Dormice are small, nocturnal rodents belonging to the family Gliridae, a group distinct from both true mice and squirrels. These agile creatures are found across parts of Europe, Asia, and Africa, where they primarily inhabit forested and scrub environments. They are perhaps best known for their extended periods of inactivity, a characteristic reflected in their name, which is derived from a word meaning “to sleep.”
Physical Characteristics and Taxonomy
Dormice exhibit a morphology that gives them a resemblance to both mice and small squirrels. They are generally compact, with body lengths ranging from about 6 to 19 centimeters, and they are covered in soft, thick fur that can vary in color from golden-brown to gray. Many species possess a long, bushy tail, which is an adaptation that aids in balance as they navigate the canopy.
Their large, dark eyes are a distinguishing feature, specialized for maximizing light absorption to support their strictly nocturnal lifestyle. A remarkable defensive trait found in many dormice is “false autotomy,” the ability to shed the skin of their tail if they are grabbed by a predator. Taxonomically, dormice fall under the Order Rodentia and Family Gliridae, placing them separately from the Muridae family (true mice and rats) and the Sciuridae family (squirrels and chipmunks).
The Long Sleep: Hibernation and Torpor
The defining characteristic of dormice is their period of dormancy, which can last for six months or more in temperate climates, sometimes earning them the nickname “seven sleepers.” This extended state is a true hibernation, a major physiological shutdown necessary to survive the winter’s low temperatures and lack of food availability. The Edible Dormouse (Glis glis) has even been recorded hibernating for an astonishing 11.4 months in a single cycle.
During hibernation, the dormouse’s metabolic rate plummets dramatically to conserve energy, with the heart rate slowing and body temperature dropping to near ambient levels. They prepare for this process by actively foraging in the autumn to double their body weight, accumulating the fat reserves needed to sustain them throughout the winter. Individuals will lose up to 50% of their body mass by the time they emerge, often in late April or May.
This deep winter sleep is distinct from torpor, which is a shorter, temporary energy-saving state. Dormice may enter torpor on a daily basis, or during brief cold or wet spells in the spring and summer when food is temporarily scarce. Torpor allows them to reduce their energy expenditure until foraging conditions improve.
Ecological Niche: Habitat and Diet
Dormice are primarily arboreal, meaning they spend the majority of their active lives in trees and shrubs. Their preferred habitats are those that provide dense, interconnected vegetation, such as mature deciduous woodlands, layered scrub, and overgrown hedgerows. This structure allows them to travel safely through the canopy without exposure to ground predators.
Their diet is highly flexible and omnivorous, changing seasonally to take advantage of available high-energy resources. In spring, they consume protein-rich items like insects, flowers, nectar, and pollen from species such as hawthorn and honeysuckle. Summer and autumn foraging shifts focus to calorie-dense foods, including berries, fruits, and nuts. A clear sign of a dormouse feeding is the characteristic smooth, circular hole they gnaw into the shell of a hazelnut.
Conservation Status and Major Species
The dormouse family comprises nearly 30 species. The Hazel Dormouse (Muscardinus avellanarius), native to much of Europe, is a species of particular concern, with populations declining significantly due to habitat fragmentation and loss of traditional woodland management like coppicing. This habitat loss breaks the vital tree-level connections they rely on, isolating small populations.
The Edible Dormouse (Glis glis), also known as the Fat Dormouse, is one of the largest species, reaching nearly the size of a small squirrel. Another notable species is the Garden Dormouse (Eliomys quercinus), found across Europe and North Africa, noted for its distinctive black mask. Climate change poses an additional threat by disrupting their hibernation cycle, causing them to wake early when necessary food sources have not yet become available.