Monarch butterflies (Danaus Plexippus) perform annual migrations across North America which have been called “one of the most spectacular natural phenomena in the world”.
Starting in August, northern monarch populations begin migrating from southern Canada, through USA, to overwintering sites in central Mexico. They arrive in November, where they hibernate through the winter. 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 four to six generations are involved in the annual cycle.
Monarchs also perform small distance migrations in Australia and New Zealand. There are also some populations in south America and certain southern states that do not migrate.