Around this time each year, thousands of Monarch butterflies will make their way from North America's colder regions to their winter home in California and Mexico, where they will hibernate before heading back in early spring. This round-trip, which in some cases spans about 2,000 miles each way and can take as long as two months, is unique and fascinating for a number of reasons.

First and foremost, it is very unusual for insects to migrate - That's because most of them do not have a lifespan long enough to extend from one season to the next.

In fact, even amongst the Monarch butterflies, it is only the ones that are born around that September and October - The ones that migrate - that survive long enough to trek between seasons. The life span of Monarch butterflies born any other time of the year is between 6-8 weeks.

What's even more amazing is that they travel to the same destination each year. The ones from North America's East Coast head to Mexico, while those from living west of the Rocky Mountains fly down to California.

Not impressed? You will be, when you find out that the Monarchs that fly in are not the same ones that fly back - They are the kids or in some cases grand kids! So how do they know exactly where to go? That, is the most fascinating part of the migration.

To get to their destination, the butterflies follow the direction of the sun. However that is not easy as it sounds, since the thanks to the Earth's rotation, the sun is constantly moving. So, this is how they do it.

First with the help of a 24-hour body clock, known as circadian clock that lies in their antenna, the butterflies deduce whether it's 8 in the morning or 4 in the afternoon, This helps them figure out whether the sun should be on the right or left. Once they know that, they follow the angle of the sun, which is captured by special cells called photoreceptors that sit inside their eyes to get to their destination. Scientists have dubbed this surprisingly sophisticated system - time adjusted sun compass.

Once they get to their destination in California or Mexico, they spend the winter living off fat reserves. Around February and March, they reawaken, and start their trek back - Along the way they lay eggs and die. It's therefore the kids or even grand kids, depending on how long the return journey takes, that find their way back to their summer homes thanks to their in-built GPS devices. Simply fascinating isn't it?