Each fall the 5th generation of Monarchs from the eastern United States and Canada migrate up to 3500 miles to an area near Mexico City in the mountains at about 10,000 feet and settle down for the winter months. Their congregation amounts to about 300 million butterflies. These Monarchs settle in the same trees as their great, great grandparents did the year before. They do not feed and live off the fat they collected on the trip from flowers. In the spring they begin to mate, produce eggs, and they leave the site for the north. They lay their eggs on the way to produce progeny and die before reaching their original home. How they make this trip to the same site each year is one of the world's great mysteries.