The Parasite That’s Getting Dangerously Close to the US

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A fly capable of laying hundreds of eggs inside living flesh is heading our way. Known as the New World screwworm, reports suggest that this terrifying parasite is now only 90 miles from the state of Texas.

In less than a year, the screwworm has traveled a great deal; last July, the closest confirmed case was detected approximately 370 miles south of the U.S.-Mexico border. By September, a single infection turned up about 70 miles from the Texas border in Sabinas Hidalgo, Nuevo León, and now, this April,  the Texas Department of Agriculture confirmed detections roughly 90 miles from the border , which is the closest the parasite has come to the U.S. since it was eradicated here in 1966.

Texas Agriculture Commissioner Sid Miller has called this parasite an imminent threat, alongside the USDA. What is the New World screwworm, and what might happen if it arrives on U.S. soil? Is it only a matter of time, or can something be done to stop it? Here’s everything you need to know about this parasite, including its chances of wreaking havoc on the agriculture industry.

What is the New World Screwworm?

The New World screwworm ( Cochliomyia hominivorax ) is different from most parasites, simply because it only targets living animals. Female flies, though not parasites themselves, effectively begin the parasitic process by laying batches of 200 to 300 eggs in open wounds and natural orifices, such as nostrils, ears, eyes, and mouths.

When the eggs hatch, the larvae burrow inward and feed on the living flesh of their host, widening the existing wound and screwing in deeper (hence their horrifying name). With each molt, they secrete substances that attract more females to lay more eggs in the same site, which means that any untreated infestations are almost always fatal. It’s next to impossible to stop this parasite once it begins its gruesome ambush.

Any wound can attract the screwworm, and livestock in warm climates in particular carry dozens of vulnerabilities every single day. This is part of what makes the screwworm so difficult to contain once it establishes a foothold in a region.  As University of Bristol entomologist Richard Wall explained in a recent analysis , the parasite’s devastation is real and possible: in 1935, a single epidemic in Texas produced approximately 230,000 livestock cases and 55 human cases in one state alone, making it a risk that modern experts can’t ignore.

How the Screwworm Arrived in Mexico

The screwworm’s arrival in Mexico wasn’t expected, as its eradication was supposedly previously achieved back in the 1960s through the sterile insect technique, or SIT. This involved mass-producing male flies that were sterilized with radiation and released into the wild. For decades, a facility in Panama maintained the sterile fly population to prevent the screwworm parasite from spreading north. So, what changed this and put both Mexico and the U.S. potentially at risk?

Rearing facilities for sterile insects in Mexico were shut down after eradication, and funding and monitoring challenges in 2025 contributed to the parasite’s spread. Without funding and the experts needed to monitor a potential outbreak, the movement of infected cattle across Mexican states allowed the parasite to spread much faster than predicted.

Climate is also a key factor, with warmer temperatures extending the screwworm’s possible habitat range further north. Warmer weather also shortens its reproductive cycle, meaning flies develop and spread faster in these warmer regions. As locations heat up, there are far more areas for the screwworm to spread, with little to no funding available to stop it.

What Happens if This Parasite Takes Over?

According to estimates made by Senator John Cornyn , a screwworm outbreak could cost Texas livestock producers between approximately $732 million to $1 billion, given that Texas is the single largest cattle-producing state in the country. Agricultural groups predict a potential total national economic loss exceeding $10.6 billion in the event of a screwworm outbreak.

It’s important to note that cattle aren’t the only animal at risk.  According to USDA experts , any warm-blooded creature is a potential host, including pigs , dogs, deer , birds, and in rare cases, humans. In fact, the U.S. confirmed its first human case of the screwworm parasite in August 2025, in a person who had returned from El Salvador. With so many potential hosts and a warming world, what can be done to stop the screwworm before it gets out of hand?

Possible Solutions for the New World Screwworm

Experts already have a tried-and-true option to stop the screwworm: the sterile insect technique.  According to the American Veterinary Medical Association , a sterile fly dispersal facility at Moore Air Base in Edinburg, Texas was completed in February 2026, and a new production facility broke ground in April 2026, expected to begin producing 100 million sterile flies per week by July 2026. The USDA is also collaborating with Mexico to support sterile fly production and screwworm control efforts.

In January 2026, the USDA launched the New World Screwworm Grand Challenge, a $100 million initiative designed to fund new detection tools, improved traps and lures, advanced therapeutics, and next-generation screwworm control technology. The FDA has also issued emergency use authorizations for several animal drugs to be used in the event of confirmed infestations.

Will these efforts be enough to keep the screwworm out of the U.S.?

The Potential Future of This Parasite

The U.S.-Mexico border has been closed to cattle and livestock imports from Mexico since May 2025, causing Mexican cattle exports to drop by 78% in 2025, totaling $335 million. The U.S. imported about 1.2 million head of Mexican cattle in 2024. Meanwhile, the USDA and Mexican authorities are jointly monitoring nearly 8,000 traps across southernmost states, with no screwworm flies detected north of the border as of this article.

The challenge that remains is, unfortunately, political, as well as financial. The real question surrounding the potential future of the New World screwworm is whether the United States is building its defenses faster than the fly is moving north.

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