Further additions to the knowledge of Strumigenys (Formicidae: Myrmicinae) within South East Asia, with the descriptions of 20 new species

The species of the ant genus Strumigenys Smith, 1860 from Southeast Asia are reviewed based on recent sampling efforts as well as unreported historical material from southern mainland China, Japan, Taiwan, Thailand and Vietnam. We report 42 new species records for these regions. A total of 20 species new to science are described: S. anhdaoae sp. nov., S. claviseta sp. nov., S. crinigera sp. nov., S. decumbens sp. nov., S. delicata sp. nov., S. densissima sp. nov., S. doydeei sp. nov., S. fellowesi sp. nov., S. intermedia sp. nov., S. jaitrongi sp. nov., S. liuweii sp. nov., S. longidens sp. nov., S. mediocris sp. nov., S. rongi sp. nov., S. scutica sp. nov., S. strummeri sp. nov., S. xenopilus sp. nov., S. yamanei sp. nov., S. zanderi sp. nov. and S. zhenghuii sp. nov. The descriptions of the existing species S. elegantula (Terayama & Kubota, 1989) and S. nathistorisoc Tang et al., 2019 are revised. Strumigenys formosensis Forel, 1912 syn. nov. is synonymized with S. feae Emery 1895 in the light of recently collected specimens. Three species complexes are created within the S. leptothrix-group: elegantula-complex, leptothrix-complex and zanderi-complex, based on differences in dentition. A new species group, S. nathistorisoc-group, is introduced. The key to Strumigenys of East Asia (as Pyramica) by Bolton is partially revised to accommodate species from these species groups that were described since the publication of the key. Finally, the implication of our results to the region and the current limitation of species groups and complexes of the genus is discussed.