EL ROSARIO, Mexico
A tapestry of orange and black wings colors the white snow on a forest floor where thousands of monarch butterflies lie inert.
It's here in the mountain sanctuary of El Rosario , Mexico, where almost all of the North American monarch butterflies ( Danau plexippus) gather every year, seeking shelter from the winter cold in forests of pine and spruce trees.
Last week however, their seasonal refuge was interrupted by a rare snow and wind storm that toppled hundreds of trees in the area, surprising residents of El Rosario who not used to such weather at this time of year when the butterflies begin to head back to the United States.
The winds blew off several roofs of homes in El Rosario, located in the central state of Michoacán making access by car on icy roads impossible. Local officials closed the sanctuary until last Saturday, citing security concerns due to the ice and falling trees. However, a Univision team managed to climb to the heart of the reserve by foot, about 10,500 feet (3,200 meters) in elevation, on Thursday morning when the snow was at its deepest, and the situation of the butterflies at its most critical.
What they witnessed was a life and death scenario, recording rare footage of this small insect weighing only 0.01 ounces (0.5 grams) as they struggled for survival in the cold.
Climbing with the help of two local guards, over huge felled trees –some uprooted– the Univision team reached the colony of butterflies under a shroud of mist to discover the carpet of orange and black wings. Ressembling dead leaves, the butterflies continued to fall from the trees, making small circles in the air before dropping to the snow floor with a silent thud.
In the trees, some insects clung in bunches to tree trunks and branches covered in ice, as in a freezer.
"They are grouped, this way they are well protected from the cold and stay alive," explained Abel Cruz Resendiz, one of the local guides from El Rosario. "There is concern for those found on the ground, as they can freeze to death," he added.
Those responsible for the sanctuary say they have kept the mortality rate under 5% of the population, though in reality there has not been an accurate monitoring of the impact on the colonies, with no count of dead specimens. In fact, two days after the snowfall, butterflies continued to rain down from the trees.
Colonies of this lepidopteran species have resisted, but this unexpected blow is a new warning. "A storm like this is the worst situation for the species here," said Eduardo Rendón, coordinator of the Monarch Butterfly Program for the World Wildlife Fund (WWF) in Mexico , explaining that all the butterflies of the sanctuaries of Michoacán and the State of Mexico are concentrated in an area 9.9 acres (4.01 hectares), about four football fields. A snowstorm of longer duration could be lethal for the entire North American monarch.
Monarch butterflies: when snow threatens their survival
In this case, a species is not at stake, but rather only migration of its kind in nature. To get here, some of the butterflies colonies have traveled about 2,600 miles (4,200 kilometers) from Canada and the United States. "A person weighing 70 kilos would have to travel 14,000 times around the earth to match their trip," said Rendón.
As the sanctuaries begin to heat up again with March’s sun, it is expected that the clustered butterflies in the trees will come back to life. Two days after the storm some began to fly. In addition, others struggled to rise from the ground on wobbly legs.
This incredibly resilient species risks its life to migrate on orange wings; nature's parralel of the many thousands of immigrants from Mexico and Central America who risk all in search of a better life.
In a few days, those that survived will begin the journey back to the United States. That's when another amazing process occurs: the females who traveled to Mexico and spent the winter there will begin to lay eggs on milkweed plants in the southern U.S. - and then die. A new generation, which will live long enough to breed again on the journey, will continue to travel. In this way, generations multiply as they fly, scattering themselves north to recoup the species population. Each female can lay about 400 eggs and it will be the great grandchildren of those who leave the winter sanctuary who will make the trip back to Mexico next fall.
The most delicate situation for the species is when their numbers are down and they are concentrated in a few acres of their winter refuge. For Rendón, all that can be done to cushion the damage from the weather is to continue working on the conservation of Mexican forests and the prevention of illegal logging.
The reproduction phase in the United States is also key for the survival of the monarch's migration, said Rendón, a biologist who highlighted the use of pesticides that affect milkweed.
In the past, many more butterflies would come to winter in Mexico, he noted. The fewer there are, the harder it will be for this butterfly to survive another heavy snowfall.
Lea este artículo en español: Las mariposas monarca frente a la gran nevada de México