Taiwan Today

Slowing down for butterflies speeds their conservation

Taiwan may be the only country in the world where the Ministry of Transportation and Communications (MOTC) has responsibility for butterfly conservation. This unique situation arose due to an extraordinary phenomenon: a 200-kilometer butterfly migration by four species of purple crow butterflies that takes place twice a year. They fly down the length of the island from north to south and back again, during which up to 200,000 of the insects flutter across the freeway.

The unusual task is the responsibility of the Freeway Bureau (FB) because the northward leg crosses National Freeway 3’s Linnei section in central Taiwan’s Yunlin County around Tomb Sweeping Day, a national public holiday that sees heavy traffic. The festival coincides with the rise of the seasonal southerly wind that the butterflies ride as daylight hours lengthen and temperatures rise. Since 2007 the FB has implemented measures to protect the butterflies in line with research from the Taiwan Purple Crow Butterfly Ecological Preservation Association (TPCBEPA). Huang Hsiao-wei (黃筱瑋), deputy director of the engineering department at the FB’s Taichung Area Maintenance Engineering Branch, explained the three main protective schemes put in place for the migration.

“One of our boldest measures is freeway lane closure,” Huang said. It comes into effect when the butterfly count, conducted manually by FB staff at a monitoring station on a northbound section of National Freeway 3, reaches 250 per minute. The swarms generally happen before the warmest part of the day, as the butterflies take flight in the morning, then rest and feed in the afternoon.

The second initiative, linked to observation of the butterfly’s treetop flight habits, is extensive planting of native tree species to form a continuous line along the freeway embankment. The 50 or more shrubs—laurel, flamegold rain tree, chinaberry, neem and soapberry—planted back in 2007 are now mature and others have been added, with around 250 currently bordering the Linnei freeway section.

The third protection the FB adopts during the northerly migration is to put up netting fences along the sides of the freeway. Standing 4 meters tall, the barriers ensure the insects fly high enough to avoid the cyclonic air movement generated by vehicles. This combines with the first measure to create a safer environment not just for butterflies, but also for drivers who could be distracted by the fluttering clouds of insects.

Macro View

Arresting as the sight of hundreds of butterflies on the move may be, their extraordinary resilience is best appreciated when examining them up close. The ideal time to do this is in the winter months in the south of Taiwan. When the northeast monsoon prevails around October and the northern part of the island becomes cooler, the butterflies migrate south to the warm humid valleys of southern Taiwan’s Kaohsiung City, Tainan City and Pingtung County, with the largest numbers congregating in December and January. They seek out southerly facing valleys at altitudes below 500 meters that are surrounded by forest and feature dry creeks. The most accessible site to see the butterflies in large numbers is in Maolin National Scenic Area, overseen by the MOTC Tourism Administration.

Purple crow butterflies, of the genus Euploea, are not spectacular at first glance given their medium size and dark appearance. However, iridescent hues within their wings are revealed in flight and bright sunlight, rendering their appearance especially striking. Blues, purples and greens are the result of light being reflected and bent by the nanostructure of scales on the wings. This subtle surprise revealed in motion, together with their long migration, is part of the mystique that has turned the butterfly into an iconic conservation symbol.

Remote Maolin

Maolin District suffered severe damage in 2009, when Typhoon Morakot washed away all but one of the bridges. In the decades since, new infrastructure projects have reestablished full access to the area. The new Maolin Visitor Center, opened in August 2024, is decorated with local artist Ubake’s beautiful detailed reliefs inspired by Indigenous Rukai culture. A short walk from the visitor center lies a small tree-shaded plaza, and zigzagging up the hill behind it is the 2.1 kilometer Zishalishali trail populated by shifting swarms of butterflies.

After three years of research in Maolin, the first dedicated conservation area was set up in 2014, and since then activities have been further refined and facilities upgraded. A two-day celebration took place in mid-November 2024 to herald the start of the autumn butterfly arrival. Lepidopterist Liaw Jan-Shan (廖金山), who plays a pivotal role in protecting the butterflies and their habitat in his position as TPCBEPA director, explained that Euploea butterflies have always wintered in Maolin in significant numbers, and many other species are present there all year round. Habitat work along the trail takes place over late summer and early autumn to plant and nurture food sources including ficus, tropical holly, verbena and milkweed in advance of the butterflies’ return. This encourages a part of the migrating population to rest and breed there, rather than carry on further south. Liaw explained that like many other migratory species, butterflies recognize their place of origin and return to the same food plant that nurtured them as caterpillars to lay their eggs.

The opening celebration was delayed by eight days due to a severe typhoon, and Liaw noted that many eggs and caterpillars had been washed away. However, the resilience of the creatures was evident as he displayed tiny spherical eggs—far less than a millimeter wide— on new ficus leaves. The larvae hatch after about four days and eat the fresh leaves. Each of the four species of Euploea caterpillars are different and as beautiful as the butterflies they will become. They sport bold stripes in black with yellow or orange and jaunty horn-like protrusions at head and tail to confuse predators. “Any bird that snacks on either the caterpillars or butterflies may feel slightly drunk,” Liaw said. “The larvae feed on trees that contain toxic alkaloids, which build up in their bodies and remain there through metamorphosis, rendering the insects mildly poisonous as prey.”

Sharing Wonder

During the opening weekend Liaw and other volunteers showed eggs and caterpillars displayed on potted shrubs, and butterflies within a net hide, to visitors to teach them to identify what species to look for along the trail. With a soft net, a swift motion and a nontoxic marker, Liaw demonstrated the first step in tracking butterfly migration routes and lifespan, lightly marking the letters ML for Maolin and 1124 for the date on the outside of the insect’s lower wing. Through a decade of such surveys, researchers have discovered that purple crow butterflies can live six to eight months, one of the longest lifespans among lepidoptera.

Liaw was tireless in answering questions from adults and children alike and revealed some surprising facts about the private life of the butterfly. Males in the genus Euploea have exuberant secondary sex characteristics that produce scent. Liaw again deftly wielded a net and conjured a male butterfly adorned with vivid yellow feathery brushes at its tail that pulse open and closed. He held it gently and wafted a scent as rich as a floral essential oil, redolent of the nectar it lives on, towards onlookers’ nostrils. Another species gave off a fresh woody scent as alluring as perfume. The rapt expressions of visitors is evidence of the importance of outreach and education on conservation issues. Anyone who has witnessed the improbably tiny eggs, seen iridescent wings in sunlight and smelled the scent of a butterfly will surely be happy to slow down their vehicle to ensure the insects’ survival.

“The MOTC has placed a strong emphasis on implementing green infrastructure and environmental restoration plans for national freeways in recent years,” Huang explained. “We are a potent force for conservation in Taiwan.” The ministry conducts inventory and analysis of roadside vegetation and roadkill and compiles ecological databases. In addition to the purple crow butterfly, it undertakes conservation measures for land crabs, leopard cats and pangolins, respecting input from ecologists and zoologists while coordinating across jurisdictions and agencies to achieve positive outcomes. The innovative role of this government body’s commitment to the issue of butterfly migration, combined with the work of lepidopterists and conservationists, is vital to the butterfly’s continued existence.

Write to Nai Li at mhchung@mofa.gov.tw