Screw Worm or Screw Americans?

What Comes Out of the Egg

The scientific name is Cochliomyia hominivorax. It means man-eater.

Every other fly you have ever cursed at is a scavenger. It wants what is already dead.

This one does not.

The female finds a wound on a living animal and lays two to four hundred eggs at the edge of it. They hatch in ten to twenty-one hours. The larvae go in.

Not into dead tissue. Into the living animal. They feed for five to seven days, screwing deeper as they go, which is where the name comes from.

An untreated animal dies in seven to fourteen days. (Merck Veterinary Manual)

The wound does not have to be much. A tick bite. A branding iron. A castration.

Mostly it is a newborn calf's navel, which is why this parasite has always hit the cow-calf man hardest. He is the one with wet calves on the ground.

In warm country the whole cycle runs in twenty-one days.

Then Two Men From Texas Solved It

Here is the part that should be taught in every school in this country and is taught in almost none.

The female screwworm mates once. One time. Her entire life.

A man named Edward Knipling, raised in Texas, wrote a letter in 1946 asking whether geneticists could make a sterile screwworm fly. Not kill her. Waste her.

Raymond Bushland, who ran the government lab at Kerrville, figured out how to raise the flies by the million and sterilize them with X-rays.

You do not have to kill the fly. You only have to be the one she mates with.

They tried it on Sanibel Island in 1951. Then on Curaçao, forty miles off Venezuela, in 1953.

It worked.

Florida put up state money in 1958 and Washington matched it. They built a plant that made fifty million sterile flies a week and dumped them out of airplanes over the Southeast.

By early 1959 the screwworm was gone from Florida.

Then Texas. Ranchers in the Southwest formed their own foundation and raised over three million dollars of their own money to do it. By 1966 the plant at Mission, Texas was turning out a hundred and fifty million sterile flies a week.

In 1966 the United States Department of Agriculture declared this country free of screwworm. (Texas Tribune)

Not controlled. Free.

The industry saved more than nine hundred million dollars a year, every year, from that point forward.

Knipling and Bushland won the World Food Prize in 1992. The method they invented in a Texas lab is now used against pests on five continents.

Two government scientists and a lot of ranchers who paid out of pocket erased a plague from a continent.

That happened here. That is who we are when we decide to be.

Remember that, because the rest of this is about what we did with it.

The Bill Nobody Mentions

1966 was not the end. It was the beginning of the payment plan.

The fly was still south of us, and a fly does not respect a line on a map.

It came back into Texas in 1976. Producers spent a hundred and thirty-two million dollars fighting it. In today's money that outbreak cost Texas producers and the state economy roughly one-point-eight billion dollars.

So we did not stop. We pushed the line south, through Mexico, over decades, plant by plant.

And then all the way to the bottom of Central America, to a sixty-mile neck of jungle in Panama called the Darién Gap, where the continent pinches almost shut.

In 2006 a plant went up there. A hundred million sterile flies a week, released over the narrowest place in the hemisphere, forever.

The United States paid ninety percent of it.

APHIS estimated in 2025 that this arrangement returns $2.3 billion a year to the American cattle industry. (Congressional Research Service)

Best deal this country ever made in agriculture, and almost nobody in it has ever heard of the place.

We were so confident that we closed our own production plant in Texas in 1982. Did not need it. The fence was a thousand miles south and holding.

For forty years it held.

2023

Panama had twenty-five cases of screwworm.

Then it had more than six thousand five hundred.

The fence broke.

By late 2024 the fly was in southern Mexico. In November of that year the United States closed the border to Mexican cattle.

What happened next is the fact this whole article turns on.

A Fly That Traveled Seven Hundred Miles in Ten Weeks

The Wildlife Conservation Society tracked the parasite from the Nicaragua-Honduras border to Catazajá, Mexico.

Seven hundred miles. About two and a half months. (Wildlife Conservation Society)

No fly does that.

