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New World Screwworm Map & 2026 Spread Predictions

Fri, 19 Jun 2026 19:18:53 GMT

As social media fills with maps and predictions about how far New World screwworm might spread this summer, many livestock producers are asking the same question: When will it get to me?

According to Cassandra Olds, Kansas State University Extension entomologist, that’s the wrong place to start. “I think everybody’s kind of bracing for when will it get to me, and I don’t think that we really know,” she says.

She argues producers should focus on how the pest moves and what management steps can slow it down or keep it out of their herds in the first place.

Meteorologist Matt Makens explains weather patterns act as both a barrier and bridge for screwworm activity. For producers, that may be the most important line to keep in mind through the rest of the warm season.

How Temperature and Rainfall Affect Screwworm Survival

Weather does not just influence screwworm activity — it helps determine where the pest can survive, reproduce and spread.

Makens explains temperature thresholds can dictate screwworm development. Pupa development cannot proceed below about 58°F and halts above 110°F, while adult survival and reproduction are most favorable around 81.5°F. That means much of the southern U.S. is warm enough during summer to support at least temporary fly survival and movement. But heat alone does not tell the full story.

“While temperature defines where screwworms can survive, rainfall and moisture influence when and how intensely they can thrive,” Makens adds. In other words, many areas may be warm enough, but not every area will be equally favorable.

For producers trying to judge risk, moisture may be the deciding factor.

“Outbreaks often follow moderate to heavy rainfall by improving conditions for larval survival,” Makens says. “When rainfall coincides with favorable temperatures, screwworm activity tends to increase.”

In contrast, hot and dry conditions tend to suppress survival and reproduction. That is an important distinction for livestock producers who may assume the hottest areas automatically face the greatest danger. Makens suggests the higher-risk zone is really where warmth and wetness overlap — especially where recent rainfall has improved soil moisture and where livestock are exposed through wounds or other openings attractive to egg-laying flies.

Makens stresses, “The fly can’t live without water and dry soil is no good for their larvae.”

That means producers should watch not only temperatures, but also rainfall patterns, wet soils, humidity and any shift toward a more tropical summer setup.

Screwworm Migration Patterns: The Role of the North American Monsoon

Weather can do more than create suitable habitat — it can also physically help move the pest northward.

“One of the primary ways to move the fly, other than animal transport, is the weather,” Makens says, pointing specifically to the North American Monsoon, describing it as “a dominant source of migration.”

That monsoon pattern generally develops from late spring into summer and shifts winds into a more southerly, moisture-rich flow across Mexico and into parts of the Southwest and southern High Plains. He adds wind-assisted movements created an atmospheric “conveyor belt” that, in past outbreak years, helped reconnect infestations in the Southwest with source populations farther south.

For producers, that means concern should not be limited to locations immediately adjacent to current infestations. If winds, moisture and temperatures line up, the pest could move well beyond the border region.

The broader weather pattern matters, Makens summarizes, but so does what is happening in each pasture and pen. Screwworm is most likely to move north not in a uniform wave, but in jumps — following corridors where heat, moisture and wind align.

Why We Can’t “Draw a Line” to Where Screwworm Goes Next

Olds says predicting screwworm migration with precision goes well beyond a simple climate map.

“To actually predict, you need fairly sophisticated models that take into account the number of eggs that a fly can lay, the number of flies in the population, how far a fly can move, animal movements and things like that,” she explains. “Realistically, it’s incredibly difficult to predict how fast it’s going to spread.”

Historic data gives rough guidance on how far the flies themselves can move.

“We have some data, right, like 0.75 to 1.25 miles a day is average dispersal in previous outbreaks,” Olds notes. “But that really depends on conditions and how big your population is.”

Landscape also matters. Olds says NWS flies don’t like to cross bodies of water, so major rivers and other barriers can slow natural spread. But those biological and landscape limits are only half the story.

How Livestock Transport Spreads Screwworm Outbreaks

In addition to natural fly dispersal, livestock movements can pick the parasite up in one region and plant it in another.

“To predict where it’s going to go really depends on whether you’ve got fly movement and animal movement, or a combination of both,” Olds summarizes.

In other words, trucks can leapfrog flies. That’s one of the biggest reasons no one can honestly tell a producer in Kansas, Oklahoma or farther north that “their turn” will come in a certain month or year.

