What to know about flesh-eating screwworms (and why you don’t need to panic)

This article originally appeared on PolitiFact.

A deadly flesh-eating parasitic larva was just found in a human in the U.S. Is that cause for panic?

Probably not. State and federal health officials say that the public health risk from this travel-related case is low. The nasty bugger known as the screwworm has been largely eradicated in the U.S. since the 1960s, and human cases aren’t common. Even in places where screwworms are more prevalent, they mostly infect livestock.

READ MORE: Person in U.S. diagnosed with flesh-eating screwworm after travel to El Salvador

But an outbreak in Central America and Mexico, where they were previously eradicated, has prompted the U.S. Department of Agriculture and Texas officials to take precautions in case of an incursion across the U.S. southern border. Luckily, scientists have well-developed methods of containment and eradication.

Here’s what you should know about the New World screwworm.

Fair warning: This gets unpleasantly graphic.

What is a screwworm?

The adult screwworm is actually a fly, but it’s most dangerous in its larval stage. Flies lay their eggs in the fresh wounds or orifices of warm-blooded animals — it mostly affects livestock but can happen in pets or humans.

A wound as small as a tickbite can attract an adult female fly, which can lay 200 to 300 eggs at a time.

READ MORE: 7 reasons flesh-eating screwworms are as gross as you think

When the eggs hatch after a day or so, the larvae burrow into the skin like a screw (giving it its name) and begin to eat the flesh. Existing infections will often attract more flies to lay eggs, causing the infections to grow. After five to seven days, mature larvae will fall off and burrow into the ground to finish growing into flies. Left untreated, the worms can seriously damage tissue and even result in death.

An Iowa State’s Center for Food Security and Public Health fact sheet sheds light on more details about the squirmy worms that could be hard to read.

How did it get here and who is at risk?

The Centers for Disease Control and Prevention confirmed Aug. 4 that a Maryland resident who had recently returned from El Salvador was treated for screwworm, according to Health and Human Services spokesperson Andrew Nixon.

Maryland Department of Health spokesperson David McCallister told PolitiFact that the patient had recovered and “the investigation confirmed there is no indication of transmission to any other individuals or animals.”

An Aug. 26 Health and Human Services Department press release stated that the USDA “initiated targeted surveillance” for the New World screwworm within a 20-mile radius around the “affected area” including parts of Maryland, D.C., and Virginia. “To date, all trap results have been negative” for screwworm, the release stated.

READ MORE: Flesh-eating screwworms return to U.S.

The infestation comes from insects, not other people, so it is not infectious like a virus or bacteria. The worms in the infection would have to mature, fall off, mate and lay more eggs in order to infect someone else.

Nixon said that the risk to U.S. public health from this case was “very low.”

Carlos Mahr, cattle producer and president of the Chiapas Livestock Union, sprays disinfectant on one of his cows as the Mexican government and ranchers struggle to control the spread of the flesh-eating screwworm, in Tuxtla Gutierrez, Chiapas state, Mexico, July 3, 2025. File photo by Daniel Becerril/Reuters

Screwworms don’t differentiate between humans and other mammals, although human infections are rare. “We are a source of a wound, and that’s where they’re going to drop their eggs,” said Phillip Kaufman, a Texas A&M University entomology professor.

Since an outbreak was declared in Central America in July 2023, the Commission for the Eradication and Prevention of Screwworm said it tracked more than 49,500 cases as of July 12. The Commission’s breakdown of infections by species said that 161 cases were in humans. The vast majority, 85%, were in bovines including cattle, bison and water buffalo, with most of the rest of the cases in other non-human animals.

WATCH: Agriculture Secretary Rollins and Texas Gov. Abbott discuss plans to fight screwworm parasite

The flies are mostly found in South America and the Caribbean, but since the 2023 outbreak, health officials have identified more cases in Central America and Mexico. According to the CDC, people traveling to regions where the flies are present are most at risk if they have open wounds, sleep outside or are around livestock. Covering up wounds can help prevent infection.

