Close interrelations between plants and animals have developed during evolution. One form of symbiosis is common in South America and Africa and is extremely fascinating: some flowering plants don't offer nectar or pollen, but a fatty oil. These flowers are called "oil flowers". This interrelation is hardly known in Europe although it occurs between bees (Macropis) and their host plant, the Yellow loosestrife (Lysimachia). The film was shot in their natural habitat at the banks of the Rhine backwaters. By means of macrography and slow-motion all phases of the bees' complex collecting behaviour are documented, including their nests. The flower structure is explained in detail. The film exemplarily introduces the basic mechanisms of a plant-animal interaction and the close connection between form and function in an ecosystem.