Yellow swarming fly
Yellow swarming flies are small, predominantly yellow-black flies, which are approximately 2 mm long and have 3 shiny black vertical stripes on their back. The larvae develop over the summer on meadows, fields and pastures, and are predators, living off root lice and gallicolous aphids.
The adult flies then often seek out buildings in the autumn and enter these to hibernate.
In this context, problems only arise when the adult flies appear en masse, as these can be an unpleasant household pest in the autumn. When the flies approach, suitable high, light buildings (high-rise buildings, church towers, etc.), which have often been used as a winter habitat for several generations, often appear to turn black due to the sheer amount of the insects. The creatures do not feed or reproduce in their hibernation hiding place.
When they approach in autumn, you should keep your windows closed or attach fly screens to prevent them from entering en masse.