Diplolepis rosae; Rosa canina
Gall wasps lay their eggs into the rose hips. Up to 60 eggs can be laid in one of these branches. After that some unopened leaves or buds create these buildings out of the plant. The ones shown here are old ones and allready empty. The wasps have allready emerged. They do that normally from May to August, but the galls stay on the plant.
Found on the hills surrounding my home village. They are very common here.