We conducted field surveys for trophobiotic Hemiptera Hemiptera and tending ants at 300 plots and over 12,000 trees at the BEF-China Main Experiment. Depending on tree species identity and sampling year, tree height was between 1 and 6 m. We selected 150 plots at each of the two experimental sites (‘site A’ and ‘site B’) representing each tree species at similar proportions across all tree species richness levels. Each site was surveyed three times for the presence of Hemiptera and interacting ants (trophobiosis), site A once in 2011, site B once in 2013 and both sites twice in 2014. To avoid effects of neighbouring plots and edge-effects, our surveys used a ‘core area’ approach on the central tree individuals guaranteeing a minimum buffer distance of 5.16 m to the adjacent plot margin. The number of plots available for sampling decreased with increasing tree species richness. To sample the same number of tree individuals for each tree species in each tree species richness level, we increased the number of trees sampled per plot with increasing tree species richness, from 36 trees in monocultures to 144 trees in 24 species mixtures. At each tree individual, a total of 20 leaves from three branch sections and their bark were visually inspected for the presence of Hemiptera and interacting ants. Ants were only considered as interacting when direct tending behaviour, such as honeydew excretion in response to ant antennation or the presence of ant constructed sheetings, was observed. Each unique trophobiosis between one ant species and one Hemiptera species per leaf or bark section was defined as one interaction, regardless of the number of interaction partners involved.