We used the Swiss Canopy Crane near Basel, Switzerland, to sample 13 mature oaks within a natural temperate forest before (July 2000) and after (July 2001, July 2002) the beginning of canopy CO₂ enrichment in September 2000. We counted and identified galls and mines on the 50 terminal leaves of three randomly chosen branches at random positions in the lower (<10m), middle (10-20m), upper (20-30m) and top part (>30m) of the canopy yielding a total of 6000 checked leaves per year, and determined the change of proportion of counts on enriched and non-enriched trees. The most dominant gall-former, the cynipid wasp Neuroterus quercusbaccarum, showed a significant increase of proportion on CO₂ enriched trees. This is in striking contrast to the response of insect herbivores in the published literature. Also the close relative cynipid, N. numismalis, and the mining moth Tischeria ekebladella did not show any decrease; their proportion on enriched and non-enriched oaks did not change after the onset of CO₂ enrichment.