House mouse

(Mus musculus)

Body 70–100 mm, tail 55–95 mm

Identification marks

The house mouse is evenly greyish brown in colour, the belly is only a shade lighter than its back. Its head is round, nose tapering and the ears are big and located on the sides of the head. A young rat can be distinguished from a house mouse by its big back legs and large head.

House mouse. Photo: Martti Londen

House mouse excrement is usually black in colour, but may vary, due to the available sustenance. The round excrement is around 7 mm long, thin and sharp at the other end. Sometimes, there are piles of them.


Mice are excellent climbers, jumpers and swimmers. Their active day times are evenings and nights. They usually live in hiding places near a food source and build their nests in soft materials. The female may give birth to up to 40 cubs every year. A house mouse prefers dry spaces.

House mice can eat very varied foods. In the wild, it feeds on seeds, roots, other plant parts and insects. House mice living in residential buildings eat almost any food they can find. In particular, they like various seeds, but they also feed on soap, glue, candles and many other household goods.


A house mouse is a risk to hygiene in the kitchen, as it may spread various diseases when looking for food.

Prevention and extermination

Mouse poison can be placed in several spots in a five-metre radius. Traps intended specifically for mice need to be used for extermination.

Municipal health protection authorities may order the necessary measures in a municipality in order to exterminate pests, if they are thought to spread diseases or if they, otherwise, cause damage to health (763/94, Section 31).

Yellow-necked wood mouse

(Apodemus flavicollis)

Body 90–120 mm, tail 90–135 mm

Identification marks

Slender body, large ears. The back is yellow-brown and the belly is white. Long tail.


The yellow-necked wood mouse is native to Southern and Central Finland.

Yellow-necked wood mouse_vastavalo

The yellow-necked wood mouse rarely settles into residential buildings, but its night-time wanderings may take it indoors to look for sustenance or to store the food that it has found outside. Also, piles of seeds found in strange places in summer cabins that have been left cold during the winter are usually stored there by the yellow-necked wood mouse. During the autumn, in particular, they prefer to move closer to residential buildings or their outbuildings.

A yellow-necked wood mouse is an even better climber than the house mouse and is also able to find access to apartments. In the wild, it can also be found in a birdhouse.

The yellow-necked wood mouse feeds on seeds, buds and larvae. The yellow-necked wood mouse is clearly larger than the house mouse and it does not manage to creep into food cupboards as often. The yellow-necked wood mouse is also more colourful, especially as an adult. It does not have the pervasive mouse smell and it usually doesn’t cause any damage by gnawing on things.


It is very unlikely to catch any diseases from a yellow-necked wood mouse. The yellow-necked wood mice that have moved indoors during the winter mostly look for their food in the nature, but the scratching sounds they make, for example, in ceiling structures, may disturb those sleeping upstairs, and they may also dig around in the insulation materials.