Although important roles of flood disturbance to terrestrial ecosystems adjacent to riverine ecosystems are well known, there still exits much uncertainty in response of terrestrial arthropods such as Hymenoptera which play important roles in ecosystem processes to events with an unprecedented magnitude under future climate change. This study examined flying Hymenoptera responses to a record-breaking flood in August 2016 in Eastern Hokkaido, and underlying mechanism from the perspectives of community structure. Change in abundance of flying Hymenoptera in riparian forests was determined before (2014) and after (2017, 2018) the flood. Community structure in different habitat types (riparian forests, interior forests and gravel bars with & without debris) was determined by individuals captured in 2018.Total abundance in riparian forests decreased significantly in 2017, and remained still lower in 2018 compared with the pre-flood level. Eight taxa significantly contributed to the differences in community structure among habitat types. Braconidae, Ichneumonidae, Proctotrupidae and Scelionidae, which were unique to interior forest, disproportionately increased from 2017 to 2018. Overall, the relatively slow recovery pattern from impacts of flood could be explained better by habitat preference of different taxa and lingering negative effects on gravel-bar habitats.