A screwworm does not cross seven hundred miles of Central America in ten weeks under her own power. She was carried.

She was carried on cattle.

Mexico's own animal health agency, SENASICA, estimates that around eight hundred thousand head of cattle a year are trafficked into Mexico from Guatemala. Not imported. Trafficked. No health papers, no traceable identity, moving north out of Nicaragua and Honduras and Guatemala into the Mexican supply chain. (SENASICA estimate, reported by InSight Crime)

In the first six months of 2025, the state of Chiapas alone seized more than half a million non-compliant ear tags.

There is a black market in counterfeit cattle identification. A fake tag runs up to a thousand pesos, about fifty dollars. A real one costs two and a half.

Somebody is paying twenty times the price of a legitimate tag specifically so that an animal cannot be traced.

Jeremy Radachowsky, who runs the Wildlife Conservation Society's Mesoamerica program, put it plainly: the outbreak hotspots track the smuggling routes.

Antonio Ortiz-Mena of Georgetown was blunter. "This is no longer informal smuggling," he said. "It's transnational crime."

The fly did not fly here. It rode.

Eighty-Two Days

The border reopened at one port, Douglas, Arizona, on the twenty-fourth of August, 2026.

The screwworm reached that calf in Zavala County on the third of June.

The parasite beat the reopening by eighty-two days — and it arrived in the middle of a closure that had already been running almost two years.

Read that again.

We shut the legal channel. The inspected one. The one with a federal veterinarian standing at the chute.

And the pathogen walked in anyway, because it was never using the legal channel.

Every animal crossing at Douglas today gets a full USDA veterinary inspection, a radio-frequency ear tag, a scanner reading that tag, and a dog walking the pens. Seven hundred head a day the first week, nine hundred the second, thirteen hundred the third. One detection at that facility and the whole thing shuts. (USDA)

Nobody is doing any of that to the eight hundred thousand.

The animals we can see are the ones we inspect. The animals we cannot see are the ones that brought it.

So Who Got Screwed?

Let us be exact about this, because it is the question in the title and it deserves a real answer.

Not the fly. The fly had two good years. It is now in thirty of Mexico's thirty-two states and it is in Texas.

Not the smuggler. Eight hundred thousand head a year, by Mexico's own estimate, and a fifty-dollar tag that makes an animal disappear. Two years of closure did not cost that trade one animal.

The Mexican rancher in the south got screwed. He watched his herd get eaten alive and lost his only export market in the same season. He has been the loudest voice demanding somebody stop the smuggling, because it is his cattle it destroys first. He is not the problem here. He is the first casualty.

And the American cattleman got screwed twice.

Once on the way in. Feedyards in Arizona, New Mexico and Texas lost the calf supply they were built around for two years, and the pest arrived regardless.

And once on the way out. Which is the part worth slowing down for.

The Second Screwing

Here is where the American herd actually stands.

(USDA July Cattle report, via American Farm Bureau Federation)

Three of those four numbers are bad.

The fourth one is a man standing in a pen in October, looking at a heifer calf worth real money today, and deciding not to sell her.

It is the first genuine sign of rebuilding in years. And it costs him two full years of feed before she gives him a single calf.

Now. On the twenty-seventh of July, when the reopening was announced, deferred feeder cattle futures closed limit down.

The market punished the man who kept her, on the news that a hundred and fifty thousand calves might come north.

And what does the country get for that?

Derrell Peel at Oklahoma State expects roughly a hundred and fifty thousand head to cross for the rest of this year. Against an American calf crop of thirty-two and a half million.

Even at full volume, the twenty-five year average is about 1.15 million head, some 3.3 percent of our calf crop. (Derrell Peel)

And they are calves. Fourteen to twenty-two months from anybody's plate.

"I don't expect to see any measurable impact on cattle prices or beef prices soon," Peel said. (PBS NewsHour)

David Anderson at Texas A&M says the herd shrank over decades of low prices and drought and that rebuilding takes years. Glynn Tonsor at Kansas State says the opening and closing has "added risk and uncertainty to the broader beef cattle marketplace."

