作品は縦200cm×横100cmの3点組です。
雪が降りだす前の晩秋の夕暮れ時、ブナ林の中をひらひらと舞っているのはフユシャクという蛾の一種です。珍しい蛾ではなく、晩秋から冬にかけて、全国の雑木林で見られます。飛んでいるのは全てオスです。夜行性で、夕暮れ時になるとどこからともなく舞いだします。メスは翅が退化していてほぼ無く、落ち葉の下にいるのか、あまり見かけません。
フユシャクは、幼虫の頃はブナ科の木の葉を食べていますが、成虫になるとオスもメスも口が退化していてエサを食べません。それは、フユシャクが成虫になる季節はエサになるものが少ないのと、エサには水分がある為、この時期に水分を摂ると体が凍ってしまうからだと考えられます。
また、メスに翅が無いのは、体内の限られたエネルギーで子孫を残す為に、翅を無くし、その分のエネルギーを卵に向けたのではないかと考えられます。メスは飛ばない代わりにフェロモンを出してオスを導きます。
フユシャクが晩秋から冬にかけての夕暮れ時に活動するようになったのは、捕食圧による自然選択によると考えられています(Rydeii et al.,1997; Svensson et al.,1999; Tammaru et al.,2001)。捕食圧とは、ある種が、他の肉食動物に食べられることによって、生態環境が限定されていくことです。
夕暮れ時のブナ林で、触ると粉になってしまいそうな薄い羽根で舞う姿や、永い年月をかけて、子孫の為に口も翅も退化させる潔さを思うと、美しさと同時に怖さを感じ、もうすぐ冬だなと少し身構えするような気持になります。
参考文献
西浩孝(2008)第2部 松之山および柏崎市におけるフユシャク類の出現時期(途中経過),p45-52.
The work is a set of 3 pieces measuring 200cm long and 100cm wide.
Fluttering in the beech forest at dusk in late autumn, before the snow begins to fall, is a type of moth called a Fuyusyaku. It is not a rare moth, and can be found in thickets throughout Japan from late fall through winter. All of those flying are males. They are nocturnal, and at dusk they appear out of nowhere. Females are almost wingless, and are rarely seen, perhaps under fallen leaves.
As larvae, the Fuyusyaku feed on the leaves of beech trees, but as adults, both males and females have degenerated mouthparts and do not feed. This is thought to be because there is not much to feed on during the adult season, and because the food contains water, which would freeze their bodies if they ingest water at this time of the year.
It is also thought that the reason why the female has no wings is because she has to use the limited energy in her body to produce offspring, and she may be directing that energy to her eggs. Instead of flying, the female produces pheromones to guide the male.
It is believed that the Fuyusyaku become active at dusk in late fall and winter due to natural selection caused by predation pressure (Rydeii et al.,1997; Svensson et al.,1999; Tammaru et al.,2001). Predation pressure is the limitation of the ecological environment as a species is eaten by other predators.
When I think of the way they dance in the beech forest at dusk with their thin wings that seem to turn to powder when touched, and of the grace with which they have spent so many years degenerating their mouths and wings for the sake of their offspring, I feel a sense of fear as well as beauty, and I feel a little prepared for winter to be upon us soon.
References
Nishi, Hirotaka (2008) Part 2: Occurrence timing of Fuyusyaku species in Matsunoyama and Kashiwazaki City (in progress), p45-52.
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佐藤弘隆SATO Hirotaka
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