Your Risk Profile

The New World screwworm isn't actually a worm — it's a fly, Cochliomyia hominivorax, that turns a simple cut into a life-threatening crisis for livestock. The female fly finds an open wound — a nick from barbed wire, a birthing wound, an ear tag site — and lays hundreds of eggs. Within 12 to 24 hours, the hatched larvae begin feeding on living tissue, burrowing deeper as they grow. Untreated, the infestation can kill a mature cow within days.

Before the USDA launched its sterile male fly program in the 1950s, the screwworm caused hundreds of millions of dollars in livestock losses across the American South every year. By 1966, it was gone from the continental U.S. — a triumph of agricultural science. But the program never stopped, because stopping it meant the fly could come back. Now, after the pest broke through its Panama containment zone in late 2024, it has.

How the Screwworm Came Back

• 1966 — Screwworm declared eradicated from the continental United States after a decades-long sterile fly release program
• 1991 — Eradication extended through Central America and into Panama — a biological barrier maintained ever since
• Late 2024 — USDA detects screwworm in Mexico for the first time in decades — the containment line in Panama has broken
• Early 2025 — USDA and U.S. cattle industry launch emergency response — sterile fly production ramped up at facilities outside the U.S.
• June 2025 — Week 1 — First U.S. case confirmed: a 3-week-old calf in South Texas. A second case found miles away days later
• June 2025 — Week 2 — Two more cases confirmed: a calf in La Salle County and a dog in Andrews County — hundreds of miles apart. Total: 4 confirmed cases
• Ongoing — USDA Secretary Brooke Rollins briefed at the U.S. Livestock Insects Research Laboratory in Kerrville, Texas. Eradication effort intensifying

That geographic spread — hundreds of miles between confirmed cases — is exactly what makes agricultural officials nervous. The distance between a La Salle County calf and an Andrews County dog isn't a straight line north toward Ohio; it's a signal that the fly's range is already wider than the known cluster points. Flies travel. Animals travel. Cattle trucks travel. The same interstate corridors that move beef from Texas feedlots to Ohio grocery stores are the same routes that could carry an infestation north.

Ohio ranks among the top ten states for beef cattle and is a major hub for livestock transport. The Ohio Department of Agriculture and USDA's Animal and Plant Health Inspection Service are monitoring the situation — but the key line of defense right now is at the producer level, which is why what happens on farms in Brown, Adams, and Highland counties matters right now, not just when the pest arrives.

Screwworm: Texas vs. The Threat to Ohio's Ag Sector

While we address these instances that require immediate attention, we are simultaneously working to eradicate the pest entirely.Dudley Hoskins, USDA Marketing and Regulatory Undersecretary

The USDA's primary weapon is the same one that worked in the 1960s: sterile male flies. Bred in large quantities, these males are released into the wild, where they compete with fertile males for mates. Since female screwworm flies mate only once in their multi-month lives, a mating with a sterile male means no offspring — and over time, the population collapses. It's elegant, chemical-free, and it works. But it requires massive, sustained production. The USDA is now planning a new fly factory in Texas while ramping up production at facilities outside the U.S.

How Much Do You Know About the Screwworm Threat?

Five questions. Find out if your animals — or your neighbors' — are prepared.

The screwworm fly targets which type of animal?

• Only cattle — Not quite. The screwworm will infest any warm-blooded animal — cattle, deer, dogs, cats, horses, and in rare cases, humans. Any open wound is a potential target.
• Any warm-blooded animal with an open wound — Correct. This is what makes it so dangerous — and why pet owners, not just ranchers, need to stay alert.
• Only wild animals — Actually, cattle are the primary economic concern, but domestic pets and wildlife are both vulnerable. The fly doesn't discriminate.
• Only dead or decaying tissue — That's the common blow fly — a distant relative. The screwworm's larvae specifically target LIVING flesh, which is what makes infestations so rapidly fatal.

When was the screwworm last fully eradicated from the continental United States?

• The 1940s — The eradication campaign began in the 1950s, but wasn't complete until 1966. It required releasing billions of sterile male flies over more than a decade.
• The 1960s — Correct — 1966. It was one of the greatest achievements in American agricultural science. A sterile fly release program that took years to work.
• The 1980s — By the 1980s, the program had pushed the containment line deep into Central America. But the U.S. was actually screwworm-free from 1966 onward — until now.
• It was never fully eradicated — It WAS fully eradicated — that's what makes this resurgence alarming. We proved it could be done. But containment in Panama broke down in late 2024.

How does the USDA's primary defense against the screwworm work?

• Spraying pesticides over infested areas — Aerial pesticide programs can help with some agricultural pests, but the screwworm defense relies on biology, not chemicals — which is part of why it's so effective and environmentally clean.
• Releasing sterile male flies that mate with wild females, producing no offspring — Exactly right. Since female screwworms only mate once, a sterile mating ends her reproductive potential entirely. Do this at scale long enough, and the population crashes.
• Vaccinating livestock before fly season — There is no screwworm vaccine — the defense is behavioral (wound inspection, prompt treatment) and biological (the sterile fly program). Daily wound checks on livestock are critical.
• Installing fly traps at state borders — Trapping and monitoring programs do exist and help track spread — but they're surveillance tools, not control. The sterile fly release is the main weapon for actually reducing populations.

The two newest Texas cases were found hundreds of miles apart. Why is that concerning?

• It means more Texas ranchers are being careless — Proximity of cases has nothing to do with rancher behavior. Wide geographic spread suggests natural fly movement OR movement via livestock transport — both of which are hard to control.
• It suggests the infestation may be wider than the confirmed cluster — That's the real fear. Four confirmed cases hundreds of miles apart means there are likely undetected cases in between — and possibly beyond. Detection always lags behind actual spread.
• It means the USDA response is failing — Not necessarily — the USDA is still in the early stages of eradication. But wide case spread does mean the response needs to scale up quickly to stay ahead of the fly's natural range.
• It's not concerning — flies always spread this fast — This spread pattern IS concerning. The fact that cases popped up in counties hundreds of miles apart in quick succession signals that containment will be very challenging.

What should Ohio and Kentucky livestock owners do RIGHT NOW, even with zero local cases confirmed?

• Wait for USDA to issue an official Ohio alert — Waiting for an official alert is reactive — by then, an infestation could already be established. The right move is to be proactive: establish daily wound inspection protocols now.
• Daily wound inspection on all animals, clean open wounds promptly, contact vet if larvae are visible — That's the playbook. The screwworm spreads fast once established. Early detection — within 24 hours of egg-laying — is the difference between treatment and loss. Daily inspection is the standard.
• Move animals indoors permanently until the threat passes — Practical for small operations but not realistic for most cattle producers. Wound inspection and treatment protocols are the recommended approach from USDA and state agriculture departments.
• Nothing — Texas is too far away to worry about — Distance isn't protection. Cattle trucks travel I-75 from Texas to Ohio regularly. The fly can hitch a ride. Ohio producers should be on alert now, not after the first case is confirmed here.

What's True — And What's Overblown

The screwworm is a worm that infests the ground.

Verdict: false

Despite the name, it's actually a fly — Cochliomyia hominivorax. The 'worm' refers to the larva stage, which burrows into living flesh. It has nothing to do with soil.

Only cattle are at risk from screwworm infestation.

Verdict: false

Any warm-blooded animal with an open wound is a potential host — cattle, deer, dogs, horses, and rarely, humans. USDA confirmed one of the four Texas cases was a dog.

The screwworm was completely eradicated from the U.S. in the 1960s.

Verdict: true

Correct. The sterile male fly release program drove the screwworm out of the continental U.S. by 1966. It remained contained at Panama's southern border until 2024.

Once an animal is infested, there's nothing a farmer can do.

Verdict: false

Early detection — within 24 hours — allows for effective treatment. Larvae can be manually removed and wounds treated with anti-parasitic products. Speed is everything.

The screwworm's return to the U.S. could cost the cattle industry hundreds of millions annually.

Verdict: mostly true

Before eradication, losses ran into the hundreds of millions per year. Today's much larger cattle industry would face potentially greater economic damage — but modern detection and the sterile fly program mean a full-scale resurgence is not inevitable.

