Messor is a diverse genus of Myrmicinae with 168 extant species and subspecies. In the Mediterranean, some of its taxa historically were classified as members of the Messorinstabilis group (sensu Santschi), of which 19 are known from the eastern Mediterranean. Here, the Messorsemirufus complex of the Balkan Peninsula that assembles a distinct subsection of members of the instabilis group is defined and treated. In total, five species are recorded, including three that are new. Messoratanassovii Atanassov, 1982 is redescribed and confirmed for Bulgaria (Thracian Plain, Struma, and Mesta Valley, Pirin Mt., and Eastern Rhodopi) and Greece (Epirus, Ionian Islands, Central and Eastern Macedonia, and Thraki). Three species are described as new to science: Messordanaes Salata, Georgiadis & Borowiec, sp. nov. (Cyclades: Serifos), Messorkardamenae Salata & Borowiec, sp. nov. (Dodecanese: Kos, Nisyros, Rhodes, and Tilos), and Messorveneris Salata, Georgiadis & Borowiec, sp. nov. (Cyclades: Milos). The fifth member of the complex, Messorcreticus Borowiec & Salata, 2019, maintains its status of Cretan endemic.
Keywords: Balkans; Bulgaria; Myrmicinae; eastern Mediterranean; identification key; new species; redescription.
Sebastian Salata, Albena Lapeva-Gjonova, Christos Georgiadis, Lech Borowiec.