Monarch butterflies take flight in a fir forest in central Mexico, where more than one billion of the insects migrate annually to a small mountainous region in Michoacan State and Mexico State. (+NatureStock)
Overnight temperatures in the fir forests of central Mexico hover just above freezing in January. It’s the ideal temperature for the enormous colonies of monarch butterflies that, in late August, begin their 3,000-mile migration south to this small mountainous region. They overwinter u