Flesh-eating screwworms spread to third state and are attacking pets

As Halloween looms, the real horror is not in haunted houses but on the southern border, where a resurrected parasite is turning the countryside into a feeding ground for flesh‑eating maggots. The New World Screwworm (NWS), a fly once eradicated from the United States, has breached the nation’s defenses again and is now haunting three states—Texas, New Mexico and, most recently, Arizona. The USDA reports 74 animal cases since the flies slipped back across the Darién Gap in June, and the toll is rising fast enough to demand immediate, coordinated action.

From Eradication to Re‑Invasion: How the Screwworm Came Back

In the 1960s, the United States celebrated the successful elimination of the screwworm through a massive sterile‑male release program that halted breeding. For decades the parasite was held at bay by a biological barrier along the Darién Gap, the dense rainforest frontier between Panama and Colombia. That barrier held until 2022, when it was breached, allowing the flies to travel north through Central America and re‑enter the United States.

The re‑invasion underscores a sobering reality: once‑stable bio‑security measures can crumble, and the fallout is swift. The flies’ life cycle—laying hundreds of eggs in wounds or moist orifices—means that any breach can seed a new wave of infestations across livestock, wildlife and even companion animals.

What the Screwworm Looks Like and How It Kills

The screwworm’s larvae are not just ordinary maggots. They are shaped like tiny screws, twisting and boring into living flesh. Once the eggs hatch, the voracious maggots feed on the host’s tissue, creating deep, tortuous wounds that can become fatal if left untreated. After feeding, the larvae drop to the ground to pupate and emerge as adult flies, ready to repeat the cycle.

This gruesome feeding habit explains why the parasite is such a menace to livestock. A single infestation can devastate a herd, and the same threat now extends to pets and wildlife. The USDA’s recent reports of four new dog cases in Arizona and a cat case in New Mexico illustrate how quickly the threat can spread beyond farms.

Scope of the Outbreak: Numbers and Geography

Since the June re‑entry, the United States has logged 74 confirmed animal cases. The majority involve livestock, but a growing subset involves domestic pets. To date, ten pets—nine dogs and one cat—have been confirmed with screwworm infestations. The latest Arizona case, identified in Cochise County, marks the state’s first confirmed pet infection and expands the geographic footprint of the outbreak.

Beyond the borders of the United States, Mexico’s Ministry of Health reports 806 human cases since the flies re‑emerged, with nine fatalities. While human infections remain rare, the Mexican data highlight the parasite’s capacity for severe outcomes and serve as a stark warning for U.S. health officials.

Impact on Livestock and the Agricultural Economy

Livestock remains the primary target of the screwworm, and the economic implications are significant. The flies’ ability to ravage cattle, sheep and other farm animals threatens the profitability of ranches across the affected states. Even a single infected animal can require costly veterinary care, extensive wound management, and in worst‑case scenarios, loss of the animal.

Farmers in Texas and New Mexico have already been on high alert, and the Arizona Department of Agriculture’s swift announcement signals that the state is preparing for a similar response. Vigilance and rapid reporting are essential to contain the spread before it inflicts broader economic damage.

Pet Owners: What to Watch For and How to Respond

Pet owners in the three affected states should inspect their animals daily for any unusual wounds, especially around the back, neck and any moist areas. The Arizona case involved a dog with a heavily infested wound on its back, a classic presentation of NWS larvae. If a wound appears to be festering with maggots or emits a foul odor, contact a veterinarian immediately.

State agencies urge owners to report suspicious cases without delay. Early detection can mean the difference between a treatable infestation and a fatal outcome. The USDA’s partnership with Arizona on a joint response underscores the importance of coordinated reporting and treatment protocols.

Government and Veterinary Response: Coordination Across Agencies

The USDA confirmed the Arizona infection and is working closely with the state’s agriculture department on a joint response. This collaboration mirrors earlier efforts in Texas and New Mexico, where state and federal agencies have been monitoring and responding to cases. The emphasis is on rapid identification, treatment, and containment.

Veterinary professionals are also on the front lines, as illustrated by the Cochise County veterinarian who identified the maggot‑laden wound on October 26. Their role in early detection is critical, and ongoing training and communication between vets and public health officials will be essential to stay ahead of the parasite’s spread.

Looking Ahead: Preventive Measures and Long‑Term Outlook

While the immediate priority is containment, the longer‑term strategy must revisit the sterile‑male release program that once eradicated the screwworm. Restoring a robust biological barrier, perhaps through renewed sterile‑fly releases or other innovative bio‑control methods, could re‑establish the defensive line that was lost in 2022.

In the meantime, public awareness and vigilance remain the strongest tools. As the screwworm expands its reach, every farmer, pet owner and wildlife caretaker must act as a sentinel. The stakes are high: unchecked, the parasite could inflict a new wave of livestock losses, threaten pet health and, in rare cases, endanger human lives. The fight against the screwworm is just beginning, and the nation’s response will determine whether this horror story ends with a swift containment or spirals into a prolonged agricultural crisis.

This article was produced with AI-assisted research and editorial support. Reporting is based on the source material cited below. Sources: Ars Technica; arstechnica.com; Global1.News (02 November 2026).

By Jessica Ali, Staff Writer