It was a blood-boiler of a story, a menacing tale of government gone too far: The Environmental Protection Agency was spying on Midwestern farmers with the same aerial “drones” used to kill terrorists overseas.

This month, the idea has been repeated in TV segments, on multiple blogs and by at least four congressmen. The only trouble is, it isn’t true.

It was never true. The EPA isn’t using drone aircraft — in the Midwest or anywhere else.

The hubbub over nonexistent drones provides a look at something hard to capture in American politics: the vibrant, almost viral, life cycle of a falsehood. This one seems to have been born less than three weeks ago, in tweets and blog posts that twisted the details of a real news story about EPA inspectors flying in small planes.

Then the falsehood spread, via conservative Web sites, mentions on Fox News Channel and Comedy Central’s “The Daily Show,” and the endless replication of Twitter. In its mature stage, the idea was sustained by a digital echo chamber. Congressmen repeated false reports — and then new reports appeared, based on the congressmen.

“We’ve never thought that. We’ve never said that. I don’t know where it came from,” said Kristen Hassebrook, at the association of Nebraska Cattlemen, when asked about drones buzzing cattle farms. Her group seems to have started this hubbub, then watched as its actual complaint against the EPA was turned into something it wasn’t. “But obviously the word ‘drone’ is a very sexy word.”

This is the part that’s true: For more than a decade, EPA inspectors have flown over farmland in small private planes — the traditional kind of aircraft, with people inside them. The inspectors are looking for clean-water violations, such as dirty runoff or manure dumped into a stream.

The EPA says the flights are legal, under a 1986 Supreme Court decision. And they’re cheap: An on-the-ground inspection might cost $10,000, but it costs just $1,000 to $2,500 to survey the same farm by air. An agency spokesman said these flights are not happening more frequently now than in the past.

But in Nebraska, the cattlemen have raised new concerns about the effect of the flights.

“It is truly an invasion of privacy,” said Chuck Folken, who runs a farm and cattle feedlot in Leigh, Neb. Farmers worry about photos of private homes and back yards winding up in government files. “We don’t need our own government . . . flying over us, taking pictures of us, telling us what we’re doing wrong.”

On May 29, Nebraska’s congressional delegation — four Republicans and a Democrat — wrote a letter to the EPA, asking questions about the aerial surveillance. Because the concern was about airplanes, their letter didn’t say a word about drones.

But soon enough, somebody did.

First a couple of Twitter users got it wrong. Then, at 2:51 p.m. June 1, the Web site pjmedia.com posted a blog item with the title, “EPA Using Spy Drones to Fly Over Midwestern Farms.” It provided a link to a report on the Fox News Web site — which discussed the lawmakers’ letter but didn’t actually mention drones.

That same afternoon, the falsehood spread to television. On a Fox News Channel “ensemble opinion show” called “The Five,” Fox contributor Bob Beckel said,“They are drones, they are flying overhead.”

“No, they’re not,” said fellow panelist Dana Perino, who served as White House press secretary under President George W. Bush. “They’re taking pictures.”

“No, no, no. They’re drones,” Beckel said.

Over the next three days, the story appeared on blogs, was tweeted and re-tweeted. It had all the makings of a great rumor. It combined two ideas that many people already believed to be true: that domestic use of drone aircraft was soon to increase, and that President Obama has used environmentalism as a cover for government overreach.

On June 5, the falsehood hit a growth spurt.

“Republican lawmakers are demanding answers today after learning the Environmental Protection Agency has been using aerial spy drones for years to spy on cattle ranchers,” Fox News Channel’s Megyn Kelly told viewers. “These are the same drones we use to track down al-Qaeda terrorists, flying over Nebraska and Iowa.” Asked about the source of Kelly’s report, a Fox News Channel spokeswoman declined to comment for the record.

Two days later, “The Daily Show” made fun of Kelly but repeated the falsehood: “Those aren’t the same drones!” Comedy Central’s host Jon Stewart said.

On June 6, the fast-moving rumor made it to Capitol Hill.

“The Obama Administration has, once again, stepped way over the line,” Rep. Denny Rehberg (R-Mont.) said in a news release. He was sending a letter to the EPA, responding to “reports” about drone use. “First they wanted to expand their authority to regulate water, and now they want to use air drones to spy on American citizens.”

On the same day, an editorial in Investors Business Daily described “drone” flights. At EPA headquarters, a spokesman said, the first inquiries about EPA drones began coming in. Representatives said they weren’t true.

Too late. The day after that, three more congressmen complained. Reps. Todd Akin (R-Mo.) and Tom Latham (R-Iowa) wrote their own letters about the reports of drones. And Rep. Jeff Fortenberry (R-Neb.) described his worries about drones in the “AgMinute” radio address released weekly by the House Agriculture Committee. Fortenberry cited “press reports” that the EPA “has been using military-style drone planes to secretly observe livestock operations.”

Here was the echo chamber at its peak. Fortenberry himself had signed the original, drone-free letter from the Nebraska delegation, whose misinterpretation had begun the drone rumors in the first place.

At this point, nine days later, the false reports about his own statement had reverberated around the country, and found their way back to Fortenberry. And the lawmaker appeared to treat them as something new — and alarming.

Fortenberry’s radio address set off a new round of echoes, with online outlets repeating his worries about the drones.

In the days since, the truth has begun, slowly, to rouse itself and stagger after the lie.

A spokeswoman for Fortenberry said he now accepts the EPA’s account that no drones exist. Fox News said on June 10 and 14 that the flights were done by planes, not drones. On Monday, a day after this story appeared in The Washington Post, Fox’s Megyn Kelly read a “clarification” on air:

“We identified and discussed the aircraft as being unmanned drones,” Kelly said. “In fact, the EPA is flying these missions and taking pictures from manned aircraft. We apologize for the confusion.”

On Friday, after a Post inquiry, PJ­Media told its readers the same thing: “We’re happy to report that the EPA denies this.”

Other conservative media outlets such as the Daily Caller and the New American, which had reported on the EPA drones, also told readers that the agency denied their existence.

But the falsehood was far ahead, still replicating itself. By week’s end, the second Daily Caller report — which said the drones did not exist — had been posted just 14 times on Twitter, and recommended by 30 people on Facebook.

The first article, which said the drones were real, was still going: It had 233 Twitter mentions, and 661 recommendations on Facebook. No, wait, 662.

Staff writer Rosalind S. Helderman and staff researcher Alice Crites contributed to this report.