Going up into the Monarch Butterfly Biosphere Reserve, between the Mexican states of Michoacán and Estado de México at an altitude of almost 10,000 feet, can be dizzying. The flashes of orange catch the corner of your eye, dart around your shoulders and streak above in the sky. Neon in your face, rustling your hair and eyelashes, as you realize you are surrounded.
Butterflies crowd the horizon, litter the walking path and tremble on the green leaves of the trees in which they nest. They circle and smash into visitors, who are encouraged to stay as quiet as possible so as not to disturb the fragile insects.