06/25/2026
Every Oklahoma Rancher and Hunter Needs to Know About the New World Screwworm
For decades, most Americans never had to think about the New World screwworm because it had been eradicated from the United States. Unfortunately, it’s back on everyone’s radar.
This isn’t just another fly.
The New World screwworm is one of the few parasites in the world whose larvae feed on living flesh. A female fly can lay hundreds of eggs in something as small as a tick bite, a branding wound, an ear tag hole, a cut from barbed wire, a fresh castration site, or any other open wound. Within hours, the larvae hatch and begin burrowing deeper into healthy tissue.
Unlike ordinary maggots that feed on dead tissue, screwworm larvae actually consume living tissue. Left untreated, the wound grows larger, attracts even more flies, and can quickly become life-threatening.
Why ranchers should care
A widespread outbreak could have major consequences for the livestock industry.
• Increased calf losses
• Reduced weight gain
• Expensive veterinary treatment
• More labor checking livestock
• Greater risk to newborn calves
• Delays in branding and processing
• Significant financial losses
Every rancher knows that healthy cattle start with daily observation. During periods of increased risk, it becomes even more important to inspect animals frequently, especially after branding, tagging, castration, calving, dehorning, predator encounters, or fence injuries.
Why hunters should care
This isn’t only a cattle issue.
White-tailed deer, elk, feral hogs, bears, and many other wildlife species can also become infected. Wounds from fighting during the rut, predator attacks, fence crossings, or non-fatal hunting injuries can all become sites where screwworm flies lay eggs.
That means this parasite has the potential to impact wildlife populations just as much as livestock.
As hunters and land managers, we all have an interest in maintaining healthy wildlife herds.
Prevention starts with good management
While no one can eliminate all risk, there are practical steps that greatly reduce the chances of infestation.
• Check livestock regularly during fly season.
• Treat cuts and surgical wounds promptly.
• Use veterinarian-approved wound sprays and fly control products.
• Minimize unnecessary handling during periods of heavy fly activity.
• Watch newborn calves closely.
• Report suspicious cases immediately to your veterinarian or state animal health officials.
Early detection is one of the best defenses we have.
Can it be eliminated again?
The encouraging news is yes.
The same technology that eradicated screwworm from the United States decades ago is once again being used today.
Scientists raise millions of sterile male screwworm flies and release them into affected areas. Female screwworm flies mate only once in their lifetime. When they mate with a sterile male, no offspring are produced. Releasing enough sterile males causes the wild population to collapse over time.
It sounds almost too simple, but it remains one of the most successful biological control programs ever developed and was responsible for eliminating screwworm from the United States in the last century.
Today, USDA, state agencies, Mexico, and international partners are once again using this strategy while increasing surveillance, quarantines, and sterile fly production to stop the parasite before it becomes established across North America.
As someone who spends a lot of time on ranches and in the outdoors, I believe this is something every rural landowner should be aware of. Staying informed, checking livestock and wildlife carefully, and reporting suspicious cases quickly can make a tremendous difference.
Healthy cattle. Healthy wildlife. Healthy rural communities.
That’s something worth protecting.
