Hundreds of Monarch butterflies fly at the Pedro Herrada butterfly sanctuary, on a mountain in the Mexican state of Michoacan, February 1, 2011. The Monarchs are the only migratory insects in their species and travel 4000 kilometres (around 2500 miles) twice a year between their summer home in Canada and their winter home in Mexico. Picture taken February 1, 2011 REUTERS/Felipe Courzo (MEXICO – Tags: ENVIRONMENT ANIMALS) – RTXXEM2