<P> Monarch butterfly migration is the phenomenon, mainly across North America, where the subspecies Danaus plexippus plexippus migrates each summer and autumn to and from overwintering sites on the West Coast of California or mountainous sites in Central Mexico . Other subspecies perform minor migrations or none at all . This massive movement of butterflies has been called "one of the most spectacular natural phenomena in the world". </P> <P> The monarchs begin their southern migration September to October . Eastern and northeastern populations, originating in southern Canada and the United States, travel to overwintering sites in central Mexico . They arrive at their roosting sites in November . They remain in their roosts during the winter months and then begin their northern migration in March . No individual butterfly completes the entire round trip . Female monarchs lay eggs for a subsequent generation during the northward migration . Four generations are involved in the annual cycle . </P> <P> Similarly, the western populations migrate annually from regions west of the Rocky Mountains to overwintering sites on the coast of California . </P>

Where do monarch butterflies go in the winter time