On April 30, 2025, U.S. Secretary of Agriculture Brooke Rollins announced in a press release that Mexico has committed to eliminate restrictions on USDA aircraft, and waive customs duties on eradication equipment aiding in the response to the spread of new world screwworm (NWS).

“I am happy to share Mexico has continued to partner in emergency efforts to eradicate the new world screwworm. This pest is a devastating threat to both of our economies, and I am pleased to work together with Mexico in good faith to protect the livelihoods of our ranchers and producers who would have been hurt by this pest,” said Secretary Rollins. “At USDA we are working every day to keep pests and disease from harming our agricultural industry. I thank our frontline USDA staff and their counterparts in Mexico for their work to ensure the screwworm does not harm our livestock industry.”

Historic infestations of the new world screwworm, a deadly parasitic fly, caused huge losses in the livestock industry. Unlike other fly maggots, the screwworm maggots feed on live animals rather than dead carcasses. Female screwworm flies lay their eggs in a wound, causing an infestation of maggots in the host animal, which can lead to severe complications and death.

The U.S. livestock industry benefits by more than $900 million a year according to USDA estimates, thanks to the eradication of the screwworm in the late 1960s. Should the NWS spread to the U.S. again, livestock, wildlife, humans and pets would all be susceptible.

The U.S. successfully led the previous eradication of NWS in the U.S. and Mexico, using sterilized male flies to reduce population numbers. Recent detections in Mexico show that this dangerous pest is back and the USDA considers NWS a serious threat.

According to an April 26 USDA press release, “Ongoing vigilance and control efforts are critical to prevent its spread northward and protect animal health and agriculture.”

ASKING FOR COOPERATION

On April 26, Secretary Rollins sent a letter to Mexico Secretary of Agriculture Julio Antonio Berdegue Sacristan, requesting cooperation in NWS eradication efforts, and stating that “if these issues are not resolved by Wednesday, April 30, USDA will restrict the importation of animal commodities, which consist of live cattle, bison and equine originating from or transiting Mexico to protect the interest of the agriculture industry in the United States.”

Mexican officials agreed to resolve the issues as Secretary Rollins requested, and ports currently remain open to livestock imports. If at any time these terms are not upheld, port closure will be revisited, according to the USDA.

Doug Tolleson, Texas A&M associate professor at the Sonora Research Station located between Rocksprings and Sonora, Texas, commented on the NWS situation. That area, about an hour north of the Mexican border, was devastated by the screwworm outbreaks in the 1950s and 1960s.

“I’m in my 60s and people older than me who dealt with this on a day to day basis all tell me that it is not something we want to go through again,” Tolleson said. “If we can keep that facility operating in Panama 24-7, 365, that’s our first line of defense. There are logistics that need to be overcome and we need to have a political climate that allows that to happen; if we can accomplish these things we probably have a good chance to keep that insect at bay.”

SERIOUS SITUATION

While Tolleson believes there is no need to panic, he considers the risk of screwworm arriving in the U.S. is serious.

“People on the front lines, including veterinarians are telling us they are on their way. It’s when, not if, and it will take a concerted effort to prevent severe outbreaks of screwworm,” he said.

Other factors, such as illegal transport of people and animals across the border, increase the risk of NWS spreading. Changes within U.S. agriculture may make a new infestation harder to control than previous outbreaks.

“It will be a much different situation if we have these pests coming in now,” Tolleson said. “We have less experienced ranch labor available now than in the past. People say that during the screwworm outbreaks was when we had the best ropers and the best rope horses; that’s what they did all day. Now we don’t have as many people who can do that work.”

Agricultural land is more fragmented now, and more ranch owners are long distance, living in cities rather than being actively involved in the daily operations. These factors could also play into delays in detection of NWS preying on livestock, and increase the speed of the spread of these pests, he said.

Any little injury makes an animal more susceptible to NWS predation.

“At birth, they often go after the navel of a calf, lamb or kid,” Tolleson said. “Bucks dropping antlers or even a tick bite can be an avenue for flies to exploit.

While colder weather in northern states in the U.S. should prevent outbreaks of NWS, movement of animals could put livestock further north at risk.

“If we have an outbreak, I think the line is going to push farther north than it was in the past,” Tolleson said.

Texas & Southwestern Cattle Raisers Association, the largest and oldest livestock association in the Southwest, commended Secretary Rollins’ efforts to hold Mexico accountable for its failure to manage the growing threat of NWS.

“As our neighbor, Mexico has fallen short in its role as a partner in managing the spread of NWS, placing the burden and risk disproportionately on the U.S.,” said TSCRA President Carl Ray Polk Jr. “We continually advocate for proactive efforts to manage NWS before it reaches the U.S. border, and welcome the support and consequences put in place by Secretary Rollins that can spur needed action to protect America’s cattle industry, food supply and wildlife populations.”

According to a press release, the association had boots on the ground in Panama at the world’s only large-scale sterile fly production facility in early April, 2025. This facility provides the sole defense against the spread of NWS across North and South America. Flies that came from this facility have inconsistently been denied access in certain parts of Mexico for dispersal flights.

“Mexico has tools at their fingertips, and to not allow aerial drops of sterile flies is irresponsible,” said Polk. “Texas will be the first to face the consequences of their inaction, and cattle raisers need strong leadership from USDA like Rollins’ demonstrated [on April 26] to push back against their failures.”

TSCRA is actively championing the creation of a U.S.-based sterile fly production facility and continues to collaborate with federal and state leaders to deliver proactive solutions to combat the eminent threat of the NWS.

USDA/APHIS reported that NWS was confirmed in a cow on Nov. 22, at an inspection checkpoint in the southern Mexico state of Chiapas, near the Guatemalan border. USDA subsequently prohibited imports of animals originating from or transiting through Mexico to protect U.S. livestock and other animals.

On Feb. 1, 2025, USDA/APHIS announced that cattle and bison imports from Mexico were scheduled to resume, following an agreement between APHIS and Mexico on the implementation of a comprehensive pre-clearance inspection and treatment protocol to ensure safe movement and mitigate the threat of NWS.