Right about now, thousands of Monarch butterflies are beginning to make their way from North America's colder regions to their winter homes in California and Mexico, where they will spend the season hibernating, before heading back in early spring next year. 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 who live between 6-8 weeks, it is only the ones that are born around September and October that make that trek.
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 grandkids! Yet, they all make the same round-trip each year. The ones from North America's East Coast head to Mexico, while those living west of the Rocky Mountains fly down to California. So how do they know exactly where to go and more importantly, where to return?
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, because 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 grandkids, depending on how long the return journey takes, that find their way back to their summer homes with the help of their in-built GPS devices. Simply fascinating isn't it?