Crop Circles

This 1678 pamphlet (relating a farmer's Deal with the Devil gone bad) may be the first recorded claim of paranormal crop circle activity.

Crop circles are large geometric patterns that appear in fields of crops, usually corn (because cornfields are creepy), and are created by flattening the stalks in such a way that each individual one remains undamaged. They are usually presented as being supernatural in origin, with the most common explanation being that they were created by extraterrestrials, although the reasons behind why aliens visiting Earth would want to do such a thing varies.

In fiction, the question of who's going to pay for the vandalized crops never seems to arise.

Examples of Crop Circles include:

Comic Books

In a Duck comic, Donald Duck and Daisy visit Ireland and discover Crop Circles are created by dancing fairies.
One X-Files comic has Mulder go to a Crop Circle in progress and discovers a kid with a board and a flashlight flattening the stalks. The kid gets away, and may not have actually existed.

Film

The movie Signs features a few of these, as it's a movie about aliens.
- Parodied in Scary Movie 3. The aliens forgo tracing intricate symbols and simply draw a huge arrow with the words "ATTACK HERE".

Literature

In Lords and Ladies, the impending visitation of the elves causes crop circles to spontaneously generate in everything from an herb garden to a handful of seeds sprouting in a damp cloth.
- And lets not forget the Dean's scalp.
In Martians in Maggody, the appearance of crop circles in moonshiner Raz Buchanon's field draws a horde of UFO fanatics to the little Arkansas town, eager to photograph (for $10 a head, payable to a grinning Raz) this "inexplicable" phenomenon.

Live-Action TV

Dark Skies: they build a crop circle to try to lure the aliens into landing, so they could capture them. (Trivia: this episode came out very shortly after the guys who claimed to have started the crop circle phenomenon revealed themselves as hoaxers.)
In the episode "Vanished" of NCIS the team investigates crop circles and discovers one was caused by a helicopter and the others by the murderers attempting to cover up their crime.
In an episode of Drop the Dead Donkey Damien is in the newsroom when Dave takes a phone call, covers the mouthpiece with his hand and shouts across to him, "It's the farmer on the phone, wants to know how big you want him to make the crop circles."
In the Doctor Who episode "Let's Kill Hitler", Amy and Rory contact the Doctor by making a crop circle of his name when he wasn't answering his phone.

Music

The outer cover of Led Zeppelin's Box Set shows the shadow of a zeppelin passing over an elaborate set of crop circles, although on closer inspection the "cornfield" in which the circles have been cut looks suspiciously like a carpet.

Newspaper Comics

In a Zits strip, Pierce thinks aliens are leaving crop circles in his hair in an attempt to communicate with him. It turns out just to be bed head.

Video Games

In Spore, during the Space Stage, you can use Crop Circles to "communicate" with more primitive (meaning "not in space yet") species. There doesn't seem to be any real game effect, but they look cool.
Crop circles can appear in farm fields in SimCity 3000 when UFO attacks occur.

Western Animation

One episode of Invader Zim has Dib job-shadowing a paranormal investigator who takes him out to investigate some crop circles. Dib quickly points out that they're caused by a cow which is rolling back and forth across the field.
In Rocko's Modern Life, Heffer is working as a groundskeeper in a golf course and he keeps making crop circles with his lawn mower. At the end of the episode, aliens look at the circles and ask "Who keeps writing this stuff?"
On the first episode of South Park, a report on alien sightings features a crop circle formation in the exact likeness of Cartman, who has been implanted with an alien probe.

Cartman: Hey! That looks just like... Tom Selleck.

The Pixar Short "Unidentified Flying Mater" had Mator create crop circles shaped like tires.

Web Original

Barking Crayon reveals: it was Bigfoot. And he's annoyed that aliens and hoaxters took the credit.

Real Life

Crop Circles are usually made by farmers or others out to prank people. They take a board with a string, and stand on the board, moving it by the string, so that it flattens the cornstalks without breaking them. Or something like that. They also lead to millions of conspiracy nuts.
- Crop circles' frequency of appearance closely follows the change in value of the crops.