Flesh-Eating Screwworm Returns to the USA: What You Need to Know About the Threat to Cattle, Beef Prices, and Humans

Flesh-Eating Screwworm Is Back in the USA: A Growing Threat to Livestock, Beef Prices, and Human Health

A parasitic nightmare that was once eradicated from the United States has returned. U.S. officials have confirmed the detection of the New World screwworm (NWS) within American borders, sending alarm bells ringing across the agricultural industry, beef markets, and public health agencies alike. If left unchecked, this flesh-eating parasite has the potential to devastate cattle populations, trigger significant spikes in beef prices, and even pose a direct risk to human health.

Here is a comprehensive breakdown of everything you need to know about the New World screwworm — what it is, why it matters, and what is being done to stop it.

What Is the New World Screwworm?

Despite its somewhat misleading name, the New World screwworm is not a worm at all. It is a species of parasitic fly scientifically known as Cochliomyia hominivorax, which translates roughly to "human eater." The fly itself is not the primary threat — the real danger lies in its larvae.

Female screwworm flies lay their eggs in the open wounds or natural body openings of warm-blooded animals. These openings include mouths, nostrils, eyes, ears, and genitalia, as well as any cuts, scratches, or injuries on the skin. Once the eggs hatch, the larvae — commonly referred to as maggots — begin to feed on the living tissue of the host animal.

The name "screwworm" comes from the distinctive screw-like shape of these larvae. This shape allows them to burrow deeper and deeper into the flesh in a cork-screw motion, making them extremely difficult to remove and causing escalating tissue damage with every passing hour. Unlike many fly species whose larvae feed only on dead or decaying tissue, screwworm larvae specifically target and consume living flesh, which is what makes them so uniquely destructive and dangerous.

How Was It Detected in the United States?

The U.S. Department of Agriculture's Animal and Plant Health Inspection Service (APHIS) officially confirmed the presence of the New World screwworm in the United States following growing concerns from Texas farmers and the broader American cattle industry. The detection validated what many agricultural experts had been warning about for some time: that the screwworm, which had been eradicated from the continental United States decades ago, was creeping back northward through Central America and Mexico.

The reemergence of screwworm cases in Mexico and neighboring countries in recent years had placed U.S. border states on high alert. Texas, given its vast cattle ranching industry and long shared border with Mexico, was always considered the most vulnerable point of entry. The USDA's confirmation has now made that fear a reality.

Why Is the Screwworm So Dangerous to Cattle and Livestock?

For the American cattle industry, the New World screwworm represents one of the most serious agricultural biosecurity threats in recent memory. The parasite is capable of killing a healthy animal within days if an infestation goes undetected or untreated. In a large herd environment, the fly can spread rapidly from animal to animal, causing widespread infestations that overwhelm ranchers' ability to respond in time.

The economic consequences of an uncontrolled screwworm outbreak would be staggering. The United States cattle industry is one of the largest in the world, supporting millions of livelihoods and underpinning a significant portion of the national food supply. A serious outbreak could lead to:

• Mass livestock deaths across affected regions, particularly in Texas, Florida, and other Southern states
• Significant reductions in the cattle population available for beef production
• Disruption to supply chains that connect ranchers, processors, and retailers
• Sharp increases in beef prices at the consumer level, adding further pressure to already inflation-strained grocery bills
• Long-term damage to U.S. export competitiveness in global beef markets

Historically, screwworm outbreaks in the mid-20th century caused hundreds of millions of dollars in agricultural losses annually before a landmark eradication program — involving the mass release of sterile male flies — successfully eliminated the pest from the United States in the 1960s. Reestablishing that kind of control today would be a costly and time-consuming process.

Can Screwworms Infect Humans?

Yes — and this is a detail that often surprises people. While the New World screwworm primarily targets livestock and wild animals, it is entirely capable of infesting humans. The fly's scientific name, hominivorax, literally reflects this capacity. Any open wound, surgical incision, or even a minor skin break can serve as an entry point for screwworm eggs if a person is exposed to the fly in an infested area.

Human screwworm infestations, known medically as myiasis, have been documented in parts of Central and South America where the parasite is still endemic. Symptoms include intense pain, visible movement beneath the skin, swelling, and secondary bacterial infections. Without prompt medical treatment, infestations can cause serious tissue damage and in extreme cases can be life-threatening, particularly in vulnerable individuals such as the elderly, young children, or those who are immunocompromised.

What Is Being Done to Stop the Spread?

Following APHIS's confirmation, federal and state agricultural agencies have moved quickly to implement surveillance and containment measures. Key response strategies include intensified border inspections of livestock crossing from Mexico, increased monitoring of cattle herds in border states, and rapid deployment of veterinary response teams to affected areas.

There are also renewed discussions about reinstating or expanding the Sterile Insect Technique (SIT) program — the same biological control method that eradicated the screwworm from the U.S. in the 1960s. This technique involves breeding and releasing large numbers of sterile male flies into the environment. When sterile males mate with wild females, no viable eggs are produced, gradually collapsing the wild population over successive generations.

International cooperation, particularly with Mexican agricultural authorities, is considered essential to any long-term containment strategy. Since the screwworm does not respect national borders, a coordinated binational response will be critical in preventing the parasite from establishing a permanent foothold in the Southern United States.

What Should Cattle Owners and the Public Do Right Now?

Ranchers and livestock owners in potentially affected states should be conducting regular inspections of their animals for signs of screwworm infestation, including unusual wound behavior, foul odors, and visible maggot activity. Any suspected cases should be reported immediately to local USDA APHIS offices or state veterinary authorities.

For the general public, awareness is the most important tool. While the risk to urban residents is low, individuals who work outdoors, handle animals, or travel to regions where the screwworm is active should take precautions to keep wounds clean and covered.

The Bottom Line

The return of the New World screwworm to the United States is a serious agricultural and public health development that demands swift, coordinated action. With beef prices already a sensitive consumer issue and the cattle industry facing mounting pressures, the stakes could not be higher. Monitoring the situation closely and supporting robust federal and state response efforts will be critical in the weeks and months ahead.