“I don’t think it’s as easy as, yeah, Kansas will get it next year, or Oklahoma will get it next year, or next month,” she stresses. “The only way we know is once it starts behaving — once we can start watching it in Texas — then we can make predictions about how it may spread further out.”

How Producer Behavior Can Speed Or Slow Screwworm Spread

Human decisions might matter as much as weather and biology.

Olds warns failure to report infestations and comply with control measures could dramatically accelerate spread. That puts producers in the position of front‑line risk managers. Reporting and allowing treatment might be inconvenient, but Olds says it’s also the best way to keep the parasite from marching across the map.

Making Sense of Social Media Maps

(Texas Tested Seeds & Plants)

One viral graphic, pictured above, created by Beverly Thomas of Texas Tested Seeds & Plants attempts to predict the potential NWS range based on climate suitability and historical data.

Thomas admits she is not an expert: “I’m just reporting what’s happening and going by historical references.”

Her post says: “The threat is divided into two distinct biological zones…where the fly can live *permanently*, and how far north it can march during the warm months. The ‘Summer Dispersal Zone’ — NWS can reach Kansas, Missouri, Tennessee and further north via wind/livestock. The ‘Overwintering Zone’ where NWS could become permanently established in South/Central Texas & Gulf Coast areas due to mild winters. Winter is the ultimate limiting factor because screwworm pupae can’t survive hard, prolonged soil freezes. However, the winters of the 2020s are significantly milder than those of the 1950s when eradication began. The new reality is that the permanent, year-round survival zone is no longer confined safely to Southern Mexico. South Texas, the Lower Rio Grande Valley and the Gulf Coast could now be treated as year-round establishment zones. Many entomologists believe that warmer winter trends will allow the permanent NWS overwintering line to push into Central Texas and across the deep Southeast (Louisiana, Mississippi, Alabama, Georgia and Florida).”

Thomas’ map predicts:

Critical/Active Regions: South Texas, Lower Rio Grande Valley. High humidity and thick brush provide ideal habitat. The parasite can easily establish a year-round lifecycle here if not eradicated quickly.
High Risk Regions: Central/East Texas, Gulf Coast, Coastal Louisiana, Southern Florida. These areas are at high vulnerability for permanent establishment. Mild modern winters mean soil temperatures rarely drop low enough for long enough periods of time to kill burrowed pupae.
Moderate Risk Regions: Northern Texas (Dallas/Panhandle), Oklahoma, Arkansas. These areas have a high vulnerability for summer infestation. While winter freezes will reliably clear out populations annually, unchecked spring/summer migrations could trigger devastating seasonal outbreaks.

Olds reviewed the map and says it is directionally reasonable, but producers should understand what it is — and what it’s not.

“If you have a suitable climate and a way for the fly to get there, a population can establish,” she says. “Suitable climates are different than what they were historically because we’ve got changing climate conditions.”

She notes climate change and cattle movement mean today’s “at‑risk” zone may be broader than the historical endemic area.

“A large part of the United States is at risk. We know what it was historically. This may have changed because climate conditions are different now,” she says. “I don’t think this map is super alarmist, it’s probably close enough, as much as we can be at this early stage.”

For producers, that means maps can illustrate potential climate and geographic risk, but they don’t provide a day‑by‑day forecast for when screwworm will show up at the ranch gate.

Practical Risk Management: What Producers Can Do Now

Since no one can reliably answer “when,” Olds recommends reframing the question: How do I reduce the risk of introduction and spread in my herd and region?

She highlights three practical steps to reduce risk:

Control Movements Out of Infested Areas. “The management of risk is making sure we aren’t having cattle leave infested areas that have not been inspected because that’s the fastest way to get it to seed somewhere else,” she explains.
Inspect New Arrivals. “Monitor any cattle that you receive to make sure they don’t have it, so you’re curbing also the infestation,” she adds. That means working with veterinarians, checking animals closely — especially any wounds — and asking questions about origin and treatment history before cattle are commingled.
Track Confirmed Cases Through Official Channels. Rather than relying only on social feeds, Olds points producers to official reporting: “Watch the screwworm.gov website because they are going to report every single case, so then you’ll be able to gauge month by month, it’s moving here.”

