cynips quercusfolii known as gall wasp, round ball gall underside of common oak leaf quercus robur. inside is bug larva.

acorn apple attached autumn ball branch bug closeup common cynips europe european focus foliage forest fresh gall garden green home infected insect inside larva leaf leaves natural nature nest oak organic outdoors parasite plant quercus quercusfolii robur round season seasonal selective showing sphere stuck tree wasp wasps weird wild wildlife woods