Anyone who believes they may be infected should seek medical attention immediately. Kaufman also advised keeping an eye on pets. If they are licking the same spot repeatedly or behaving strangely, make sure there are no wounds infected with larvae.

U.S. and state officials are working to address outbreak in Central America and Mexico

If this is the first time you are hearing about screwworm, that’s largely because U.S. and Central American countries have worked together for decades to create a biological barrier in Panama’s Darién Gap and prevent the flies’ northward incursion. The effort involved releasing sterilized flies into the environment that mate but do not produce eggs.

That work led to screwworms being largely eliminated in the region, with the exception of small outbreaks and travel-related cases.

READ MORE: These tiny worms can survive forces 400,000 times stronger than Earth’s gravity

In 2023, Panama declared an outbreak. The outbreak continued moving northward as new cases emerged over the next two years in Central American countries. In 2024 cases were confirmed in Mexico, and in July a case was identified as close as 370 miles from the U.S. border.

As a result, sterile flies have been released in Mexico to curb the spread. In May, the USDA suspended imports of live cattle, horse and bison along the southern border. In June, the USDA announced an initiative to prevent a U.S. infestation including a $8.5 million sterile insect dispersal facility at an inactive air base in Texas.

“The state agencies and the federal agencies are preparing and have response plans ready to go, should something happen,” Kaufman said. “It is certainly a solvable problem. We are not without answers.”

Here’s What “Preaching to the Choir” Really Means

The meaning behind this common church-rooted idiom might surprise you

You’ve got something to say. No, it’s more than that—you’re fired up, ready to make your case about the brilliance of the show you just binge-watched or the ridiculousness of those 4 p.m. Friday Zoom calls. You gather your thoughts, find the perfect words and lay out your argument with conviction.

You hit your final point and look around, expecting to see at least a raised eyebrow. But instead? Total, enthusiastic, immediate agreement. Heads nod. Someone says, “Exactly.” Another adds, “I’ve been saying that for years.” And suddenly, you realize: You’re not changing minds. You’re preaching to the choir.

Which, let’s be honest, feels great­—but maybe a little pointless. But where does the expression preaching to the choir come from? And why has it stuck around so long? To find out, I turned to Grant Barrett, a linguist, lexicographer and co-host of A Way with Words, a national radio show about language.

Read on to unpack preaching to the choir’s meaning and to sing the praises of this spirited idiom.

Get Reader’s Digest’s Read Up newsletter for more humor, cleaning, travel, tech and fun facts all week long.

What does preaching to the choir mean?

Preaching to the choir is an idiom that means trying to convince someone of something they already agree with. It’s often used when someone is passionately making a case but to an audience that’s completely on their side. At the heart of preaching to the choir’s meaning is calling out the irony of convincing those who need no convincing. In other words, it’s a lot of wasted effort spent on people who don’t need persuading.

What is the origin of preaching to the choir?

Like many sayings, preaching to the choir has an interesting path from sacred spaces to everyday speech.

Religious roots

The phrase comes from Christian church services, where members of the clergy deliver sermons to the entire congregation. The choir is made up of regular, deeply involved churchgoers who sing at various points during the service. If you’re preaching to the choir, you’re speaking to those who are already on board with the message—perhaps more so than anyone else.

Secular spread

This idiom likely began circulating in American churches in the late 19th to early 20th century, but it didn’t become commonly used in secular conversation until the middle of the 20th century. “The earliest written record that I can find of it is the 1970s, but I bet it’s a lot older than that,” Barrett says. That’s when it began appearing in political and social commentary, often to point out when someone was passionately restating ideas to an already like-minded audience.

Today

Preaching to the choir has gone mainstream. You’ll hear it in politics, classrooms, newsrooms, boardrooms and even on reality TV to signal that an argument is falling on already-agreeable ears.

