||Overwintering larva in its pergamentous whitish case. If opened (case), dark brown caterpillar with shiny black head is found inside. Larva feeds with the bud interior almost completely boring inside the still closed bud. Overwintering loci are always on twigs in sheltered crevices near the buds. Case grows as larva gets bigger and after the pupation moths emerge in late spring - summer. Common pest sometimes causing mild damages on pedunculate oak (Quercus robur) stands in Croatia.