Crop circles — strange patterns that appear mysteriously overnight in farmers' fields—provoke puzzlement, delight and intrigue among the press and public alike. The circles are mostly found in the United Kingdom, but have spread to dozens of countries around the world in past decades. The mystery has inspired countless books, blogs, fan groups, researchers (dubbed "cereologists") and even Hollywood films.

Despite having been studied for decades, the question remains: Who — or what — is making them?