Saperda populnea - Gall inhabited by earwig
Gall with exit hole in twig of a Poplar tree (Populus sp.) caused by larva of Saperda populnea.
If you look closely, you can see that the empty gall is now used as a shelter by a female European Earwig (Forficula auricularia) :o)
Another gall and exit hole on the same tree:
A couple of Saperda populnea found on the same tree: