Flesh-Eating Screwworms Have Arrived in Texas and New Mexico
Five confirmed cases of the New World screwworm have been found in the United States as of June 9 — three new ones announced Monday bringing the total to five in under a week. The parasite, which was eradicated from the US in the 1960s, has been creeping northward through Central America and Mexico since 2023 and has now officially crossed the border.
Texas Governor Greg Abbott declared a state of disaster on June 5. Canada responded by banning Texas livestock imports entirely. Texas officials called the Canadian response an overreaction. The beef industry is watching nervously.
A widespread outbreak could cost Texas alone $1.8 billion in economic damage and push beef prices even higher — which matters because beef has already been climbing steadily since December 2020, driven by strong demand and the smallest US cattle herd in 75 years.
Where the Cases Are
The five confirmed locations are two calves in Zavala County Texas, one calf in La Salle County Texas, one goat in Gillespie County Texas, and one dog in Lea County New Mexico. The cases are scattered across south and central Texas and into New Mexico — a geographic spread that suggests the infestation isn't contained to one entry point.
What This Parasite Actually Does
The New World screwworm is one of the more disturbing parasites in existence. The flies — roughly the size of common houseflies — lay their eggs in open wounds on living warm-blooded animals. A wound as small as a tick bite is enough to attract them. The eggs hatch into larvae that burrow into the living flesh using what the USDA describes as "sharp mouth hooks" — feeding not on dead tissue like most maggots but on living flesh. The process is extraordinarily painful and often fatal if untreated.
After feeding the larvae drop to the ground, burrow in, and later emerge as adult flies ready to repeat the cycle. The infection — called myiasis — can affect livestock, wildlife, birds, pets, and in rare cases humans. It does not infect meat or fruit, so the food supply itself isn't directly contaminated — but infected cattle don't thrive, don't gain weight, and often die, which is why the economic threat to beef production is serious.
The parasite is native to South America and the Caribbean. The US eradicated it in the 1960s through a massive decades-long program of releasing sterile flies — males that compete with fertile males for mating but produce no offspring, gradually collapsing the population. Mexico was cleared by the 1970s and most of Central America by the early 2000s.
Then in October 2024 new cases appeared in Panama, Costa Rica, Nicaragua, and Honduras. By November the first case in southern Mexico was reported. The northward march toward the US border had begun again.
What Human Infection Looks Like
Cases in humans are rare but they happen and they are not subtle. Symptoms include skin lesions that don't heal and get worse over time, painful open sores, bleeding wounds, a foul smell from the infection site, and — in the most severe cases — the sensation of larvae moving inside a wound, nose, mouth, or eyes.
Secondary bacterial infections can develop causing fever and chills. If you suspect an infestation the CDC is clear — do not try to remove maggots yourself. Get to a medical professional immediately.
What's Being Done
The USDA is deploying the same sterile fly strategy that worked in the 20th century, just at much larger scale and faster pace.
Currently 100 million sterile flies a week are being brought in from a facility in Panama and dispersed in and around affected areas in Mexico. A $21 million facility modernization in Metapa, Mexico is expected to open this summer and will produce 60 to 100 million sterile flies weekly. A $750 million sterile fly production facility under construction at Moore Air Base in Edinburg, Texas will have a projected capacity of 300 million sterile flies a week when it opens in November 2027.
The strategy works — it's been proven before. The challenge is speed. The screwworm is already in Texas and New Mexico. Whether the sterile fly releases can get ahead of the spread before it reaches significant livestock populations is the question ranchers and USDA officials are racing to answer.
Five cases confirmed. More likely coming. The last time this parasite was in the United States it took decades and enormous resources to push it out. The hope is that this time the response is faster than the fly.
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