February 28, 2020 4:19:10 pm
Imagine this: You weigh less than one gram. You have tissue-thin wings, powdery to the touch — fiery orange and striped with black. Your filament-thin antennae and eyes are equipped with navigation and visual hardware that any GPS supercomputer would be proud to possess. If you break out of your chrysalis in around August or September — you are not interested in the opposite sex. Yet. But you do begin to hanker for mass company. You may be born in Canada or the Northeastern United States. Even if those countries have no time for kings and queens, you are called the Monarch. You don’t exactly have the aerodynamic shape of a bird. You fatten up on nectar, and wait until that day when an alarm clock goes off inside you.
Along with millions of your compatriots you take to the skies. Ahead stretches a 3,000-5,000-mile journey, southwards or south-westwards depending on your home base. Your final destination may be eucalyptus groves in southern California or the famous oyamel fir trees in the mountains of central Mexico. Here, with millions of compatriots you will cluster on the trees, your wings sounding like the soft rustling of a breeze, happy with the comfortable constant temperatures and still air. Here, you will rest until the increasing length of day will trigger yet another alarm. It is time to return. But you will never make it home again.
You are, of course, the fabled Monarch butterfly, native to North America and a poke in the eye for those opposing migration. In India and Africa, you have cousins — such as the Striped Tiger and Plain Tiger, who do not embark on such perilous journeys, apparently because they don’t have the specific travellers’ genetic component.
The annual migration of the Monarch butterfly in the US is surely one of Mother Nature’s technological triumphs. Two separate populations are found — one in Canada, the other in the Northeastern US. The butterflies that hatch towards the end of summer are just not interested in the opposite sex or for that matter, establishing territories. Instead, they are built for “endurance flying”. As the autumn chill begins and the days shorten and food supply diminishes, the butterflies know it is time to leave. Those setting off from Canada will fly along the coast, west of the Rockies down to southern California. Those setting off from the Northeastern US will fly down to the mountains of Mexico. Sometimes, these two groups mix and match. In their wintering grounds, they will cluster thickly together, conserving energy. By around the following March, they wake up and set off: some heading north to Canada, others north-east. They will fly relatively short distances, say, a few hundred miles, seeking out the food plant of their babies: the milkweed. They will mate, lay eggs and die. Their eggs will hatch, develop into caterpillars which will gorge on the milkweed before becoming chrysalides, out of which the newly-minted generation will emerge.
These will, so to speak, pick up the baton dropped by their parents, and continue the journey northwards. One suggestion was that they simply follow the progressive blooming of the milkweed. But how do they know that milkweed will be blooming further north rather than in any other direction? The only answer seems to be instinct. By the time they reach their “home,” which they have never seen before, they’ll be the fourth or fifth generation. Their ancestors, who embarked on marathon south-bound odysseys, lived for up to nine months. They will live perhaps for just five-seven weeks. Their ancestors were built for endurance flying, they are not.
Watching any butterfly fly in its typical drunken, tipsy way, I always wonder how they manage to land on a chosen bloom. The gentlest breeze can blow them off course. And here, there are these guys embarking on journeys spanning a vast continent, and arriving at their destination safely time and again. Apart from battling winds, they have to orient themselves correctly. Scientists seem to agree that they use the position of the sun to set their direction, as well as the earth’s magnetic field, for which sensors are located in their antennae. In addition, they may use physical features of the landscape — coastlines, rivers, lakes.
Apart from the weather, they have to survive attacks from predators. Birds do get after them — but as they’ve imbibed toxins from the milkweed (when they were caterpillars), they are largely unpalatable. They are subject to attacks by parasites too: it’s thought that the butterflies setting off relatively early in autumn are stronger than those setting off later, because parasite infestation increases as time passes and weakens them.
More than that, perhaps, is the threat they face from climate change and habitat degradation. While the areas around the oyemal pine groves in Mexico are protected, avocado plantations are eating into these, reducing the area available for the butterflies. The annual spectacle has also become a tourist attraction: imagine millions of bright orange butterflies festooning every tree around you, and, finally, one day, taking to the skies. At the moment, they are not endangered, though numbers fluctuate wildly from year to year and do seem to be heading downwards.
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