<P> Monarch butterflies (Danaus plexippus) perform annual migrations across North America which have been called "one of the most spectacular natural phenomena in the world". </P> <P> Starting in September and October, eastern and northeastern populations migrate from southern Canada and the United States to overwintering sites in central Mexico where they arrive around November . They start the return trip in March, arriving around July . No individual butterfly completes the entire round trip; female monarchs lay eggs for the next generation during the northward migration and at least four generations are involved in the annual cycle . </P> <P> Similarly, the western populations migrate annually between regions west of the Rocky Mountains including northern Canada and overwintering sites on the coast of California . </P>

Where does the monarch butterfly go in the winter