The inspiring journey of the Monarch butterflies is one that takes place every year, as hundreds of millions of butterflies travel thousands of miles from North America to their winter grounds in Mexico. Having puzzled scientists for decades, many had believed that the butterflies, each weighing less than a gram, used an in-built “map” to help them navigate the lengthy journey, but recent findings suggest they determine their location from the sun alone.
Following over five decades of research and gathering data from the Monarchs’ annual migration route, researchers tested out the common idea that the butterflies may have had a genetic, in-built map instructing them on the route to follow for their journey. But the results showed that the butterflies used a much simpler system, guided by the sun and magnetic fields acting as a natural compass to follow the route southwards.
Monarchs migrate each winter, with the journey usually commencing at the start of each October, or sooner if the seasons turn cold. Unable to withstand the freezing temperatures, winter hibernation is essential to their survival, and the return in spring is equally important, as larval food plants in the wintering grounds are insufficient to feed upon. Monarch butterflies hibernate in the central forests of Mexico, and are also known to use the same trees each year during the migration, despite the fact that each new arrival is a descendent many generations on from the previous year.
Monarch butterflies are a striking attraction during their hibernation period. Coloured in bright flame red wings with black veins and red spots, both male and female butterflies are large, with a wingspan of 4 inches. The larger males can be distinguished by black dots along their veins, while females are slightly smaller. While the story of the butterflies’ epic migratory path has captured the imagination of the public, they now face endangerment as extreme climate changes and destruction of the milkweed plant – an essential food for the butterflies, has increased due to herbicide use. Deforestation of the vital trees in which they hibernate has also heavily impacted their numbers, as shelter in the harsh winter months is destroyed due to extensive logging. Campaigners continue to call for conservation of essential areas for the breeding and hibernation of monarch butterflies, across the US, Canada and Mexico.
To catch a glimpse of these butterflies, visitors can often enjoy the sight of thousands of hibernating Monarchs at the Monarch Butterfly Biosphere Reserve, 100km north of Mexico City. As millions of butterflies fill the air each year, visitors to the site can discover a once in a lifetime experience, and take part in a unique natural phenomenon. The best time to visit the reserve is early February, when the butterflies are most active. From Mexico City, the reserve areas can be accessed by hiking or on horseback for the hour length journey, with the help of a local guide.