Common rat

(Rattus norvegicus)

Body 110–290 mm, tail 85–230 mm

Identification marks

The back of a common rat is dark or grey-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 cubs are, clearly, more robust than mice.


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, the female may produce 30 to 40 cubs.


Rats cause damage by gnawing on anything softer than marble, even concrete. It eats and contaminates food stuffs and fodder, damages packages and structures, causes general untidiness and spreads diseases and parasites.

Prevention and extermination

If you observe rats, you should first contact the owner of the plot or the building manager, or health inspector, if necessary. If you see rats in the parks and on the streets of Helsinki, you can also report your sightings to the customer service of the Urban Environment Division.

When a rat extermination is carried out, a warning sign should be placed in the area. Use of a bait box is recommended. It should be open on both ends and, if used outside, be made of a material that tolerates the dampness. Rats are very careful and it may take days before it takes the bait. Extermination should be continued, until the baits are left untouched.

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).