She says following those steps allows producers to distinguish between natural fly expansion risk and introduction risk. For livestock producers in the Texas counties surrounding current outbreaks, she says the priorities are heightened vigilance and wound monitoring.

The Takeaway: Manage Risk Now, Don’t Wait for Certainty

The science isn’t yet able to offer producers a neat line on a map or a firm date on the calendar. But Olds’ message is that uncertainty about timing does not mean inaction.

While NWS’s exact migration path will depend on climate, flies, cattle movements and human behavior, producers can act now: Report cases, cooperate with control efforts, tighten biosecurity on cattle movements and stay current on official updates.

Or, as Olds puts it, instead of focusing on when, focus on: “What am I doing today to keep it from getting here at all?”

Inching Closer: New World Screwworm Now 52 Miles from Border

Fri, 29 May 2026 14:09:14 GMT

New World screwworm (NWS) continues to creep closer to the U.S.-Mexico border. According to Lyndsay Cole, chief of strategic communications NWS directorate for USDA-APHIS, Mexico has reported two new cases in Nuevo León that are about 52 miles away from the border and one was reported Wednesday about 55 miles away in Coahuila.

“There are no cases or suspect cases in the U.S.,” Cole stresses.

New World screwworm is NOT in the U.S. and @USDA continues to deploy proven technology and nationwide outreach to stay ahead of this pest and protect livestock, pets, wildlife, and people.

Preparedness starts with awareness, so get the facts: https://t.co/3qu43ITr1j pic.twitter.com/9Kpc3uxCdO
— USDA Animal and Plant Health Inspection Service (@USDA_APHIS) May 28, 2026

Current New World screwworm cases in Mexico as of May 28, 2026.

(USDA APHIS)

A Narrowing Buffer Zone

There are currently 2,072 active cases of NWS in Mexico. USDA continues to disperse 100 million sterile insects per week in Mexico and along the U.S.-Mexico border and closely evaluates the location and circumstances of each new case. The sterile insect release area, or polygon, is adjusted as needed to maintain broad suppression and help prevent the pest from moving into the U.S.

(Lori Hays)

Early Detection: The Stench of Infestation

As NWS inches closer, industry leaders urge producers to shift from worry to action. Early detection, prompt reporting and treatment — backed by coordinated surveillance along the border — will be critical to keeping the treatable pest contained.

Producers who have dealt with the pest often describe it as a smell you’ll never forget , noting that the stench of a calf infested with NWS is often the first warning sign.

The prevention and treatment playbook is already taking shape. Prevention means fewer wounds, tighter calving windows, stronger parasite programs and more “eyeballs” on cattle, backed up by early reporting and a vet-guided treatment plan.

When cases do occur, today’s toolbox — from prescription pour-ons and emergency-use injectables — can limit the damage, as long as producers know how and when to use each tool.

Border Awareness: CBP Issues Traveler Warnings

U.S. Customs and Border Protection (CBP) announced a public awareness campaign warning the South Texas traveling public about the threat of NWS on May 28. CBP Laredo Field Office developed an informational tearsheet in English and Spanish that advises about the threat of NWS and is distributing the tearsheet at the eight ports of entry from Brownsville to Del Rio, Texas, that comprise the Laredo Field Office area of responsibility.

“We are working to increase public awareness regarding New World screwworm so that the public can help prevent this invasive pest from reaching the U.S. and adversely affecting U.S. livestock and pets,” says Laredo Field Office Field Operations Director Donald R. Kusser. “By distributing these tearsheets and amplifying via social media, we are hoping to bring this message to the widest audience possible.”

NWS Resources

Visit Screwworm.gov for a wide range of stakeholder resources for livestock producers, veterinarians, animal health officials, wildlife professionals, healthcare providers, pet owners, researchers, drug manufacturers and the general public. It also has the latest USDA-verified information on cases and response activities in Mexico and U.S. preparedness efforts.

Your Next Reads:

How One Dairy is Using Embryos to Replace Jerseys With Holsteins

Thu, 23 Apr 2026 15:32:41 GMT

As milk markets evolve, some dairies are starting to pull back on Jerseys, driven by a combination of shifting milk pricing, weaker replacement demand and changing revenue opportunities beyond the bulk tank.

