Every spring, shades of purple and blue glitter above the freeways, as tens and thousands of purple crow butterflies migrate from southern to northern Taiwan for the breeding season. In the fall, they reverse course and fly back south to hibernate.
“The migration is an extravaganza,” said Chan Chia-lung, a longtime butterfly researcher and doctoral candidate at National Taiwan University’s Institute of Ecology and Evolutionary Biology.
It is a spectacular sight indeed, but the delicate butterflies are also vulnerable to traffic. To prevent them from being hit by cars, in 2007 Taiwan’s National Freeway Bureau set up nets at critical points along the freeway. The four-meter high nets force the butterflies to fly higher, well above the passing vehicles, Chan said.
Once the number of butterflies reaches more than 500 per minute, lanes on the freeways have to be closed, he added. Taiwan is the first nation in the world to have instituted freeway closures for butterflies, Chan said, adding that the BBC and the National Geographic Channel have reported on the policy.
Taiwan is home to four subspecies of the purple butterfly—the Euploea mulciber, Euploea eunice hobsoni, Euploea sylvester swinhoei and Euploea tulliolus koxinga Fruhstorfer. A common feature they share is that the purple scales on their wings can change into violet or blue depending on wing movements and the observation angle, Chan explained.
Another unusual trait shared by the subspecies is that they are able to live as adults through winter, something rarely found among butterflies, according to Chan.
In fact, he added, Taiwan and Mexico are the only two places in the world where the impressive sight of butterflies migrating in winter can be seen. In other countries, such as Japan and nations in Europe, the winter months are simply too cold for the insect to live.
“Taiwan actually has more butterflies in winter than in all other seasons,” Chan said. “This is because the country straddles subtropical and tropical regions where purple butterflies are distributed.
“So in winter, the butterflies follow their instincts and journey south, where it is warmer.”
The winter habitats of purple butterflies are found in the mountainous areas of Pingtung County and Kaohsiung City, both in southern Taiwan. “The valleys they live in must face south and be surrounded by forest, and their habitat must be situated on the leeward side of the valleys—if not, they would die whenever the northeasterly monsoon rains sweep in,” he explained.
According to Chan, purple butterflies were first discovered on the island during the 1970s.
“Back then the locals thought it was only natural for so many butterflies to appear in winter,” he said. “They didn’t think it was important to conserve the valleys for the butterflies, and as a result their homes were gradually destroyed, with some valleys being turned into orchards.”
The threat to the butterflies became clear to Chan in 2000, when he participated in the filming of a documentary in the Maolin district of Kaohsiung City. “When the crew and I got there, the habitat was gone,” he recalled. “Instead, all we saw was a parking lot.”
To see what could be done to reverse the situation, a study on the ecology of the purple butterfly, with funding from the Forestry Bureau under the Council of Agriculture, was quickly set up. As a member of the project, Chan was invited to teach the locals how to better preserve the species.
His student Kuo Liang-huei, who married into the Rukai tribe, an indigenous group residing in Maolin, played a key role in protecting the butterflies. “She came up to me one day after class and said, ‘the Maolin people should protect the precious species themselves,’” Chan recalled. “It was as if she had a connection with the butterflies spiritually.”
Kuo soon put her ideas into practice. She taught the Rukai children about the purple butterfly, including its breeding and feeding habits. Gradually, even the adults became more willing to grow plants necessary for the survival of the insect.
“It is so important to have someone like Kuo spearheading the preservation efforts,” Chan said. “The locals often have trouble making ends meet, and have no time or energy for other issues irrelevant to themselves.”
In spite of all the efforts over the years to conserve the natural habitat of the purple butterfly, Chan pointed out that none of the goals he and the other researchers set out has been accomplished.
According to Chan, butterflies tend to gather where people prefer to live, thus humans are practically forcing the butterflies to find new homes.
Entomologists like Chan are also being forced to devise new strategies. “We are working on the possibility of human beings and butterflies coexisting,” he said. “For example, growing plants in parks or getting people to grow plants on their balconies or in their yards to attract butterflies.”
An additional threat to the butterflies, and to human beings as well, is global warming, which could cause extreme weather patterns to proliferate, according to Chan.
Chan cited as example, Typhoon Morakot of August 2009, the deadliest storm to strike Taiwan in more than half a century. It devastated many parts of Maolin, including the homes of the butterflies. “Once these natural habitats are destroyed, restoration is impossible,” Chan said.
“Damage to the global environment by human beings will affect the butterflies for years to come. All we can do is to try our best to maintain the habitats.”
To a researcher who has been fascinated by butterflies since childhood, conserving them is a pursuit that cannot be given up. “As long as more people recognize the importance of the issue and are willing to do what they can to help, there is hope for preserving the species.” (HZW)
Write to Grace Kuo at morningk@mail.gio.gov.tw