What Ohio & Kentucky Livestock Owners Should Do Now

1. Inspect All Animals Daily — Check every wound, surgical site, ear tag hole, and birth injury on your animals every single day. Look for unusual movement in wounds — larvae are visible to the naked eye within 12–24 hours of hatching.
2. Treat Open Wounds Immediately — Clean any wound promptly and apply a USDA-recommended wound treatment. Keep wounds covered or treated to reduce attractiveness to egg-laying flies. Consult your vet about protective products.
3. Know What to Look For — Infested wounds show unusual wriggling, foul odor, and visible larvae burrowing deeper into tissue. Animals will show distress, go off feed, and isolate. Don't wait — call your vet if anything looks wrong.
4. Register With Your State Agriculture Department — Ohio producers should contact the Ohio Department of Agriculture. Kentucky producers contact the Kentucky Department of Agriculture. Get on alert lists so you hear about confirmed cases immediately.
5. Scrutinize Incoming Animals — Any cattle or livestock arriving from Texas or the Southwest should be inspected thoroughly before integration with your herd. Request health certificates and inspect all wounds on arrival.
6. Contact OSU Extension or UK Extension — Ohio State University Extension and the University of Kentucky College of Agriculture have livestock specialists who can walk you through current protocols at no cost to farm operators.

Report a Suspected Case or Get Guidance

• Ohio Department of Agriculture — Animal Disease Hotline: Report suspected screwworm cases or request guidance on wound protocols for Ohio livestock producers.
• Kentucky Department of Agriculture: Kentucky producers and pet owners can report concerns and access livestock health resources.
• USDA APHIS — National Screwworm Response: Federal updates on confirmed cases, sterile fly program status, and quarantine zones are updated regularly by the Animal and Plant Health Inspection Service.
• OSU Extension — Livestock Health Resources: Ohio State University Extension offers free producer consultations and county-level livestock health guidance.

The screwworm's reappearance is a reminder that the victories of agricultural science require constant maintenance. The sterile fly program that eliminated this pest from the U.S. never truly stopped — it just moved the battleground south. Panama was the line. When that line broke in 2024, the clock started. Now the USDA is building a new fly factory in Texas, ramping up sterile male production, and briefing cabinet secretaries — all the signs of an agency that knows what a full resurgence would cost.

For Greater Cincinnati's farm families, the answer isn't panic — it's preparation. Brown County, Adams County, Highland County, and the agricultural stretches of Northern Kentucky grow and raise a significant piece of this region's food economy. The ranchers and smallholders who tend those animals are the first line of defense. Daily wound checks don't make headlines. But they're exactly the kind of unglamorous vigilance that kept this pest out of Ohio for sixty years — and the kind that could keep it out for sixty more.

The Science Behind the Sterile Fly Program

The Sterile Insect Technique (SIT) is considered one of the most elegant tools in pest management. It exploits a biological vulnerability unique to the screwworm: females mate only once in their entire lives. By flooding the population with sterile males — flies that have been irradiated to prevent viable sperm — the program ensures a growing percentage of matings produce no offspring.

At peak operation, USDA and partner facilities produced hundreds of millions of sterile male screwworm flies per week, releasing them by aircraft across the eradication zone. Over months and years, wild population density dropped until the pest was functionally extinct in the target area.

The program worked so well that when combined with a biological barrier at Panama's Darien Gap, it was able to keep the entire North American and Central American landmass screwworm-free for decades. The current outbreak in Mexico and Texas represents the first major containment failure since the 1960s. USDA is now planning a dedicated sterile fly production facility in Texas to reduce dependence on facilities outside U.S. borders — a supply chain lesson learned from the pandemic era applied to agriculture.

Sources & References

• Primary source: news — AP via Scripps News Group
• USDA Animal and Plant Health Inspection Service (APHIS) — New World screwworm case confirmations, sterile fly program details, and eradication history
• USDA Agricultural Research Service — Sterile Insect Technique science and historical U.S. eradication program documentation
• Ohio Department of Agriculture — Ohio livestock operation counts, animal disease reporting protocols
• Kentucky Department of Agriculture — Kentucky cattle industry size and livestock health monitoring resources
• Associated Press / Scripps News Group — Original reporting on confirmed Texas screwworm cases, USDA response, and case geography