Silverfish feel most at home in warm, damp and dark hiding places. That is why they are often found in bathrooms, laundry rooms, cellars or kitchens. Silverfish are nocturnal, so they usually cannot be seen during the day. They hide in small niches, cracks or between the floor tiles. Silverfish are not harmful as such, but if their numbers get out of hand, they can become a real plague.

A few silverfish in your flat do not yet constitute a defect. Several regional courts (Landgerichte) have ruled that an occasional appearance sometimes cannot be prevented. However, a defect may exist if the presence of a few silverfish turns into a full-blown infestation. How many silverfish amount to an infestation and how many rooms must be affected cannot be stated as a general rule. This has to be decided on a case-by-case basis.

It is important to note that the mere presence of these small creatures does not pose a health risk. In the case of an infestation, however, it can be assumed to be a nuisance. Courts have already deemed rent reductions of up to 20 percent permissible. In one specific case, a tenant had to spread poison in his bedroom himself to get rid of the silverfish and was allowed to reduce his rent by 20 percent. Other cases may also justify a reduction, but should always be assessed professionally.

Infestations of spiders and ants, especially in flats close to ground level such as ground-floor flats, are regarded as customary for the location, as they are among the unavoidable circumstances of this living situation, so a rent reduction is generally not justified. In most cases, spiders and ants are not hazardous to health. Quite the opposite, in fact: they feed on refuse or other pests and are therefore regarded as helpers in our latitudes.

A defect can only be said to exist in particularly extreme cases of infestation. In addition, the infestation must not be attributable to the tenant's own misconduct. In that case, a rent reduction is ruled out. When an infestation is serious enough to justify a reduction must again be decided on a case-by-case basis.

Larger animals such as rats and mice can seriously impair living comfort. Because of the noise they make, their behaviour in the flat and the potential transmission of diseases, these rodents generally constitute a rental defect. However, the tenant's place of residence must be taken into account in the assessment. In the countryside, mice are more to be expected than in the city. In the city, an infestation of mice and rats is much easier to prevent than in a natural environment.

But even in the city, a house mouse can turn up once without this directly constituting a rental defect. Only when a significant number of rodents are discovered is there a defect that decisively reduces the quality of living. Rats and mice can also appear in the city unimpressed by protective measures and find their way into the flat. Unfortunately, it is not possible to prevent this 100 percent.

Nests of wasps, hornets and bees in or on the flat are not only a nuisance but can also be dangerous. A rent reduction in such cases does not solve the problem, but it does put pressure on the landlord to remedy the defect.

However, not every nest constitutes an actual impairment. If the nests are abandoned or it is winter, the quality of living is not affected. A rent reduction is not possible in this case.

If the nests are inhabited, however, they are dangerous or even life-threatening, especially for allergy sufferers. What matters for tenants' rights is that the animals impair the use of the rented flat for a certain period of time and that the tenant cannot reasonably be expected to put up with it. However, the tenant cannot demand permanent protection from the landlord, as these small insects are part of living alongside nature. A defect therefore only exists if the unreasonableness is proven or the danger goes beyond the normal level. Here, too, an examination of the individual case is decisive.