Josh Maples at Mississippi State says the quiet part: breeding decisions made now set supply two and three years out. Push the price down today and you push the calf out of existence in 2029.

So the ledger reads: no measurable relief at the meat case, and a price signal aimed straight at the one man who just chose to rebuild the herd.

Ground beef is $6.89 a pound, up 57% in five years. Steak hit a record $13.06 in July.

None of that is coming down because of a hundred and fifty thousand calves.

Nobody Set the Pregnancy, But Somebody Sets the Priorities

I want to be careful here, because it would be easy and popular to point at a person.

No packer invented this fly. No agency wanted it back. Nobody in Washington decided a screwworm should eat a calf in Zavala County.

The biology is nobody's fault.

But where the bill lands is not biology. That part is a choice, made every time.

We chose to build the plant in 1958 and we chose to close it in 1982.

We chose to pay ninety percent of the Darién Gap for twenty years, and we chose not to notice when it started failing in 2023.

We chose to close the inspected channel for two years, and we chose not to do anything about the uninspected one.

Reasonable people are still arguing about the last one. R-CALF says keep the border shut until the pest is eradicated. NCBA says the protocols are good enough to open safely. Both of those groups have cattle on the ground and both are arguing in good faith.

But notice what neither argument can fix. Whether Douglas is open or closed changes nothing about eight hundred thousand untagged animals a year entering the system a thousand miles south.

We are also, right now, spending seven hundred and fifty million dollars at Moore Air Base in Texas to build a plant making three hundred million sterile flies a week — twice what Mission, Texas made in 1966. Plus a dispersal facility finished this February and a production plant at Metapa in Chiapas opened in June. (USDA APHIS)

Which is the right thing to do.

It is also three quarters of a billion dollars to replace a capability we already had and shut down because we thought we had won.

Raised in America

People hear a phrase like that and assume it is about keeping something out.

It is not. It never was.

It is about being able to answer a question.

Where did this animal come from, and who is willing to put his name on the answer?

Everything in this article turns on that one question.

The fly did not beat American science. American science beat it in 1966 and beat it so thoroughly that we forgot it existed.

What failed was the paperwork. A tag you can buy for fifty dollars. Eight hundred thousand animals a year entering a supply chain with no name attached to them.

A traceability system is worth exactly as much as the weakest point where an animal enters it. Everything downstream — the veterinarian at Douglas, the scanner, the dog, the federal grade stamp — is only as honest as that first entry.

And here is the thing that ought to make you angry on his behalf.

The American rancher already has the answer. He knows which pasture, which cow, which year, which calf. He has known it his entire life and so did his father.

He has just never had anywhere to say it.

He sells into a system that strips his name off the animal at the first gate and hands the value of that name to somebody else.

Nobody smuggles an animal into a system where the producer's name is on the box.

That is the whole idea. Not a slogan about a flag. A name, on a product, attached to a place, that a stranger can check.

Raised in America is a claim about accountability. And the reason it matters is that this year we all watched, in real time, what happens when nobody can make one.

One Thing I Am Not Going to Do

I am not going to scare you about your dinner.

There have been zero locally acquired human cases of screwworm in the United States. One case in 2025, in a traveler returning from El Salvador. The CDC's assessment is that the risk to the public is very low. (CDC)

This is not a food safety story, and anybody selling it to you as one is selling you something.

It is the story of a country that did something extraordinary sixty years ago, paid quietly to protect it for six decades, let it lapse, and then handed the bill to the last people who could afford it.

The screwworm is going to get beaten again. We know how. We invented how.

The other thing — the part where the American cattleman eats every closure, every reopening, every futures limit-down, and still cannot put his own name on his own animal —

that one we can fix without a laboratory.

We just have to let the man who raised her say so.