A mysterious force haunting the British countryside is enthralling observers, baffling scientists and infuriating farmers.
The season of crop circles is here again, with more than 50 sightings already reported of strange formations appearing in fields across southern England.
Some experts believe the formations, ranging from simple circles to huge intricate designs, could be traces left by UFOs (unidentified flying objects) or signs from spirits trying to communicate with man. Others blame pranksters or the weather.
"This is an extraordinary phenomenon; there's been nothing like it in recorded history," said Michael Green, chairman of the Center for Crop Circle Studies (CCCS), a body of scientists and mystics set up two years ago to study the enigma.
Green said the phenomenon started in Britain 12 years ago, when three round areas of flattened crops, each about 60 feet across, appeared in oat fields near the southern town of Westbury.
Sightings in the early years amounted to a few simple circles. But then the number, size and complexity of shapes increased dramatically.
The CCCS has organized an international conference on crop circles. It has so far recorded more than 2,000 sightings, mainly in southern Britain but also across Europe, the United States, Canada and Japan.
But an army of skeptics argue that they are merely the work of hoaxers.
One landowner even organized his own competition in this month among the cream of Britain's crop circle hoaxers and offered a $5,700 prize for the best fake.
A dozen teams gathered in fields in Buckinghamshire, southern England, to flatten the corn using baseball bats, pipes, ladders and planks.
They were helped by a Pyrenean mountain dog called Yeti, trained by his owners to pull a plank to flatten the crops.
Such antics do not amuse the likes of photographer Peter Glastonbury, one of many amateur enthusiasts who will spend the summer months scouring their local countryside for crop circles.
Glastonbury has spotted two formations so far this season, including a dumb-bell shape near the southwest port of Brixham.
After examining the formation--a 50-foot circle and a 26-foot circle joined by a 6-foot channel--he is convinced that it is not man-made.
"There are usually telltale signs when people have faked it, such as tracks across the field," explained Glastonbury, who saw a similar pair of circles in the same field last year.
Until 1989 circles were found in simple groups or surrounded by rings or satellites.
But the last two seasons have produced startling new patterns, with triangles, boxes and key shapes joined by channels into elaborate designs or pictograms, often hundreds of feet long.
"There is clearly an intelligence of some sort behind this phenomenon," said Green, a retired archeologist who has recognized symbols from ancient religions and modern science in many of the formations.
Green suggests that the circle makers may be ancient spirits trying to warn humanity about the deteriorating state of the planet.
But for some scientists the answer lies in natural forces.
Physicist Terence Meaden, who has devoted the last decade to unraveling the circles mystery, believes a type of whirlwind, known as a plasma vortex, can produce round traces in standing crops.
"There is no question at all that a few, rather plain round circles are genuine. All the rest are fakes," said Meaden, who heads an international research group CERES, named after the Roman corn goddess.
Glastonbury is in no hurry to solve the enigma. "Maybe they are giving us a set of symbols and at the end we have an alphabet to work with," he said.
Physicist Robin Allan, who fooled experts last year by creating a crop circle, continues to attack the theorists.
"If little green men really did want to come down to Earth and make fools of us, they'd run for government, not do this," he said.