has a very closed flower and the bumblebee on the picture needs to put a lot of effort into opening the petals. This slightly prude posture is due to the fact that it has developed a very close relationship with some flies belonging to the genus Chiastocheta.

These flies are entirely dependent on the Trollius europaeus and because of that also the most important pollinators of this plant. The adult flies spend most of their life inside the flowers.