For some, that shift has meant leaning into crossbreeding to capture flexibility and hybrid vigor. For others, it has meant doubling down on Holsteins to produce more milk volume, capture stronger beef-on-dairy premiums and improve cull value. That has been the case for Triple G Dairy and LegenDairy in Arizona, where a closer look at whole-herd economics, not just components, has prompted a gradual move away from Jerseys and toward a more Holstein-focused system.

When Fairlife expanded into the state six years ago, it reshaped breeding priorities for several dairies. For Triple G Dairy and its sister operation, LegenDairy, the focus on higher components triggered a transition away from Jerseys and toward Holsteins.

(Skylar Gericke)

“When Fairlife came in, they said that they had their bottom line on components, and we needed to be above that number on protein and fat,” says Skylar Gericke, part-owner at LegenDairy. “We originally did not meet their threshold for components, but we are now well over past component tests from when we milked a mixed herd”.

At the time, the fastest way to raise components was to bring Jerseys into the system. Since then, genetics, nutrition and management improvements have helped the Holsteins catch up.

“When we built LegenDairy, we moved all the Jerseys to that location and focused the Holstein herd at Triple G,” Gericke says. “But now the Holsteins have come up in components. We’re around 3.3 protein and about 3.7 fat now. At this point, we’re really working toward a Holstein herd and phasing the Jerseys out.”

Looking Beyond Components

The decision to move away from Jerseys was not based on components alone. When Gericke evaluated the economics across the entire system, several factors began favoring Holsteins.

“We still ship milk to a fluid market,” Gericke says. “And with the way our Holsteins are milking today, I need to ship more hundredweights in order to spread that fixed cost.”

Additional revenue streams also played a role in the decision.

“The more and more you look into breeding, the Holstein cows are becoming more efficient,” Gericke explains. “And when you factor in beef-on-dairy calves, the beef calves have a $500 to $1,000 premium on them. Even culling those Holstein cows, you get another $300 to $400 per cow. So profitability wise, we’re better off Holstein.”

Replacement market signals reinforced that direction.

“There’s just no good market for Jerseys right now,” he says. “Everybody is either trying to get out or breeding them terminal.”

Read: Crossbreeding Gains Ground as Some Dairies Scale Back Jerseys

(Skylar Gericke)

How Embryos Are Reshaping the Herd

As the farm shifted away from Jerseys, LegenDairy used Holstein semen on Jerseys to create some crossbred animals. The focus was on high genomic Holstein bulls with strong udder and health traits.

“We went back through the bulls we had been using and looked at the calves that had already been genomically tested,” Gericke says. “From there, we picked the top performers based on udder traits and component levels, and those top three bulls were the ones we used on the Jerseys.”

But as Gericke dug deeper into the economics, he concluded that building a herd of more purebred Holsteins made the most sense. Embryo transfer became the main tool driving that change.

“We make our own Holstein embryos through IVF,” Gericke says. “It gives us control over the progress, and I like having that control.”

That approach has helped accelerate the shift toward a more uniform Holstein base by multiplying higher-end genetics and reducing reliance on natural turnover.

(Skylar Gericke)

Genetics Is a Long Game

While reproductive tools like IVF can speed up progress, genetic change still takes time to work through a herd.

“Once you start implementing a breeding strategy, you have to think long term,” says dairy consultant Jason Anderson. “Unless you’re selling your cows and buying a different breed, it can take five to seven years from the time you change the semen in the tank before that new herd is fully in place.”

That delay means breeding strategies must also align with milk markets.

“Having a clear understanding from your processor about what they want from your milk helps define your strategy,” Anderson says. “It’s important to know what they are looking for and how that fits with the breeding decisions you’re making on the farm.”

For Gericke, that long-term mindset is exactly why he has leaned into embryo transfer.

“We can make management changes pretty quickly, but genetics don’t move that fast,” Gericke says. “Embryos help us speed things up, but once you pick a direction, you still have to stick with it and let it play out in the herd.”

Next Step in the Screwworm Fight: USDA Announces Opening of Sterile Fly Dispersal Facility in Tampico, Mexico

Thu, 13 Nov 2025 21:50:03 GMT

USDA announced Thursday the opening of a sterile fly dispersal facility in Tampico, Mexico. The Tampico facility will allow USDA to disperse sterile flies aerially across northeastern Mexico, including in Nuevo Leon. This announcement is the next milestone in the fight against New World screwworm (NWS).

