In the 1950s and '60s, Taiwan's butterflies were netted and bagged for export in the tens of millions (per year!). Remarkably, only three species became extinct, though numbers plummeted for decades. These days top butterfly areas are well protected, and these delightful creatures can be seen everywhere year-round.

Taiwan has over 400 species of butterflies, of which about 60 are endemic. Some standouts include the blue admirals, red-base Jezebels and Magellan's iridescent birdwing, which has one of the largest wingspans in the world. Prominent sites include Yangmingshan National Park's Datunshan, where chestnut tigers swarm in late spring; the overwintering purple butterfly valleys in the south; Fuyuan Forest Recreational Area; and the Yellow Butterfly Valley outside Meinong. You can also see butterflies in Linnei, Maolin and Tatajia.

On Wings of Gossamer: Butterfly Migration

Butterfly migration is fairly common the world over, but Taiwan's purple crow migration can hold its own. Each year in the autumn, as the weather cools, bands of shimmering purples (four species of Euploea, also known as milkweed butterflies) leave their mountain homes in north and central Taiwan and begin to gather in larger and larger bands as they fly south. By November they have travelled several hundred kilometres, and in a series of 12 to 15 warm, sheltered valleys in the Dawu Mountain Range, 10 to 15 million of them settle in for the winter.

This mass overwintering is not common. In fact, Taiwan is one of only two places in the world where it happens: the other is in the monarch butterfly valleys of Mexico. The most famous overwintering site in Taiwan is in Maolin Recreation Area, but according to experts this is actually the least populated valley. It simply had the advantage of being the first to be discovered and written about.

The discovery happened in 1971 when an amateur entomologist was invited into Maolin by local Rukai people. Though not aware of just how significant the find was, the entomologist (and others) continued to study the valley. By the mid-1980s it was obvious that a north–south migration route existed, though it wasn't until 2005 that the 400km route along the west could be roughly mapped out. Since then a second migration path along the east coast and a connecting path joining the two have also been discovered.

The northern migration usually begins around March, and, astonishingly, it involves many of the same individuals who flew down in the autumn (purples have been found to live up to nine months). Some good places to spot the spring migration are Linnei, Dawu (in Taitung County), Pingtung County Rd 199, Taichung's Metropolitan Park, Baguashan and coastal areas of Jhunan (Miaoli County) where the purples stop to breed. In May and June, large numbers of purples appear to take a mysterious detour and are blown back south over the high mountain pass at Tatajia.

If you're curious as to just how the migration occurs in the first place, the answer is relatively simple: seasonal winds. In the autumn they come strong out of Mongolia and China, while in the spring they blow up from the Philippines. Without them the purples would be unlikely to move such great distances and this would mean their death when the temperatures drop during northern winters.

From spring until autumn, purple butterflies are easily spotted all over Taiwan. So give a nod to these brave wayfarers when you encounter them in a park or mountain trail. They may have come a long way.

For a mostly accurate look at the discovery of the western migratory route, check out The Butterfly Code, a Discovery Channel DVD.