Introduction | The 2025 Threat of New World Screwworm
October 2025 — Few insect pest threats are as unsettling as the New World Screwworm, an insect whose larvae feed not on decaying matter but on the living tissue of warm-blooded animals. For farmers and ranchers, its recent resurgence in parts of the United States has reignited concerns about animal health, production losses, and food security.
The New World Screwworm (Cochliomyia hominivorax) has a long history of devastating livestock and wildlife. While it was once classified as eradicated from the U.S., recent detections have raised red flags for veterinarians, producers, and regulatory agencies. That’s why we felt it was important to share information on this concerning development in this month’s blog, so agricultural professionals can better understand the pest’s history, the dangers it presents, and why vigilance remains vital.
What is the New World Screwworm?
The New World Screwworm is a parasitic fly whose larvae burrow into open wounds of living animals. Females lay clusters of eggs at wound sites, and within a day, larvae hatch and begin feeding. Unlike other maggots that survive on dead material, screwworm larvae consume healthy tissue.
Its name comes from the screw-like shape of the larvae, which twist deeper into flesh as they grow. Infestations can occur in cattle, sheep, goats, horses, swine, and even pets or wildlife. In severe cases, human infections are possible. Essentially, if a wound exists and the insect is present, the screwworm poses a risk.
History of New World Screwworm in the U.S.
The insect was first identified in the early 20th century and quickly became a leading cause of livestock losses. Before eradication programs began, producers faced hundreds of millions of dollars in damages each year.
From the 1950s through the 1980s, the U.S. Department of Agriculture deployed the Sterile Insect Technique (SIT). This innovative approach released massive numbers of sterile male flies to overwhelm wild populations, reducing reproduction rates until the species was wiped out across the continental U.S. By the early 2000s, screwworm was declared eradicated from the U.S. and most of North and Central America.
That success story, however, does not guarantee permanent safety, as farmers and ranchers are discovering in 2025. Any reintroduction of the pest threatens to undo decades of progress, placing both livestock and food supplies at risk.
Areas in the U.S. Recently Impacted
The New World Screwworm has not disappeared entirely. In 2016, an outbreak in the Florida Keys infected endangered Key deer, requiring rapid intervention to prevent wider spread. More recently, reports near the Texas–Mexico border have drawn attention from ranchers and regulators.
The Gulf Coast and southern border states remain at highest risk due to warm climates and proximity to endemic regions. Surveillance programs continue to operate in these areas to detect and ideally, help contain new introductions before they gain traction. Additionally, the U.S. is building a “sterile fly production facility” in Texas, to provide additional support against this pest.
Why the New World Screwworm is Dangerous
The threat posed by this pest extends beyond individual animals:
Economic consequences: Infestations reduce livestock weight gain, lower milk production, increase veterinary costs, and trigger trade restrictions. Losses can escalate quickly across large herds.
Animal welfare concerns: Larvae cause severe pain, deep wounds, and secondary infections. Untreated animals can die.
Human health risks: While rare, people can become infested, especially in rural or agricultural settings. Symptoms can include painful swelling, fever, oozing wounds, and visible larvae.
Environmental impacts: Wildlife such as deer, antelope, or wild pigs are also susceptible, making outbreaks difficult to contain and harmful to ecosystems.
New World Screwworm in Commercial Agriculture
The sectors most exposed are those relying heavily on livestock, particularly cattle, sheep, goats, and swine. Producers must watch for telltale signs: animals with untreated wounds, foul odors, or visible larvae.
Costs of treatment and monitoring can rise quickly, not only from direct care but also from labor and productivity losses. Regulatory responses may include quarantines or movement restrictions, which add further strain to agricultural operations.
New World Screwworm Detection and Management Strategies
Although detailed management plans are overseen by veterinary and regulatory agencies, producers also play a central role in early detection.
Surveillance and reporting: Regular livestock inspections and immediate communication with veterinarians are key.
Treatment: Infected wounds require prompt cleaning and insecticidal treatment.
Sterile Insect Technique (SIT): This proven approach remains the cornerstone of eradication campaigns.
Integrated pest management (IPM): Combining insect monitoring, farm-level best practices, and coordinated responses can help prevent reintroduction.
On farms, the basics still matter. Inspect animals frequently, treat wounds promptly, and notify authorities of suspected cases. These simple steps can prevent outbreaks from spreading.
Global Perspective of the New World Screwworm
Today, the New World Screwworm remains present in parts of South America and the Caribbean. International livestock movement and human travel pose constant reintroduction risks. For this reason, U.S. agencies maintain active surveillance zones near Mexico and along coastal entry points. Cooperation between nations is essential to control the pest’s geographic range.
New World Screwworm Frequently Asked Questions
What exactly is the New World Screwworm?
It is a parasitic fly whose larvae feed on the living tissue of warm-blooded animals.
How can I tell if my livestock are infested with New World Screwworm?
Look for open wounds that worsen quickly, foul odors, and visible larvae burrowing into tissue.
Is the New World Screwworm dangerous to humans?
Yes, although rare, humans can become infested. Cases typically involve painful swelling and larvae emerging from wounds.
Where in the U.S. has New World Screwworm been detected recently?
Outbreaks have been documented along the Texas–Mexico border.
How was New World Screwworm eradicated in the past, and can it happen again?
The U.S. used the Sterile Insect Technique (SIT), which successfully eradicated the pest. With vigilance, eradication is achievable again.
What should farmers do if they suspect a New World Screwworm on their animals?
Contact a veterinarian immediately and report suspected cases to local agricultural authorities.
The Takeaway | New World Screwworm and Commercial Agriculture
The New World Screwworm represents more than a nuisance. It is a dangerous pest with the ability to inflict severe economic and animal welfare consequences. History shows that eradication is possible, but only through coordinated action and constant monitoring.
Farmers and ranchers can serve as the first line of defense by monitoring herds closely, treating wounds quickly, and reporting concerns without delay. Technology also plays a growing role. Autonomous pest monitoring advancements like FarmSense’s FlightSensor could play a significant role in early detection of New World Screwworm and similar pests, ultimately providing vital data to support eradication initiatives.
Protecting livestock today means remaining alert to threats that were once thought to be in the past. By staying informed and proactive, agricultural communities can help ensure that the New World Screwworm does not regain a foothold in the United States.