“It’s one of those idioms that I think passes unnoticed for a lot of people, certainly in politics,” says Barrett. “Politics is all about the art of persuasion. When you find yourself arguing with people who agree with you, and realize you’re preaching to the choir, the phrase kind of naturally falls out of your mouth because politics is about bringing people into the choir.”

Why is it a choir and not a congregation, pastor or priest?

The pastor or priest, typically, would be the one doing the preaching. But what about the congregation? The word choir is symbolically important, according to Barrett, because the group of singers is positioned behind the preacher; it’s both visually and practically ironic to direct a message at them. In addition, they are often the most dedicated or devout members, participating in services every Sunday and fully aligned with the church’s teachings. “Anybody who’s committed enough to the church to join the choir is probably not going to dispute the liturgy,” he says.

The phrase highlights the redundancy more strongly than preaching to the congregation would. The whole congregation may have varying beliefs, but the choir? They’re all in.

What’s the difference between preaching to the choir and preaching to the converted?

These two phrases are closely related and often used interchangeably. Preaching to the converted, says Barrett, is a much older form of the phrase (first recorded in 1857, per the Oxford English Dictionary) and comes from the United Kingdom. Preaching to the choir is more of a U.S. saying.

But there’s a difference in emphasis: The converted once needed persuading but no longer do. The choir never needed convincing to agree with you. “Preaching to the converted brings about the spirit of evangelism, which is the idea of really selling somebody on a religion or a religious point of view,” Barrett adds. “So I think preaching to the converted is even more striking in what it’s saying.”

Both phrases share a similar spirit, but preaching to the choir’s meaning leans more on irony than transformation—you’re addressing the already devoted, not the recently convinced.

How would you use the phrase preaching to the choir?

This phrase shows up in casual conversations, workplace discussions and social commentary to point out that someone’s argument is redundant or misdirected. Here are a few real-world examples:

• “Hey, I love the planet! You don’t need to convince me to recycle—you’re preaching to the choir.”

• “My manager keeps stressing how important deadlines are, but we’re the ones staying late every night. He’s definitely preaching to the choir.”

• “When I vent about online trolls to my friends in digital media, I know I’m preaching to the choir.”

• “The mayor gave an impassioned speech about climate change at an environmental conference. She was clearly preaching to the choir.”

• “Dude, you’re preaching to the choir. I’ve loved that band since middle school.”

What are some synonyms for preaching to the choir?

Looking for another way to say someone’s making a point to people who already agree? Try one of these alternatives to preaching to the choir:

• Stating the obvious.

• Singing from the same song sheet/song book. “It evokes the notion of singing together in church,” Barrett says. “You’re on the same page—literally. You’ve got the same lyrics, you’re reading the same thing, singing the same tune.”

• Beating a dead horse.

• Telling us what we already know.

• Carrying coals to Newcastle. This British idiom means doing something unnecessary, as Newcastle was historically a coal-rich city and didn’t need more coal.

So whether you’re rallying a team, debating an issue or just venting to friends, remember: The real challenge isn’t preaching to the choir—it’s finding ways to reach those outside it.

About the expertGrant Barrett is a lexicographer and dictionary editor who specializes in slang and new words. He is the co-host of A Way with Words, a national radio show about language, and has written several books, including Perfect English Grammar.

Why trust us

At Reader’s Digest, we’re committed to producing high-quality content by writers with expertise and experience in their field in consultation with relevant, qualified experts. We rely on reputable primary sources, including government and professional organizations and academic institutions as well as our writers’ personal experience where appropriate. We verify all facts and data, back them with credible sourcing and revisit them over time to ensure they remain accurate and up to date. For this piece on preaching to the choir’s meaning, Jo Ann Liguori tapped her decades of experience as a copy editor to ensure that all information is accurate and offers the best possible advice to readers. Read more about our team, our contributors and our editorial policies.