“The opening of the Tampico sterile fly dispersal facility is another incredibly important tool in our arsenal to stop the spread of screwworm. The facility will ensure flexibility and responsiveness in northern Mexico, giving us a greater ability to drop sterile flies and continue to push the pest south,” said U.S. Secretary of Agriculture Brooke Rollins in a press release . “Stopping the spread of screwworm is a top priority for the entire Trump administration.”

Last week Rollins met with Mexican President Claudia Sheinbaum and her counterpart Secretary Julio Berdegue on the joint response to NWS.

“We are boosting our efforts and completing a joint review of our screwworm operations in Mexico to ensure our protocols are being followed,” she says. “As we enter the winter months , we continue to prioritize the response in Mexico and the rest of our five-pronged plan to protect U.S. livestock and the livelihoods of American farmers and ranchers.”

A proven method for NWS eradication is releasing sterile male flies to mate with wild females collapsing the population over time. There are two methods of dispersing sterile insects – aerial dispersal and ground release chambers. Aerial operations are preferred because they allow for dispersal at a steady rate through a large area and also because sterile insects may be dispersed in areas that are unreachable from the ground. Ground release chambers are used when there’s a need to quickly deploy sterile insects outside of the dispersal facility range.

Learn more about NWS:
The Smell You’ll Never Forget: A Calf Infested with New World Screwworm

According to the press release, USDA continues to disperse 100 million sterile flies per week in Mexico, but until now, aerial operations have been limited to southern Mexico, necessitating the use of ground release chambers in more northern areas of the country. Mass production and targeted dispersal of sterile flies remain critical components of our effective response.

Although Mexico continues to confirm new cases of NWS, the overwhelming majority of these remain in the far southern part of the country, with no significant northward expansion over the past several months. Should that change, the Tampico facility will allow USDA to immediately tackle any cases that occur elsewhere in Mexico.

The two northernmost detections (approximately 70 and 170 miles from the U.S. border, respectively) occurred in Nuevo León, on Sept. 20 and Oct. 5 , in young cattle transported from Chiapas, Mexico.

Neither case is still active and there have been no additional detections of NWS flies in traps or cases in animals in Nuevo Leon. USDA continues to disperse sterile insects in Nuevo Leon, and will now transition from ground release chambers to aerial dispersal in those areas.

USDA produces sterile flies for dispersal at the COPEG facility in Panama. USDA is also investing $21 million to support Mexico’s renovation of an existing fruit fly facility in Metapa — which will double NWS production capacity once complete. With ongoing support from APHIS technical experts, Mexico anticipates this sterile fly production to begin as soon as summer 2026.

To expand our domestic response capacity, USDA has also begun construction on a sterile fly dispersal facility at Moore Air Base in Edinburg, Texas, that is projected to begin operating in early 2026. APHIS is also expediting design and construction of a sterile fly production facility in southern Texas, with a targeted maximum capacity of 300 million sterile flies per week.

USDA continues to work with Mexico’s agriculture authority, SENASICA, to implement the collaborative NWS Action Plan and guide trapping, surveillance and movement protocols to help stop the northward spread of NWS.

Trade Mission While In Mexico

While Rollins was in Mexico last week, she also led the largest U.S. Department of Agriculture agribusiness trade mission in history. During the mission, 41 U.S. businesses, 33 cooperators and agriculture advocacy groups, six state departments of agriculture, and 150 participants conducted more than 500 business-to-business meetings during the three days.

According to a USDA press release , “This was a critical opportunity for American business to further trade ties and for USDA to continue its aggressive response to NWS in Mexico and continue to hold Mexico accountable for its commitments to the 1944 Water Treaty.”

Honored to lead the largest @USDA Agribusiness Trade Mission in US history to Mexico City!

