Monarch butterflies wintering in Michoacán, Mexico

The migrating monarchs of Michoacán

Every autumn, millions of these striking monarch butterflies embark on one of the world’s most amazing migrations from North America to the mountains of western Mexico. They travel up to 3,000 miles south on air currents - a huge distance for these delicate insects, to a place none of them has been to before. And unlike migratory birds, these particular butterflies will never return to the north – they simply won’t live long enough.

The monarchs travel here to the mountains of Michoacán, Mexico, in search of a safe, warm place to spend the winter. They huddle together on trees known as sacred firs, which create the ideal microclimate for them and they stay here through the winter until March, when they begin to fly back north. After a relatively short distance, these monarchs will stop to mate and lay eggs on milkweed plants. The eggs will hatch after just a few days, creating the next generation of butterflies to continue the trek back north. The whole cycle takes several generations to complete. So how do they know where to go? Scientists aren't exactly sure, but they think monarchs use the sun as a compass and are compelled to migrate to follow the flowering path of their food source, milkweed.