Purple Crow Butterflies are seen during the winter months around Dawu Mountain and Laonong River valley. The Taiwanese Purple Crow Butterflies and the Mexican Monarch Butterflies are the only two species of butterflies that migrate during the winter months. Therefore, butterfly researchers have named this regional unique phenomenon "Purple Crow Butterfly Valley". 
The best time to see the thousands of butterflies is from November to March from 8:30 am to 11 am, particularly if the previous day had been rainy. If visitors come before sunrise they can see the butterflies hanging on the tree branches, where they sleep. At dawn the butterflies awaken and appear to do what the Japanese call a phantom color dance, where millions of tiny hang-gliders fly down the valley in unison. When they stop for water it looks like a purple carpet along the river.
 The ecological factors of Maolin play a crucial role in providing the butterflies with a healthy environment. They feed off the region's trees and plants, so visitors must be aware of the regional ecology and how important it is to not touch or damage it when observing the butterflies. Maolin District Office has set up a butterfly trail, so visitors can observe the butterflies without damaging the ecology. The Tourism Bureau has also provided several information boards along the trail to educate visitors about the butterflies and the regional ecology. Even "flying butterfly" road signs put up around the area to remind drivers to slow down if they see the swarms of butterflies along the road. Maolin National Scenic Area is the only place in the world that has road signs for butterflies!.
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