THE DORMOUSE Muscardinus arvellanarius


Orange/yellow fur; the only small mammal with a thick bushy tail.
Head/body length: about 60-90mm, tail 57-68mm.
Weight: 10-15g in juveniles; 15-26g in adults; up to 43g before hibernation.

General Ecology:

The dormouse is a strictly nocturnal species, found in deciduous woodland and overgrown hedgerows. It spends most of its time climbing among tree branches in search of food, and rarely comes to the ground. It feeds on flowers, pollen, fruits, insects and nuts. During the day it sleeps in a nest, often in a hollow tree branch or a deserted bird nest or nestbox.

Dormice occur mainly in southern counties, especially in Devon, Somerset, Sussex and Kent. There are few recorded localities north of the Midlands, though they are present in parts of the Lake District and scattered in Welsh localities.

Dormice live at low population densities (one tenth as abundant as bank voles and woodmice in the same habitats). They can raise one or occasionally two litters a year, each usually of about four young. The new-born dormice remain with their mother for 6-8 weeks before becoming independent. The breeding season and success depends very much on the weather. Dormice are able to lower their body temperature and become torpid, so saving energy, if food is short or weather prevents them foraging. During the winter they hibernate and are not normally active again until about April or May. Thus dormice may spend three-quarters of their year "asleep", behaviour which earned them their sleepy reputation in Lewis Carroll's Adventures of Alice in Wonderland. Dormice live up to five years in the wild, much longer than other comparable small mammals.


Dormice are strictly protected by law and may not be intentionally killed, injured or disturbed in their nests, collected, trapped or sold except under licence. Their principal requirement is for a diverse habitat featuring several different trees and shrubs to provide food throughout the summer. Coppice management of woodlands can create such conditions; but cleared areas and wide rides may interfere with the movements of dormice, because the animals live almost exclusively in the trees. Surveys show that dormice have declined in Britain this century. Loss and fragmentation of ancient woodlands, climatic difficulties and suspension of coppicing are all probably connected with this. Nestboxes, put up with the entrance facing a tree trunk, are attractive to dormice and help survival and breeding success. Re-introductions of dormice are often suggested, but these require suitable (large) areas of woodland habitat and long periods of supplementary feeding. Breeding dormice in captivity is difficult and wild-caught animals are unlikely to be available in sufficient numbers. If fewer than 20 animals are released there is a high risk of failure.

Frequent Questions:

Where can I get a pair of dormice?
You cannot; dormice may not be trapped or sold except under licence from English Nature (Northminster House, Peterborough, PE1 1UA) or the Countryside Council for Wales (Plas Penrhos, Ffordd Penrhos, Bangor, Gwynedd LL57 2LQ) as appropriate.

Can we introduce some to our woods?
They may be there already. If they are not, then the habitat or climate may be unsuitable and introduction would probably result in their death.

Where can I go to see dormice?
Few zoos have them and in the wild they are almost impossible to see at night, but your County Wildlife Trust may have some in nestboxes.

Are there dormice in my local wood?
Dormice are small, secretive and nocturnal and so are unlikely to be seen except by accident. The best way to find out if they live in your area is to look for signs of their presence such as nests and remains of food. Dormice construct their own nests from shredded honeysuckle bark woven into a ball, which they often surround with layers of leaves. The result is a rather untidy, loosely woven structure the size of a grapefruit, without any definite entrance. These nests may be close to the ground, but have been found as high as 22 metres. Typical sites are low bramble bushes or thick undergrowth beneath trees with edible fruit such a hazel and sweet chestnut. Look for nests from autumn until late spring when there is no danger of disturbing breeding animals. Nibbled nuts can also be used to identify the presence of dormice. Small mammals have characteristic ways of opening hazel nuts. The hole in a nut opened by a dormouse, has a smooth inside surface with toothmarks around it on the shell surface. Further details of methods of surveying for dormice are given in A Practical Guide to Dormouse Conservation (see below), which also describes how to encourage dormice by putting up nestboxes in woodlands.

Further Information: