Monarch butterflies cannot survive the cold winter weather in the United States so they migrate south and west each fall. This migration usually starts in October.
The monarch butterflies spend their winter hibernation in oyamel fir trees in Mexico and eucalyptus trees in California. They use the very same trees each year when they migrate which seems odd because they are not the same butterflies from the previous year.
These butterflies are the only insect that migrates to a warmer climate that is 2,500 miles away. Visit here for more interesting facts.