Saturday, December 03, 2011

A buttferfly's 2000 mile journey

Every summer, the North American Monarch butterfly embarks on a remarkable journey that begins in Canada or the northeastern United States. In two months, millions of these butterflies congregate in a high forest in Mexico. Each day, the butterfly travels fifty miles and the total journey is around two thousand miles.

Birds of course can fly even longer distances. But then birds also travel in groups: there are older members in the group who have covered these distances before and are therefore in a position to guide others. The Monarch butterfly makes the journey alone and it does so only once. When a Monarch butterfly starts from Canada, it has never flown before. No one is there to guide it to Mexico.

And yet, this delicate creature, with wings less than four inches wide, crosses the Great Lakes – imagine crossing these massive bodies of water, where there are few opportunities for nectar and rest – then Midwestern towns, the Great Plains, the deserts of Texas, the Sierra Madre range in Mexico, and makes its final approach to forests in Michoacan, 100 km northwest of Mexico City.

Some unknown compass – either the earth’s magnetic field or the sun – seems to tell it exactly where to go. Even when these butterflies are tagged for study are taken off course by scientists (say far to the east or west), they still recover and know exactly how to adjust their path.

Nature always throws up these inexplicable and mysterious examples. Why should we believe in the unverifiable miracles advertised by organized religion – that the Buddha was enlightened, that Krishna lifted a mountain, or that Jesus walked on water – why even think of them when the miracles of nature are much more tangible, more varied and can be observed every day?

The butterflies start from very different regions in the northern US and Canada, thousands of miles apart, but as they approach Mexico, they start to cluster together and can be seen in their hundreds of thousands in Texas as they narrow in on their destination. In the forests of Michoacan, they congregate in the millions, covering the skies, the forest floor, the trees, the twigs – just about everything. What started as a lone journey now culminates in the collective blanketing of a destination they were drawn to.

As they hang from the branches of trees, they look like leaves themselves -- see picture to the left.

The Monarchs rest in Michoacan until spring, and then begin the journey back. But no butterfly ever makes it back to Canada. About a third of their way back – around Texas – they mate and die. The few hundred eggs that each female lays then transform into butterflies and continue the journey. But this generation too does not make it all the way back. About halfway or three quarters of the way back is another mating cycle and the third generation continues the reverse migration. In the end, what we have is an incredible intergenerational relay spanning four generations. As they move northward, the butterflies begin to disperse geographically, eventually reaching original regions where the epic southward migration began.

For some reason, no single butterfly ever completes the cycle, but the generation that is born in Canada and reaches Mexico is the one that lives the longest.


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reNUka said...

Very interesting! Keep writing.