A crop circle in a field of oilseed rape at Roundway, Wiltshire, created on 29 April. The 2009 season began with an unprecedented six formations in April. Michael Glickman, an expert on the phenomena, said: "I've seen the odd [crop circle] in rape fields previously but this year I know of 11 giant yellow circles that have appeared this month alone. The crop is tougher and more brittle than corn or barley so it's mind-boggling to think how the intricate designs have been made"

A crop circle in a barley field near Devizes, Wiltshire, created 24 May. Each summer, the Wiltshire countryside is host to the crop circle phenomenon. The county, with its fields of rape, barley and wheat, is one of the most active areas for crop circles in the world, particularly around the historical stones of Avebury and Silbury Hill

A crop circle in a field of oilseed rape at Roundway Hill, Wiltshire, created on 10 May

A crop circle in a field of oilseed rape at Peaks Down, Swindon, Wiltshire created on 9 May. There have been more than 20 major crop circle formations spotted so far this year

A crop circle in a field of oilseed rape at All Cannings, Wiltshire created 6 May. The circles can take the shape of DNA structures, scorpions, snowflakes, helices, webs, knots and complex geometric patterns

A crop circle in a field of oilseed rape at Clatford, Wiltshire created on 4 May. Most crop circles are made by humans, primarily as hoaxes, but some believe that unexplained circles are the product of alien spacecraft or supernatural processes

A crop circle in a field of barley at Wroughton, Wiltshire created 24 May. The crop circle season in Wiltshire extends from April to harvesting in September, and is believed to be worth millions of pounds to the local economy