There are three species (Corbet 1978; Corbet and Hill 1992; Harrison and Bates 1991; Kryštufek and Vohralik 1994; Mallon 1985; Nader 1989):
Holden (in Wilson and Reeder 1993) suggested that D. nitedula may actually comprise two or more species. She also included Chaetocauda (see account thereof) in Dryomys.
After Wilson and Reeder (1993) was published a third species was described:
Head and body length is 80-130 mm, tail length is 60-113 mm, and weight is 18-34 grams (Gaisler, Holas, and Homolka 1976; Ognev 1963; Van Den Brink 1968). The general coloration is grayish brown to yellowish brown on the upper parts and buffy white on the underparts. Dryomys is similar to Eliomys but is smaller, has a skull with much smaller tympanic bullae and a more rounded braincase, and has a more uniform tail, which is flattened and moderately bushy. Females have eight mammae.
Forest dormice inhabit dense forests and thickets at elevations of up to 3,500 meters; they sometimes utilize cultivated areas, gardens, and rocky meadows (Grzimek 1975). Their nests are usually located in dense shrubbery or the lower branches of trees. Hibernation sites may be in hollow trees, among tree roots, or in underground burrows. The temporary nest of an individual animal is rather flimsy, but natal nests are solidly constructed (Ognev 1963). Studies in Israel showed that nests are located 1-7 meters, usually about 3 meters, above the ground in the branches of trees. They are globular, measure 150-250 mm in diameter, have an outer layer of twigs and leaves and an inner lining of bark or moss fragments, and have an entrance hole on the side or top (Harrison 1972).
Forest dormice are nocturnal and arboreal. They climb with great agility, and their leaps from branch to branch cover up to 2 meters. In Israel they are active year-round, even in the high mountains, though they may undergo torper for some hours each day during the winter (Harrison 1972). Farther north the data are conflicting. Evidently, hibernation sometimes occurs from October to April in Europe. During this period the animal curls up like a ball while sitting on its hind legs; it wraps its tail around its body and presses its hands onto its cheeks. The animals may occasionally emerge to eat from stores of food. Observations in Russia, however, suggest that extensive, deep hibernation does not necessarily occur and that forest dormice may be active throughout most or all of the winter (Ognev 1963). The diet of Dryomys consists of seeds, acorns, buds, fruits, arthropods, eggs, and young birds; animal matter seems to be preferred during the summer (Grzimek 1975).
Nests tend to be clustered in small groups in the same tree or adjacent trees (Harrison 1972). In one area of about 8,000 sq meters 11 inhabited nests were found (Ognev 1963). Dryomys has a variety of vocalizations, most notably a delicate, melodious squeak that serves as an alarm call. The breeding season extends from March to December in Israel, where each female gives birth two or three times annually, and from May to August in Europe, where there usually seems to be just a single litter per year (Gaisler, Holas, and Homolka 1976; Grzimek 1975; Harrison 1972; Ognev 1963). Gestation periods of 21-30 days have been reported (Hayssen, Van Tienhoven, and Van Tienhoven 1993). There are usually two to five, occasionally as many as seven, young. The young weigh about 2 grams at birth, open their eyes at 16 days, and attain independence after 4-5 weeks. In Europe they do not mate until after their first winter.
Forest dormice are quite aggressive and never really become tame in captivity. They may reach a point at which they will allow themselves to be petted, but they usually bite with their sharp incisors when an attempt is made to hold them. If disturbed while resting, they often lie on their back or side and scratch with their hind legs. If disturbed further, they may suddenly leap high into the air and spit and hiss. Wild populations sometimes cause local damage by raiding fruit orchards and gnawing the bark of coniferous trees.
Pucek (1989) reported that because of the destruction of forest habitat D. nitedula is regarded as endangered in the Czech Republic and rare in most other European countries. Nader (1989) designated D. laniger as rare. The IUCN now designates both species as near threatened.
Information taken from: Nowak, R.M. (Ed.). Walker's Mammals of the World. 6th Edition. The John Hopkins University Press. Baltimore and London, 1999.