New species of Japanese ant will be described in a series of papers. As a first part the following four new species are described: Hypoponera nubatama, Formica hayashi, Acropyga kinomurai and A. yaeyamensis. Hypoponera nubatama is distinguished from the other East Asian congeners by having the following characteristics: antennal scapes reaching the posterior margin of head; eyes consisting of 3 facets and situated near the posterior margin of clypeus; petiolar node thin, with convex dorsal outline; body color black. [Distribution: Japan (Honshu, Kyushu)]. Formica hayashi seemingly resembles F. japonica, but can be distinguished from the latter by the number of erect hairs on 2nd gastral tergite excluding a row of hairs on posterior margin, relatively long antennal scapes and rounded posterolateral corners of head in frontal view. [Distribution: Japan (Hokkaido, Honshu, Shikoku, Kyushu, Yaku-shima; Korea]. Acropyga kinomurai is separated from the other Asian congeners by the 4-toothed mandibles, 11-segmented antennae, small eyes each consisting of 5-6 facets, wide head (CI more than110) and flat dorsum of alitrunk. [Distribution: Japan (Yaeyama Is.)]. Acropyga yaeyamensis is distinctive in having the 4-toothed mandibles, 10-segmented antennae, and small body size (TL less than 2.0 mm). [Distribution: Japan (Yaeyama Is.)].
