They grow to just 10cm (4"). Their distinctive orange and black wings are like starched tissue paper. Their life-span is a mere two to eight weeks, yet they will fly through storms and natural predators to complete their journey. They fly up to 161km (100 miles) a day, at altitudes of sometimes 3km (10,000ft); crossing in all terrains, from mountain to jungle, to city, to wetlands, to the Arizona desert, to the coast, to the Georgia woodlands and beyond. They are the only butterfly to migrate, like birds, rather than hibernate over winter.
Monarchs are the stars of a Mexican government tourist compaign; and the mascot insect/butterfly of no less than six American states. The Aztecs believed them to be the airborn souls of their departed warriors. Even today, some of the older Mexicans will step aside for the passage of the monarch butterfly, viewing them as carrying away the spirits of their dead. (It is a story that resonates across the world in Ireland, where white butterflies or moths perform the same service.)
To the Tohono O'odham tribe, of Northern Mexico and Arizona, the monarch butterflies caused wishes to be conveyed to the gods. Catch one and whisper your secret need, then let it go. The gods will hear. It is this that has fuelled a growing industry in monarch butterly releases, at weddings and funerals, all over the USA. That and, of course, the vision of hundreds of pretty butterfly wings, soaring like petals in the air, as something beautifully special to mark the momentous occasion.
For the Guatemalan Maya, the significance of the monarch butterfly was more philosophical. The butterfly's twin wings represented the dream world and the waking world. It could only survive if the two touched constantly, and met in the heart. It was a message to us all, that dreams and reality were equally important; and one should be dismissed as fancy only at our peril.
The monarch butterflies are on their way back. They left the central Mexican highlands in February to fly northwards, passing the border into America. They summered, supping on the nectar of those countries' flora, but as August turns, the monarchs start to head back down, ahead of the northern frosts.
En route there, the females would have deposited eggs, on the first milkweed growth that she found. These have now hatched into caterpillars. Three weeks later, the caterpillar is a monarch butterfly too, living out its eight weeks in an American garden, or flying northwards too. Its children, or grandchildren, might make it into Canada.
But then they turn, this descendent monarch, hearing the impulse of its ancestor to head to the warmth of the Sierra Madre. It will die before it makes it to the Mexican border. But its child or grandchild will cross and eventually settle, swarming the oyamel trees, until not a leaf nor inch of bark can be seen. It's like a gigantic relay race of the generations, ensuring their species' survival.
Monarch butterflies covering a Mexican tree.
Yet human beings haven't helped in that task. Monarch butterflies are not endangered, but there was a real fear that they could rapidly become so. For many years, the major problem was illegal logging in Mexico itself. However, that has dramatically decreased, since the loggers realised that there was more money to be had in butterfly tourism, than in selling the timber.
They have also been assisted by the establishment of state-funded butterfly sanctuaries, throughout the migration route. These vast areas span more than 790,000 h (1,951,300 ac) under the jurisdiction of 22 different municipalities; 12 in the State of Michoacan, and 10 in the State of Mexico. In Michoacan alone, over 500,000 oyamel trees have been planted to combat the logging losses of the past.
A handful of these sanctuaries are open to the general public. El Rosario and Chincua are in Michoacan; while Cerro Pelon, Herradura and La Mesa are in the state of Mexico. The revenue from their guided tours and amenities help to secure the protection of the legendary monarch butterflies. El Rosario has been declared an UNESCO World Heritage site.
But despite all of this, the numbers of monarchs fell sharply this year. A study from the World Wildlife Fund showed that only one-fourth of the amount of monarchs leaving Mexico, returned last year. There are several theories as to why. February is usually one of the driest months in Mexico, but last year, the oyamel trees, with their cargo of monarchs, was lashed by sleet and rain in a freak storm. As a result, fewer survived to even set off north.
This has worried Juan Bezaury, Mexico's representative for The Nature Conservancy, who told reporters, "We can say that extreme climate events will be more frequent and more intense." It is a concern that is likely to be included in the UN Climate Change Conference, being held in Cancún, in December 2010. Mexico has already promised to reduce carbon emissions, by 50 million tonnes, in 2012.
Then there are the dangers north of the border. Pollen from genetically modified corn, in the United States, has been blowing onto the milkweed - the favoured food of the monarch butterflies. This pollen is toxic to them and has been killing them in their thousands. Also herbicides sprayed onto roadsides, coupled with rigorous mowing to keep them neat, have been destroying the same milkweed. Meanwhile, blackwort has been able to thrive. This plant looks very like milkweed, but is poisonous to the monarch caterpillars. Mexican, American and Canadian officials are working together to see how these issues might be resolved.
For now, everyone is waiting, in wondrous anticipation, to witness November's grand return. They will be here until February, wintering amongst the oyamel trees. It is one of nature's most sublimely magical spectacles; and one which will see the crowds flocking into the sanctuaries to dream and watch and simply be a part of it.