dormouse, name for Old World nocturnal rodents of the family Gliridae. There are many dormouse species, classified in several genera. Many resemble small squirrels. Dormice sleep deeply during the day, and European species hibernate for nearly six months of the year; their name is derived from the French dormir, "to sleep." Best known is the common dormouse, or hazelmouse, Muscardinus avellanarius, of Europe and W Asia, which resembles a mouse with a bushy tail. It is up to 4 in. (10 cm) long excluding the 2-in. (5-cm) tail, with rounded ears, large eyes, and thick, soft, reddish brown fur. Social animals, hazelmice build neighboring nests of leaves and grasses in bushes and thickets. They feed on insects, berries, seeds, and nuts, and are especially partial to hazelnuts. The European, or fat, dormouse, Glis glis, is the largest of the family reaching a length of 8 in. (20 cm) excluding the tail; it has a very thick coat of grayish fur and becomes extremely fat in autumn. It is found in forested regions of Europe and W Asia and lives in hollow trees. The ancient Romans raised it in captivity for food. There are many dormouse species in Africa. The spiny dormice of S Asia belong to a different rodent family, the Platacanthomyidae; they have spines mixed with their fur. The desert dormouse ( Selevinia betpakolalensis ) is placed in its own family, Seleviniidae. True dormice are classified in the phylum Chordata, subphylum Vertebrata, class Mammalia, order Rodentia, family Gliridae.