Illicit Movement of Livestock, Drug Cartels & the New World Screwworm

Introduction

The New World Screwworm (NWS) is not a disease or virus, but a fly whose parasitic larvae (maggots) feed on tissue of warm-blooded animals, including livestock, wildlife, and pets. Female flies lay eggs on wounds and any bodily openings of animals and then these eggs hatch into larvae that burrow into flesh. This can cause seeping wounds, severe tissue damage, and even death in animals if left untreated. Though the NWS can cause severe damage to livestock and wildlife, the food supply is safe and will continue to be protected by a litany of longstanding and effective safety protocols that ensure this parasite that only affects living animals is caught and removed and that it never reaches an American plate.

While America’s food supply is safe, the recent reemergence of the NWS in the U.S. is enough of a threat to livestock, wildlife, and America's farmers and ranchers that it requires a significant response from state and federal governments and the private sector. The NWS has existed across large swaths of the Americas from ancient times to present, and with the exception of a handful of isolated instances, the NWS has been successfully eradicated from the U.S. for decades. In 1966, through years of mass-releasing sterile male flies that mate with wild females, producing no offspring, the U.S. government eliminated the fly and then expanded the fight to Mexico and Central America. For decades, a biological barrier was maintained in Panama at the Darien Gap via ongoing sterile fly production and release.

The NWS Moves Northward & America Responds

Despite decades of eradication, the NWS resurged northward from the Darien Gap starting in 2021, with officials warning of its arrival in late 2024, and models predicting it to reach the U.S. by 2025. Thanks to the United States Department of Agriculture (USDA) and its partners, the insect was kept out of the U.S. for more than a year beyond even the latest predictions of its arrival time to the U.S. In some of her earliest remarks as the Secretary, USDA Secretary Brooke Rollins re-alerted the public to the threat and with federal, state, and private-sector partners, began implementing a comprehensive, end-to-end plan. This plan is now in full rollout informing a comprehensive response operation, which includes the lockdown of the southern border to live animal imports, the ongoing breeding and releasing of millions of sterile flies, trapping and surveillance along the border, proven wildlife management strategies, and several other actions proven to reduce the incidence of the NWS.

This response spans federal and state government, as well as the private sector. For instance, the Department of Health and Human Services (HHS) has responded through the streamlining and acceleration of emergency use authorizations and conditional approvals for drug products to prevent and treat larval presence in all manner of animals. The Department of Homeland Security (DHS) has led through providing border security, intelligence, and preparedness components, with Customs and Border Protection (CBP) playing the most prominent role. This has included enhanced monitoring at the southern border’s ports of entry to prevent NWS-infested animals from entering the U.S. and their training of over 23,000 frontline CBP personnel protecting borders and other key locations on NWS for identifying and dealing with this pest. In addition to these efforts, the Department of State, Environmental Protection Agency (EPA), and the Departments of Energy and Interior, as well as other federal agencies, have all stepped forward to proactively plan and respond.

The Darien Gap and the Root Causes of the NWS’ Movement

Despite the current administration’s all-of-government response efforts, previous leaders’ immigration and crime policies at and south of the southern border continue to enable NWS's steady advance north. In a June 2, 2026 stakeholder call, Secretary Rollins stated:

"The Darien Gap, the dense jungle separating South and Central America, served as both a geographic and a biological barrier. Limited movement of people, livestock, wildlife, and commerce through that region slowed the northward spread of pests and diseases and helped keep the new world screwworm largely contained in South America."

She continued that "increased cartel activity and other political pressures lessened the control officials had on the area" and said the barrier protecting North America "had been breached."

The NWS was eradicated from the U.S. by 1966, from Mexico by 1991, and from Panama by 2006. Since 2006, the USDA and its partner agencies have maintained a “living barrier” in the Darien Gap by continually releasing sterile flies. The remoteness of this natural land bridge separating North and South America, and the dense, mountainous rainforest-type landscape, has allowed authorities to ensure that, functionally, no (i.e., just a handful of cases per year) incursions of animals with new eggs were hatching from that point northward for the last 20 years.

Decades of successful, sustained efforts kept the NWS south of the Darien Gap. Then, in 2021, on U.S. leaders’ watch, the quarantine failed, and the NWS became established in thousands of animals. This spread extends north of the Panama Canal. Calendar year 2023 saw expansion of reported cases of the insect throughout Central America and in 2024, the NWS had moved with livestock far north, well into Mexico.

The Illicit Movement of Livestock Hastens the NWS Arrival in the U.S.

Before 2021, the Darien Gap was a biological barrier against NWS because of the continuous aerial release of sterile flies. By 2025, the Darien Gap and the area at large, with already rough and difficult-to-control terrain, became neglected and instead evolved into a nonstop highway for illegal migration, illicit livestock movement, and the drug trade. Also, checkpoints elsewhere in Panama, as well as in other locations in Central and South America, shifted from identifying and stopping this threat facilitating the movement people and goods faster. This occurred in Panama, through the use of government-funded buses to facilitate transfers to the Costa Rica border. At the same time, NGOs operating in the area, including the Red Cross, were providing illegal immigrants with maps and resources to continue northward, further enabling the flow rather than restricting it. Long-standing weak governance, difficult terrain, and a lack of genuine political will or capacity to secure these routes allowed known trafficking routes to not only increase in volume of people, but also of illicit goods passing through unchecked. This situation also allowed cartels to gain greater control. These harms increased despite the at least superficial security commitments given to the U.S. and other partners by Central and South American governments to police these routes.

The reemergence of NWS near the U.S. is the result of years of failed border security policies in the U.S. and a broader breakdown in enforcement across the Western Hemisphere. While this is seen most clearly in and around the Darien Gap, weakness toward transnational criminal organizations and unchecked

smuggling networks caused conditions that allowed this threat to move north. Drug and crime transport risks for the U.S. are also illicit livestock movement risks when south of the border. When illicit livestock are moved, they create significant biosecurity risks, including the spread of insects like NWS. Previous U.S. administrations failed to hold these governments accountable for these activities and, in effect, encouraged these illicit activities northward by leaving the U.S.-Mexico border largely open. At the same time, U.S. officials promoted the use of the Border Patrol's CBP One mobile app—an immigrant-facing scheduling tool with location-based functionality—to seek asylum appointments. That app was later shown to have exploitable location vulnerabilities that cartels systematically used to secure appointments for migrants who were thousands of miles from the border. Criminal migration and smuggling of people created pathways and new demand that also facilitated illicit livestock movement across the border.

How Drug Cartels Drive the Illicit Movement of Livestock and the Spread of the NWS

The illicit movement of livestock, from Central America into Mexico is a major driver of NWS’s northward spread. This connection is found in agriculture at large in Mexico, where cartels tighten their grip on crops like avocados, limes and tomatoes and then use those industries to launder capital and control territory. The livestock version is cattle are regularly smuggled and illicitly sold in unregulated, cross-border movements from Central American countries into Mexico and cartels control the value chain. Their activities bypass sanitary inspections and customs controls and launder otherwise contraband animals into Mexico’s legal supply chains. The activity is reportedly so rampant with livestock that it has corrupted Mexico’s cattle registration system. Cartels now sell official cattle ear tags on the black market for $20-35 each – well above the legitimate registration price of roughly $2.50 – which are then applied to Central American contraband cattle at Mexico’s southern border. Smugglers then use these fraudulently obtained ear tags alongside falsified documents to move these contraband animals north past additional checkpoints. An estimated 800,000 cattle are smuggled into Mexico each year, generating up to $18 million per year for the operating cartels.

InSight Crime and the Wildlife Conservation Society have documented these patterns. In a November 2024 release, the Wildlife Conservation Society stated the following:

"Major screwworm outbreak hotspots closely mirror cattle smuggling routes... Illegal cattle trade follows transboundary routes starting in Nicaragua and passing through Honduras and Guatemala, before infiltrating Mexico's food supply chain, allowing the parasite to travel nearly 700 miles in just two and a half months."

Beyond the lack of enforcement and fraud at border crossings and checkpoints, other known drug trafficking routes branch from Nicaragua through Honduras and Guatemala and directly into Mexico's food supply chain. These crime maps and routes have been a known threat for many years. Less known are the activities of criminal networks coordinating transport across borders, and that profits from drug trafficking and other illicit activities get directly washed through legitimate-seeming businesses like the production and transport of cattle. These existing patterns of smuggling and other trafficking match the

NWS’s known insect and spread of animal patterns. In short, cartels do not merely profit from the illicit movement of livestock south of the U.S. border, they also govern it. They control routes, regulate movement, corruptly skirt inspections, scam registration systems, and ultimately launder high-risk livestock into Mexico’s legal supply chain.

Mexico’s Lack of Cooperation in Combatting Crime Guides the NWS to the U.S.

New World screwworm does not move north on its own; it moves with infested animal hosts. Since July 2021, many of those host cattle have moved through the same illicit corridors that traffic drugs, and people. The northward spread of NWS is therefore tied directly to the criminal smuggling networks operating across Central America and Mexico. Despite this direct connection, Mexico has been uncooperative on ending this illicit livestock movement and on the NWS response overall. There have even been recent assassinations of two prominent livestock industry leaders in Mexico, signaling the arrival of drug cartel violence to its cattle ranching and livestock industries. In June 2026, Agustín Morán, president of the Asociación Ganadera de Cuajinicuilapa in Guerrero (a local livestock association), was reportedly ambushed and killed alongside his wife. In April 2026, Lina Alejandra Rodríguez Castillo, national secretary of Mujeres Ganaderas de México (Women Cattle Ranchers of Mexico), was reportedly assassinated inside her business.

Starting last year, despite clear challenges in doing so, the U.S. has acted in good faith to work with Mexico to contain the spread of this insect, but Mexican authorities have continually limited intervention actions like sterile fly dispersal flights and imposed customs delays on critical eradication equipment. When the U.S. took actions such as suspending all livestock imports from Mexico last year, President Sheinbaum even called these actions “exaggerated” and “unfair.” But despite this lack of cooperation by Mexico, which has led to the continued movement of animals carrying the NWS northward, a robust plan for response from state and federal governments and the private sector in America has been underway for more than a year, and is now being activated.

Conclusion

With only about 25 cases per year reported at the Darien Gap separating North and South America pre-2021, the U.S. maintained a strong barrier against the NWS for decades. Prior U.S. leaders’ open border policies and neglect of countering crime and illegal immigration activity in South America took the Darien Gap from a controlled containment point and biological barrier to the NWS into a superhighway for the insect to make its way northward on its animal hosts. The millions of known migrant crossings officially reported from 2021-2024, as well as countless live animals crossing checkpoints that were left wide open have resulted in the 18,000+ NWS cases reported in Panama (plus thousands more reported northward). The arrival of the NWS in livestock in America in June of 2026 is certainly a cause for alarm, but should not have been a surprise to any close observers.

The Trump Administration is fighting this insect on every front. Of note, the southern border was closed over a year ago and remains closed to all live animal imports that can carry the NWS. The closure

of the border, coupled with historic investments in sterile fly breeding and release programs, wrap-around surveillance and testing, and wildlife monitoring programs, leaves the U.S. in as good a posture as it could be in to fight this insect. Had previous U.S. leaders taken border security, cartel activity, and livestock smuggling seriously, NWS could have been contained farther south through established international control efforts and sustained pressure on known trafficking corridors. Instead, prior leaders failed to hold regional governments accountable and created permissive conditions that encouraged illicit livestock being movement northward. Biological threats, cartel governance, and unsecured borders are no longer separate problems; they are interconnected Western Hemisphere security challenges. The U.S. must continue the approach championed by the Trump Administration from day; strong borders, aggressive action against cartels and criminal networks, robust international cooperation, and continued investment in the tools and technology needed to protect America's farmers, ranchers, livestock industries, wildlife, and the food supply.