage by tearing host tissue with sharp mouth hooks,” says USDA’s Animal and Plant Health Testing Service.
Adult screwworm flies resemble or slightly larger than a typical housefly, but have orange eyes, a metal blue or green body, and three dark stripes along their back.
The NWS does not regularly occur or spread in the US, but is usually found in South America and the Caribbean. People who travel to these areas, spend time among livestock animals, sleep outdoors, and suffer open wounds are at a higher risk of contracting the NWS.
