A field survey of ground beetle assemblages (Carabidae and Brachinidae) using unbaited pitfall trapping was carried out in the riverbed of the Yodo River, which runs through the north of Osaka Prefecture and has such characteristic landscapes as a reed community at Udono and the wando ponds, to elucidate the faunal characteristics and species diversity. Ground beetles were captured for a week at 4 sites, Sites 1-4, including a total of 12 sub-sites twice a month from April to December, 2008.

A total of 5,622 individuals of ground beetles belonging to 53 species were captured in this study. Dominant species in the whole sites were Pheropsophus jessoensis, Pterostichus prolongatus, Pt. fortis, Dolichus halensis and Chlaenius pallipes, the former three species of which are known as hygrophilous species. At most sub-sites the dominant species were common to those in the whole sites. However, at 3 sub-sites of Site 1 (Udono), dominant species were different from those in other sub-sites, and they formed a cluster in a dendrogram drawn by the cluster analysis with a similarity index α. The results suggest that an abundance of hygrophilous species has decreased with the aridification of the riverbed at Site 1.