Moths in winter

Dec.21,2001. M.Sekine

A fuyu-shaku moth

Colorful and graceful butterflies are among the most widely appreciated insects. While their relatives the moths fare poorly in popularity contests, butterflies may win out handily in popularity but, in terms of evolutionary success, it is the moths that come out squarely on top. The number of species of moths is ten or more times those of the butterfly. Actually, about 240 species of butterflies inhabit Japan, while the number of species of moths is at least 3,000, and probably much more.
Some 20 species of fuyu-shaku moths (literally, "winter-measuring-worm moths") have been recorded throughout Japan. These are the only moths known to appear in winter. Fuyu-shaku moths emerge only once a year, in winter, from their cocoons in the ground. Curiously enough, they have no mouth-parts. Therefore, fuyu-shaku moths don't take in food in adult stage. The most common species is kurosuji-fuyu-edashaku (literally, "black-striped-winter-cankerworm moth"), belonging to the family Geometridae. Their scientific name is Erannis obliquaria.
It is fascinating to see a flight of 30-odd male adult moths flit over fallen leaves in coppices in the daytime from late autumn through early winter. They search for the females. The female adults, however, are wingless. Perhaps, they adapt themselves to severe winters by losing their wings and by not eating at all.
As insects go, they are the stars of the winter. I'm deeply impressed by their intriguing physical and behavioral characteristics as described above.
Just one more thing, the spider, Labulla contortipes, belonging to the family Linyphiidae also matures in winter. Perhaps, this spider emits components of the moth-prey species' sex pheromones, imitating a chemical, to lure the male fuyu-shaku moths. Nature is becoming full of surprise.

A flight of male adult fuyu-shaku moths