The single species, G. japonicus, is found on the Japanese islands of Honshu, Shikoku, and Kyushu (Corbet 1978).
Head and body length is 65-80 mm and tail length is 40-55 mm. Weight is 14-40 grams (Ishii 1994). The coloration is pale olive brown with a dark brown to black dorsal stripe. This stripe varies in width and sometimes is very obscure. The fur is soft and thick. A tuft of long hairs lies in front of the ear, and the tail is flattened from top to bottom.
This dormouse inhabits mountain forests, usually from about 400 to 1,800 meters in elevation; one individual, however, was captured in a cottage at 2,900 meters. Glirulus is arboreal and nocturnal. It shelters in a tree hollow or in a nest among branches. The round nest is covered on the outside with lichens and lined on the inside with bark. Winter hibernation is spent in hollow trees, cottages, or birdhouses. A semidormant individual was once captured in July in a snow depression in a ravine of the Japanese Alps, but after several minutes it awakened and escaped from the container where it had been placed. The diet of Glirulus consists of seeds, fruits, insects, and birds' eggs. In captivity it does well on rice, peanuts, sweet potatoes, fruits, and insects.
The young are usually born in June or July. Occasional births in October probably represent the second litters of certain females. There may rarely be as many as seven young, but observations of captives by Michi Nomura (Oiso-Machi, Kanagawa Prefecture, Japan, pers. comm.) indicate the usual range to be three to five and the average to be four; she also determined the gestation period to be about 1 month.
Wang, Zheng, and Kobayashi (1989) indicated that the number of Glirulus is very small and that the genus is legally protected. It evidently has declined mainly through loss of forest habitat. The IUCN now classifies it as endangered, noting that the decline has been at least 50 percent in the last 10 years.
Information taken from: Nowak, R.M. (Ed.). Walker's Mammals of the World. 6th Edition. The John Hopkins University Press. Baltimore and London, 1999.