The Apollo butterfly is one of the rarest butterfly species in Europe. It lives mainly in mountainous, rocky terrain. Largely as a result of humans' impact on nature, the Apollo is an endangered species, and it has been protected since 1936.

At the foothills of the Swabian Jura, where the butterfly thrives on a railway embankment built back in the 1930s, Deutsche Bahn has selectively cleared vegetation, enabling the small population to grow. In this way, DB is helping to preserve the species at this only permanently inhabited refuge of the Apollo butterfly in Baden-Württemberg.