Nasu in Summer
Trees are scarce high in the Nasu mountains, but summer brings plenty of new growth to their slopes. Flowers appear on Mt. Chausu (1,915 m) in mid-June, among them the Japanese azalea, birchleaf spirea, and the bell-shaped, bright-pink blossoms of urajiroyōraku (Menziesia multiflora). A relative of European edelweiss called usuyukisō blooms in July and August; its name means “plant of light snowfall” because the white upper leaves look as if they are dusted with snow. Among the birds living on the Nasu peaks are Asian house martins, alpine accentors, and Pacific swifts.
Visitors to the Numappara Marshland in late June to mid-July will find the wetland dyed yellow by the blooming Amur daylilies. By early July, the deep violet petals of wild Japanese irises appear, followed by lacy pink clusters of akabana-shimotsuke-sō, a variety of meadowsweet that is limited to mountainous areas in central Honshu.
In the lowlands, Latham’s snipes, brown-headed thrushes, and fan-tailed warblers call to one another. Though seldom seen, several snake species inhabit Nasu: the Japanese striped snake, Japanese rat snake, tiger keelback, and Japanese pit viper. The latter two species are venomous, but the keelback is extremely shy, and the pit viper is found only in a limited area in the north of Nasu. Hikers should avoid going barefoot, even if encounters with snakes are rare.
Development, pollution, and pesticides threaten fireflies on a global scale, but several species still inhabit the clean waterways of Nasu. The Genji firefly, the smaller Heike firefly, and the obabotaru (Lucidina biplagiata) light up the summer nights.
Many varieties of mushrooms—such as oyster mushrooms, late oyster mushrooms, and honey fungus—are found in ravines and along the Yosasa River. Another species, the “moonlight mushroom” (tsukiyotake), glows faintly green in the dark. Although it closely resembles the edible oyster mushroom, the tsukiyotake is poisonous.