NEAR TLALPUJAHUA, MEXICO = We witnessed a remarkable phenomenon in the mountains above this lovely colonial town. There is huge annual migration of Monarch butterflies from Canada and the Northeastern United States to this mountainous region of Mexico, about a three hour drive from Mexico City. The Monarchs arrive in early November, which coincides with the Day of the Dead – the pre-Spanish people resident in the area believed that Monarchs were the souls of their ancestors. They cluster in very high density (estimated at about 20 million butterflies per hectare) at very high altitude. It’s possible to visit them by driving deeply into the the mountains and riding a horse for about a half hour from a nomadic base camp. It’s possible to walk, but not advised because the elevation is very high, 11,200 feet (3,400 meters) and the half day one is there is too short a time to become acclimatized to the altitude. The Monarchs cluster quietly on every surface until the temperature goes above 50 degrees F at which point they take to the air in breathtaking density, The Monarchs we see in Connecticut take part in this migration.