October 29, 2017
Adorable butterflies live mysterious life on long migrating journey from Japan
Migrating creatures are not limited to birds, animals and fish. A kind of spotted butterflies, called "asagimadara" in Japanese, spend the summer in cool areas, mainly on highlands, in northern Japan and fly over the sea to southern Japan regions or Taiwan from late autumn to breed the next generation.
Chestnut tiger butterflies, so called in English, have pretty spotted wing patterns. The front wings, 4 to 6 centimeters in length, have semitransparent pale blue spots, while the rear wings are red or red-brown. When the wings are expanded, they are about 10 centimeters long.
The fact that asagimadara butterflies migrate from Japan to southern regions in autumn and fly back to Japan in spring in the following year came to be known through marking researches by groups of citizens in many parts of Japan since the 1980s.Early researches revealed some asagimadara flew 1,000 to 1,500 kilometers from the northern and central Japan regions to the Nansei Islands, including Okinawa, but their migrating journey record was renewed almost every year later.
The current longest record, 2,246 kilometers, was reported in 2006, when a female asagimadara released with markings along with others in Yamagata Prefecture, northern Japan, in August, was found on an island near Taiwan three months later.
Researches joined by citizens have revealed their behaviors and flying routes, both northward and southward, but many parts of their life remain mysterious.Why can they fly so long a distance? How do they feed themselves while flying across the sea? and where do they sleep at night?
The life of spotted butterflies, such as asagimadara, is about four months. This means that the asagimadara butterflies which fly southward from Japan and those which fly northward to Japan in the following year are not the same ones. They are all almost newly born when they start migrating, but they realize the timing of migration and the direction of migration. How?The one can sometimes see asagimadara with their wings worn out. "It is just natural. Their wings get worn out, because they travel so long a distance," says a butterfly watcher living in southwestern Japan.
Many asakimadara are seen sucking nectar from certain kinds of flowers while in Japan in summer or on their way to southern regions in autumn.In the southwestern Japan region of Kyushu, they are often found flying around thoroughwort flowers, called Fujibakama in Japanese, which is known as one of the "nanakusa" seven flowers of autumn.
The nectar of the flower has a toxic agent. The fact that they seek nectar from Fujibakama flowers is taken to mean that they protect themselves from insects or birds by obtaining the toxic nectar.Recent studies show that the northern limit of their summer habitats is going up to the north. The timing of migration to their summer or winter habitats is said to be changing in recent years. These indications are taken as signs of the global warming.
"The tiny creature (asakimadara butterfly) "tells us what's happening in the natural environment surrounding us," said a person who is familiar with their habits. "They are just adorable, and we must be even friendlier with them."
