This is the season for crop circles, and each year their designs seem to grow more elaborate. One recent circle in Wiltshire is so sophisticated it depicts the mathematical formula pi (News, June 17). The circles first hit the headlines in 1980, but eventually they were revealed as hoaxes.

However, crop circles have been around for centuries. One was clearly illustrated in a woodcut from 1678 inscribed: “The Mowing-Devil: Or, Strange News Out Of Hartford-Shire,” in which a field of oats was reportedly scythed down by the Devil during the night. “The Crop of Oats hew’d as if it had been all of a flame: but next Morning appear’d so neatly mow’d by the Devil or some Infernal Spirit, that no Mortal Man was able to do the like.”

In 1880 the science journal Nature carried a report of crop circles in Guildford, Surrey, after a thunderstorm. “We found a field of standing wheat considerably knocked about, not as an entirety, but in patches forming, as viewed from a distance, circular spots,” the correspondent wrote.

One clue to how crop circles might be made by natural forces was seen in July 2002 in Canada. During a thunderstorm, several small vortices were seen landing in a wheat field and leaving circular patterns behind.