Rabbles of Monarch butterflies cling to tree branches, in the Piedra Herrada sanctuary, near Valle de Bravo, Mexico on Jan 4, 2015. More butterflies appear to have made the long flight from the US and Canada to their winter nesting ground in western Mexico, raising hopes after their number dropped to a record low last year. But experts still fear that unusual cold temperatures will threaten the orange and black insects. [Photo/IC]