A notoriously destructive insect once eradicated from the United States is seeing a resurgence in Mexico – and ranchers are worried that it will soon cross the border to wreak havoc on their livestock.
It’s called the New World screwworm. This metallic blue-green blowfly’s maggot burrows deep into the wounds and crevices of warm-blooded animals – including people – to feed on flesh.
“If these infestations are left untreated, they can actually cause the death of an animal within 7 to 14 days,” said Dr. Samantha Holeck, who is the state veterinarian for New Mexico.
Estimates vary, but U.S. Department of Agriculture economic impact reports show the fly caused anywhere from $50 million to $100 million of damage annually before it was eradicated.
The insect was eliminated from the U.S in the 1960s after the government invested heavily in “sterilized fly” facilities that bred millions of male screwworm flies for release into the wild. Scientists discovered they could zap the flies with radiation, effectively stripping the bug’s ability to reproduce.
This helped whittle down the screwworm’s population significantly because the female fly breeds just once – and if they mate with one of the sterilized male flies, they die without producing offspring.
Fast forward 60 years later, hundreds of infected livestock cases have been documented from outbreaks in Northern Mexico, just under 60 miles from the Texas border. In response, the U.S. has closed all southern ports of entry to livestock trade.
“I think we're going to be hard pressed to keep it out of the United States at this point,” Holeck said.
Holeck pointed out sterilized fly facilities have been running “at capacity” for a long time now, and welcomes new efforts by the Trump administration to combat the fly. However, she is really worried about infected animals that can freely cross the border.
“We can't go out and mass treat wildlife to protect them or stop the spread of infestation,” Holeck said. “And monitoring wildlife can be challenging because they don't necessarily want to see people.”
She said the state has been planning its response for about a year with several different agencies – including the New Mexico Department of Health, Department of Wildlife, and the Livestock Board – but it has yet to release any drafts to the public.
When asked about specifics, Holeck told KUNM they are primarily building out early warning communication systems, sample collection kits, and weighing the use of game cameras to monitor animal hotspots.
Still, multiple agencies say the most important part of their strategy is to use frontline resources to quickly educate the public when the pest eventually arrives.
Darren Vaughan, a spokesman for the newly renamed Department of Wildlife, which is responsible for regulating, conserving, and protecting the state’s wildlife and their habitat, didn’t offer much information about a screwworm plan other than they were “keeping their eye” on the situation.
“We're definitely interested in monitoring the spread, because whatever preventative measures we are able to make will ultimately protect those wildlife and livestock populations going forward,” Vaughan said.
Vaughan did say they were coordinating with federal agencies, such as the U.S. Department of Fish and Wildlife and U.S. Department of Agriculture, and handing out information pamphlets to hunters and anglers, but he could not pinpoint what wildlife management actions would be taken if outbreaks start to pop up.
He was also “unsure” of any conversations between New Mexico and other border states like Texas, and Arizona to monitor screwworm among wildlife.
That approach worries Erica Valdez. She owns and operates the J O Bar Ranch in Animas in New Mexico’s southwestern boot heel and thinks it will be up to folks like her to keep the worm at bay.
“It should be a major concern to anybody, really, anywhere, but those of us that are within 50 miles of the border are going to get hit with it first,” Valdez said.
Valdez is not quite sold on the effectiveness of trail cameras or worm education efforts because they seem to have minimal impacts. Injuries from screwworms can vary from as small as a pinprick to as big as a basketball.
As for the game cameras, the area that would need to be monitored is just too big. The state alone shares 180 miles of border with the northern Mexican states of Chihuahua and Sonora, some of which is dominated by extremely remote, rugged desert and mountain country with very few paved roads.
“I don't think the [Department of Wildlife or U.S. Fish and Wildlife Service] have any type of action plan if it does come here,” said Valdez. “That's my biggest concern.”
Valdez breathes easier knowing her ranch follows an annual health management program to deworm and vaccinate their cattle. But she said that producers can be a “mixed bag” when it comes to physically checking up on herd health.
“What scares me is the smaller scale producers,” Valdez said. “It's more of a hobby, and they don't put the time and effort into maintaining that health program.”
The newfound resurgence of New World screwworm comes amid elevated beef prices and a historically tight domestic beef supply thanks to drought and high feed costs for ranchers like Valdez.
Coupled with the extended ban on live Mexican livestock imports and the ongoing war in the Middle East, prices are expected to surge even more by year’s end.
Currently, the average price for 100% ground beef is hovering at around $6.90 a pound, with nicer cuts of choice sirloin sitting at $14.44 per pound.
And with the New World screwworm on the march, there’s much more potential economic damage ahead.
