On June 3, 2026, the USDA confirmed the detection of New World Screwworm (NWS) on a cattle ranch near La Pryor, Texas in a 3-week-old bovine’s umbilical incision—the first in livestock since 21966. This detection has large implications and marks the beginning of many agendas against NWS. Naturally, we have taken to Google, to voice our concerns via question and search engine. Take a look below at the most common NWS questions and answers.
What is New World Screwworm?
It’s not a worm. It’s just a strange name for a fly. New World Screwworm (NWS) is a parasitic fly whose larvae require living tissue to feed. NWS is an infestation and a pest problem. It’s not a systemic disease nor a threat to the safety of beef. It’s a pest we are trying to control, not a consumer safety problem.
I thought we eradicated NWS?
Yes, in 1966 NWS was eradicated from the United States. This was accomplished through the release of sterile flies. Since then, occasional outbreaks in wildlife and pets have been quickly eradicated. Unfortunately, just because NWS was eradicated from the U.S. in 1966 does not mean that it didn’t exist elsewhere.
Where is it now?
In South America and some Caribbean countries NWS is endemic, meaning it’s consistently been circulating in those regions. Starting in 2023, it spread through Central America and Mexico. As of currently* there have been 3 cases reported in cattle and one case in a dog in Texas, for the United States.
How does NWS spread?
NWS is not contagious like a virus; it spreads via flies. Females lay eggs in open wounds. In the next 12-24 hours these eggs hatch into larvae that burrow into the living flesh and feed on it. The mature larvae drop to the ground and these adult flies emerge, with the ability to travel miles looking for new hosts. Additionally, this can spread via animal transport of infected animals. Eventually, cold temperatures and hard freezes will suppress (but not eliminate) NWS, as it does not tolerate cold well.
What does it look like?
The adult fly is the same size as a housefly, but with a metallic blue and green body. The larvae are a cream white maggot. On infected animals, you will see maggots inside wounds or wounds that are enlarging instead of healing.
How does it affect my cattle?
The larvae eat living tissue, not dead tissue which can cause pain, enlarging wounds, and secondary infections. Without treatment animals can die in 1-2 weeks. Cattle with injuries or post-processing (castration, dehorning, and branding) are at most risk.
Does it affect other livestock?
Yes, anything that is warm-blooded could be at risk for NWS. This includes all livestock, horses, pets, wildlife and birds.
Is it zoonotic? Can humans get it? Can humans die?
Since NWS is not a disease, it’s not a zoonotic disease concern. Humans can be infested; however, this is very rare. Infection would present as a painful wound that can be easily treated. The risk of death in humans is extremely low, especially if they seek treatment.
What Am I Supposed to Do as a Cattle Producer?
OBSERVE. OBSERVE. OBSERVE. There is no substitute for eyes on cattle. You must inspect animals frequently to identify wounds. You should treat any wound quickly with insecticide and monitor closely. Fly control, now more than ever is essential. Minimizing wounds and careful management at calving, castration and dehorning is key. When possible, move or plan to carry out these practices in colder temperatures. Finally, avoid unnecessary animal movement from risk areas across the country.
Is Illinois going to get it?
NWS is in the United States, but it is not in Illinois. Over time the risk for Illinois could increase, but the USDA is actively trying to stop it before it moves north, so for now it is low. For the Illinois producer, their highest chance of spotting NWS is on animals sourced and transported from infected regions. Awareness is the first step. Staying updated in the news, knowing where NWS has been detected, and learning about the pest itself, are practical steps Illinois cattlemen can take.
How is NWS controlled?
The primary tool to push NWS out of the United States again will be through releasing millions of sterile male flies. A new facility was recently funded by the USDA to produce sterile flies in South Texas and increase the number of sterile flies available. Females only mate once and if they mate with sterile males, the population will collapse over time. Other measures include quarantines, controls on movement, and border controls. If you see or even suspect NWS, say something. Early detection is the number one tool. Not to mention, the faster cases are reported, the faster they can be responded to.
Conclusion
I was sitting at the Illinois Beef Association Annual Meeting listening to guest speaker Colin Woodall, the CEO of the National Cattlemen’s Beef Association, on June 2, 2026. He had a lot to say about the beef industry, but I knew he meant every word when he said, “We’re going to win the battle [against NWS].” At that time, NWS had only been detected 25 miles away from the U.S. border, the question wasn’t will we get NWS. In fact, it never had been. “No doubt, it will be a challenge. No doubt, the market will be ugly… It is not a time to panic,” says Woodall. The USDA, FDA, Congress, and America’s cattlemen have been preparing for the moment NWS entered the United States, developing protocols for moving cattle, options for treatment, and the increase in our supply of sterile flies. It is not a time to panic, because it is time to go into action, working together to combat the spread of misinformation and provide the best care for our cattle.
*This blog was last updated at 3 p.m. on June 8, 2026. For more recent information, visit the USDA's Animal and Plant Health Inspection Service or https://www.aphis.usda.gov/animals/animal-health/livestock-and-poultry-disease/current-status.
Olivia Shike is a student who works in beef production, research, and producer outreach as a University of Illinois Extension intern in the I-BELIEF program through the Department of Animal Sciences in the College of Agricultural, Consumer and Environmental Sciences. This article has been reviewed by Extension Beef Cattle Specialist, Travis Meteer.