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Identification marks
Body 7–10 cm, tail 5–9 cm
The house mouse is evenly greyish-brown in colour; the belly is only a shade lighter than its back. Its head is round, its nose tapers, and its ears are big and 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 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.
Occurrence
Mice are excellent climbers, jumpers and swimmers. They are active in the evenings and at night. 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 pups every year. A house mouse prefers dry spaces.
House mice can eat very varied foods. In the wild, they feed 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.
Damage
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. You should ask the seller for more detailed instructions on how to use poisons. The most effective way to exterminate mice is to order a job from a specialist business.
The Environmental Health Unit monitors pest reports received from different parts of Helsinki and assesses the need for regulatory measures. If necessary, we inform property owners about the responsibility to exterminate mice. Measures are not usually performed based on individual mouse sightings.
Identification marks
Body 90–120 mm, tail 90–135 mm.
The yellow-necked wood mouse has a slender body. Its ears are large, its back is yellow-brown and its belly is white, and it has a long tail. The yellow-necked wood mouse is significantly larger than the house mouse. The forest mouse is also more colourful than the house mouse, especially as an adult. It does not have the pervasive mouse smell.
Occurrence
The yellow-necked wood mouse is native to Southern and Central Finland. It feeds on seeds, buds and larvae.
The yellow-necked wood mouse rarely settles in 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. Piles of seeds found in strange places in summer cabins that have been left cold during the winter are also usually stored there by the yellow-necked wood mouse. During the autumn especially, they prefer to move closer to residential buildings or their outbuildings.
Damage
Catching any diseases from a yellow-necked wood mouse is very unlikely. The yellow-necked wood mice that have moved indoors during the winter mostly look for their food in nature, but the scratching sounds they make in ceiling structures, may disturb those sleeping upstairs, for example. They may also dig around in insulation materials, but they do not usually cause damage by gnawing.
Identification marks
Body 11–29 cm, tail 8–23 cm.
The back of a common rat is dark or greyish-brown, and the colour of its belly ranges from light to grey. The tail is shorter than the body and light on the underside. The pups are clearly more robust than mice.
Occurrence
A rat likes to dig into the ground and prefers damp spaces. It also lives in sewers. Rats eat almost anything. Badly managed waste collection points and birdfeeders attract rats, and they may even feed on dog faeces.
A rat is a productive reproducer and gives birth to one litter every month. In a year, a female may produce 30 to 40 pups.
Damage
Rats cause damage by gnawing on anything softer than marble, even concrete. They eat and contaminate foodstuffs and fodder, damage packages and structures, cause general untidiness, and spread diseases and parasites.
Prevention and extermination
According to the Health Protection Act, the disposal of rats is the responsibility of the owner or holder of the property. If necessary, the City of Helsinki exterminates rats in parks or in its own properties, for example.
When exterminating rats, the most important thing is to prevent them obtaining food. Rats can also be repelled with mechanical instant-killing traps, for example. However, extermination is rather ineffective if the rats gain nutrition from places such as waste bins or bird feeding sites.
Extermination should be started if the rats cannot be removed by other means, and/or their nests have been detected in the property area. Extermination is most effective when it is carried out simultaneously in the areas of several properties. If you order an extermination from a professional, it is a good idea to discuss the matter with your neighbours. Rats cannot be poisoned by private individuals.
The Environmental Health Unit monitors pest reports received from different parts of Helsinki and assess the need for regulatory measures. If necessary, we inform property owners about the responsibility to exterminate rats. Measures are not usually performed based on individual rat sightings.
Occurrence
Finland has 11 known species of bats. Most of the species hibernate in Finland, although a few migrate to the south.
Damage and their prevention
Bats can hide in attics during the day. Bats living in the attic may also bring in common bed bugs, and their guano may cause odour problems.
The access of bats to the building can be blocked by obstructing their access routes Bats can crawl in through holes less than two centimetres wide. Their access holes are usually on the western and southern walls of the building. Access routes can also sometimes be found due to the staining around the hole or the guano underneath it.
Nearly all bats leave buildings during the night, which enables their access to be blocked while they are gone. Bats cannot be evicted between May and September.
Bats that come indoors in human residences are usually young individuals who have got lost. They will usually leave by themselves if a door or window is left open, and other exits are closed. Bats are not aggressive and do not attack, but they may bite if they are caught. Do not handle bats with your bare hands, as some may carry the rabies virus.
According to the Nature Conservation Act, bats are protected. They are also under the strong protection defined in appendix IV of the EU nature directive and are protected by several international agreements. If you are considering getting rid of bats in your building, you should first contact your regional Centre for Economic Development, Transport and the Environment, which will provide further instructions.
Identification marks
During the summer, squirrels are typically reddish-brown in colour. Their belly has a lighter spot. Their winter coat is greyish and includes ear tufts and a fluffier tail. Different colouring can be seen at times.
Occurrence
Squirrels have spread from coniferous forests to urban gardens and parks during the last century. Squirrels are also frequent suburban visitors, where they can climb walls and visit indoors as well.
Squirrels build their nests from twigs on tree branches, but nests can often be found in large birdhouses and buildings as well.
Damage
In residential communities, squirrels should not be fed without the permission of all the residents, or there may problems with neighbourly relations. After all, squirrels not only visit the balcony of the person feeding them but start visiting the neighbouring balconies as well. This may cause problems for people who want to lull their babies asleep outside, grow flowers on their balconies or just keep their balcony door open.
Squirrels do not cause a significant risk to hygiene, but they may damage the structures in wooden houses, especially heating insulation, or disturb the peace during the night. Open attics and roof triangles are typical places that may attract squirrels. Squirrels rarely gnaw undamaged healthy wood to make routes, but they may, however, make the ventilation gap between the wallboards and the ceiling bigger so that they can fit in.
Prevention and extermination
Access routes should be blocked between the late summer and early spring when the squirrel is away from the nest. If this is done during the late spring or at midsummer, the danger is that the pups will starve in the nest, as their mother will no longer have access to it. When blocking the route, remember to use sufficiently sturdy materials such as sheet metal or iron netting and mount them by screwing them in, for example. Squirrels can easily twist off chicken wire structures or flimsy nails.
Catching a squirrel, including catching it alive in a trap, requires a special permit from the Finnish Wildlife Agency in the first instance. This method is not even very effective, as other squirrels tend to quickly move into any appropriate places.
According to some observations, cat repellent sold in hardware stores may also work on squirrels. The bergamot oil-based solution has a pleasant scent to humans, so it can be tested on balconies or in attics where squirrels are unwelcome visitors.