Over three days, our delegation of 41 US businesses, 33 cooperators, 6 state departments of agriculture, and 150 participants held more than 500 business-to-business meetings - deepening a… pic.twitter.com/39rGi9Snhj
— Secretary Brooke Rollins (@SecRollins) November 13, 2025

Your Next Read: Preparing for the Battle Continues: USDA Shares Screwworm Update and Releases NWS Playbook

Mistrial Declared in Arizona Rancher’s Murder Trial

Thu, 26 Sep 2024 18:42:44 GMT

An Arizona judge declared a mistrial in the murder case of rancher George Alan Kelly, 75, who was accused of fatally shooting a migrant on his property near the U.S.-Mexico border.

Superior Court Judge Thomas Fink said the decision was made after jurors failed to reach a unanimous decision after two full days of deliberation.

Following the declaration, Kelly’s defense attorney Kathy Lowthorp revealed outside the courthouse to the media that there had only been one guilty juror in the group, which was why the defense team pushed for deliberations to continue.

“There was one hold out for guilty, the rest were not guilty. So seven not guilty, one guilty,” Lowthorp stated. “We believe in our gut that there was no way the state proved beyond a reasonable doubt.”

Kelly had faced second-degree murder in the Jan. 30, 2023, shooting of Gabriel Cuen-Buitimea, 48, who lived just south of the border in Nogales, Mexico. Kelly had earlier rejected an agreement with prosecutors that would have reduced the charge to one count of negligent homicide if he pleaded guilty.

“It is what it is, and it will be what it will be. Let me go home, okay? That alright with y’all?” Kelly told reporters outside the courthouse following the mistrial. “I will keep fighting forever. I won’t stop.”

Judge Fink had told jurors that if they could not reach a verdict on the second-degree murder charge, they could try for a unanimous decision on a lesser charge of reckless manslaughter or negligent homicide.

The Santa Cruz County Attorney’s Office can still decide whether to retry Kelly for any charge or drop the case all together.

A status hearing was scheduled for next Monday afternoon, when prosecutors could inform the judge if they plan to refile the case.

Related:

Arizona Rancher Rejects Plea Deal in Death of Migrant

Arizona Border Rancher Accused of Killing Migrant, Now Held With $1 Million Bond

$200 Million Dollar fairlife Processing Plant to be Built in Arizona

Thu, 12 Nov 2020 05:53:22 GMT

By mid-2020 a new milk processing facility in Arizona will be producing fairlife dairy-based beverages.

On April 8, fairlife, LLC announced plans to build a 300,000 square foot production and distribution facility just outside of Phoenix , in Goodyear, Arizona. The plant would be fairlife’s second plant in the U.S., with the company already having a production facility in Coopersville, Michigan. Last June, fairlife and distribution partner Coca-Cola Company announced the addition of a production facility in Ontario, Canada , that added the first international market for the ultrafiltered milk products.

“I’m extremely proud that the demand for our milk has grown so much that we now need another manufacturing site! In choosing a new plant location, it is essential that the new facility be built in an area where dairy farms are willing and able to follow fairlife’s responsible animal care and sustainable farming practices while producing the highest quality milk. Not only are there amazing dairy farmers in and around Goodyear, its location enables competitive domestic and international production,” says Tim Doelman, chief operating officer for fairlife.

The new Arizona plant is projected to be operational in the second half of 2020 and is estimated to cost $200 million to construct. fairlife is working with United Dairymen of Arizona to source milk from area dairy farmers.

“fairlife is a pioneer in the dairy industry and having their new plant here will not only encourage innovation in Arizona, it will contribute to our efforts to grow our advanced manufacturing sector in our community,” adds Mayor Georgia Lord of Goodyear, Arizona.

fairlife was founded by dairy farmers Mike and Sue McCloskey in 2012 . The plant will process a number of fairlife products, including the different varieties of fairlife ultra-filtered milk, Core Power, fairlife YUP!, fairlife smart snacks, and fairlife nutrition plan.

“Sometimes, I think back to that day over 20 years ago when Mike and I sat at our kitchen table and came up with the idea of cold-filtering our milk for higher nutrition. We dreamt of a more nutritious milk for consumers. It is extremely rewarding to see the results of our hard work pay off and make this dream a continuing reality, thanks to the great dairy farmers here in Arizona. We look forward to working with all our amazing partners and are committed to supporting the economic growth in the southwest region,” says Sue McCloskey, dairy farmer and co-founder of fairlife.

The new processing facility will employ more than 140 people.

For more on fairlife read the following stories: