A little‑known group of government cowboys called “tick riders” has quietly patrolled the southern U.S. border for over a century. The highly skilled cowboys, officially known as “Mounted Patrol Inspectors,” act as a living biosecurity fence between American livestock and a range of dangerous pests. Originally assembled as a frontline defense against cattle fever ticks, their mission has expanded to include other emerging threats, such as “New World screwworm,” which has now actually entered the US.
From what I’m understanding, the New World Screwworm re-emerged in the US after a decades-long absence when an infestation was recently confirmed in a calf in La Pryor, Texas, about 100 miles (161 kilometers) southwest of San Antonio and 50 miles (80 kilometers) from the U.S.-Mexico border. The flesh-eating parasite naturally migrated north across Mexico after a biological containment barrier in Central America was breached. Over the course of a year, the parasitic flies migrated approximately 1,100 miles from southern Mexico to the Texas border. A joint US-Panama program successfully established a biological barrier to contain the flies, but it was breached at the Darien Gap.
Historically, in the 1930s, the screwworm spread from the Southwest to the Southeast when producers unknowingly transported infested livestock across state lines. The US successfully eradicated the fly in 1966 using sterile insect techniques, but this new migration has triggered renewed federal surveillance and quarantine measures. Today, disruptions in the production and release of sterile flies (partially due to COVID-19-era supply interruptions), increased movement of livestock and wildlife, and difficult surveillance across remote terrain allowed the aggressive pest to spread unchecked northward.
I should note that government and industry officials are confident that they can contain the fly in the U.S. because the best method for eradicating the pest is both time-tested and highly effective: releasing sterile male flies into the wild. While males are “promiscuous,” in the scientific sense, females are not, and if their one mating hookup is with a sterile male, no eggs from that female will hatch. Once sterile males are prevalent enough — and millions a week can be released — the fly’s population declines and then dies out. The U.S. shut down its own fly factories after the pest was eradicated decades ago, leaving only an international breeding facility in Panama in the Western Hemisphere until the new one in Mexico opens. However, the USDA is also spending $750 million to build a fly factory in southern Texas that can produce up to 300 million sterile flies a week. Until then, let’s hope our “Tick Rider” Cowboys can help reduce the number of cases that get over the border…
Who the Tick Riders Are – Tick riders are mounted patrol inspectors employed by USDA’s Animal and Plant Health Inspection Service (APHIS) under the “Cattle Fever Tick Eradication Program,” launched in 1906. Working mainly in a permanent quarantine zone along the Texas–Mexico border, they ride horseback through river bottoms, brush country, and ranchland from Brownsville to roughly Del Rio, Texas. Their original mission was straightforward but demanding: find stray or smuggled livestock that might be carrying cattle fever ticks, and keep those animals from introducing parasites and disease into U.S. herds. In practice, that means long days in the saddle. Tick riders scout for cattle, horses, and other livestock that appear out of place. The strays are secured and brought to inspection points where veterinarians and technicians can conduct detailed checks for ticks and other external parasites. They also work closely with local ranchers inside the quarantine zone, enforcing movement controls and coordinating treatment so compliant producers can move cattle while still protecting the broader industry.
A Biosecurity Role with Real Economic Stakes – The stakes are high. Cattle fever ticks can transmit bovine babesiosis and anaplasmosis, diseases that cause severe anemia, weakness, and often death, with knock‑on effects for calf crops, feedyard performance, and export eligibility. The United States eradicated established cattle fever ticks by 1943, but the parasites and the diseases they carry remain entrenched in Mexico, which is why the quarantine zone and mounted patrol never went away. Analyses from USDA and industry groups consistently frame tick control as a nine‑figure protection effort, preventing potential losses that could run into the hundreds of millions or more if the pests regained a foothold in U.S. herds. Tick riders effectively extend the border for animal health purposes. By intercepting and treating cross‑border livestock before they mingle with domestic cattle, they provide early detection and rapid response capacity that is difficult to replicate with fixed infrastructure alone. In a region where terrain is rough, fencing can be patchy, and livestock routinely move with wildlife and people, that combination of mobility and local knowledge is a critical operational advantage.
Taking on New World Screwworm – Recently, the same mounted patrol has been tapped to help manage another serious threat: New World screwworm (NWS), a flesh‑eating fly whose larvae burrow into the wounds of living animals. In 2025, with NWS detected in parts of Mexico, APHIS expanded the tick riders’ mandate. Under a new protocol, cattle and horses apprehended in the Permanent Quarantine Zone are now automatically treated with NWS‑preventive products in addition to undergoing routine tick inspection and acaricide treatment. The goal is to ensure that any animal crossing the border illegally is not just tick‑free, but also less likely to be carrying screwworm eggs or larvae in open wounds. Because NWS targets wounds—from branding marks to tick bites, navels of newborn calves, and reproductive orifices—tick riders’ close, hands‑on inspections are particularly valuable. Riders are being trained to flag suspicious lesions, unusual discharge, or maggot activity and to fast‑track those cases to veterinarians and APHIS officials for confirmation and rapid response. (Sources: USDA, Texas Monthly, NPR, Modern Farmer)
