Key to the species with outdoor occurrence in the Palaearctic In order to comprise all 34 species with outdoor occurrence in the Palaearctic, the key and the supplementary information SI1 and SI2 additionally included nine species of species groups with other zoogeographic origin. These species either extend their range into the southern Palaearctic or are globally dispersing tramp species potentially occurring in each locality with sufficiently warm climate. The complete taxonomic names of these added species are Cardiocondyla minutior Forel 1899, C. tjibodana Karavajev 1935 and C. goa Seifert 2003 (all three belonging to the C. minutior species group), C. emeryi Forel 1881 (belonging to the C. emeryi species group), C. fajumensis Forel 1913 and C. unicalis Seifert 2003 (both belonging to the C. shuckardi species group), C. wroughtonii (Forel 1890) and C. obscurior Wheeler 1929 (both belonging to the C. wroughtonii species group) and C. mauritanica Forel 1890 (belonging to the C. nuda species group). The key presented below almost thoroughly used dichotomous decision schedules for cases requiring combinations of multiple characters and in the same time it aspired to achieve a low error rate inevitably resulting in tedious procedures. Lamenting does not help here and those who think that simple answers can be given for difficult problems bark up the wrong tree. The finally best approach is here using a software providing linear discriminant functions (LDA), measuring the full set of morphometric characters and running the investigated samples as wild-cards within the data space of the hypothesis-providing supplementary file SI2. It is convenient to run the analysis with primary (raw) measurements instead with ratios. A good check of the result is then comparing with the images that are given for any species in four aspects and to consider geographic distribution. The low error rates reported in the key cannot be achieved for such tiny ants without high-resolution optical systems, a good measuring stage and a careful realization of character definitions. 1a Anterior postpetiolar sternite laterally more prominent than in median part—as result an imagined cross section shows a deeply concave ventral margin of the sternite. The lateral protrusions appear in frontolateral view as dents (Fig. 113). C. wroughtonii group............................................................................................... 2 1b Anterior postpetiolar sternite in median part more prominent or at equal level as the lateral surface—as result an imagined cross section shows a convex or straight ventral margin of the sternite................................................ 3 2a With all measurements in mm, discriminant 34.21* CW-59.33 *PoOc-177.83* EYE +72.15* SL-113.56 * FRS-106.46 *SP+140.69*PpW-14.15 0 [0% error in 65 nest sample means of two workers]. 1 st gaster segment in a majority of samples with strongly developed blackish pigmentation. Worldwide tramp species. Outdoor occurrence confirmed for southern Spain and the Middle East. Figs.109–113 ............................................................................. obscurior 3a True foveolae on vertex dorsal of the eyes completely absent. Instead the bases of pubescence hairs are placed in the center of flat tubercles or flat pits of only 4–10 µm diameter, giving a finely punctate surface appearance at lower magnifications (Figs. 89, 97). Postocular distance large, PoOc/CL 0.416 –0.467. Frons usually very wide, FRS/CS> 0.288 (except C. tibetana, here 0.280 ± 0.006). Propodeal spines reduced to blunt dents. Metanotal depression deep. C. stambuloffii group.............. 4 3b Bases of pubescence hairs on vertex dorsal of the eyes placed in the center of foveolae or cuticular meshes of> 10 µm diameter (Figs. 9, 25, 117)—if foveolae reduced (verdensis n. sp.), than PoOc/CL 0.235. Frons narrower, FRS/CS 0.295, PeH/CS>0.343, PpH/CS 2.3. South Kazakhstan. Figs. 98–100 ........................... gibbosa 5b Posterior part of vertex not completely smooth, at least with weak rugulae and small tubercles around the bases of pubescence hairs. Discriminant 0.4 [0% error in 59 individuals]..................................................................................... 7 7a With all measurements in mm, discriminant 120.6*PoOc-29.53*SL+109.54*PeW-109.42*PeH-157.97*PLG-7.70 0.7 [0% error in 22 individuals]. Figs. 90–93 ......................................... koshewnikovi 8a Propodeal spines reduced to obtusely angled corners (Fig. 115). Postpetiole rather narrow, PpW/CS 0 [error 0% in 17 individuals].......................................................................... 9 8b Propodeal spines not reduced to obtusely angled corners. If spines occasionally reduced to blunt corners, then EYE/CS> 0.221 and PpW/CS>0.450. Discriminant 1.16 (Fig. 114). Dorsum of promesonotum and lateral pronotum with more developed microsculpture (Figs. 115, 116). Head sculpture stronger, foveolae with regular margin (Fig. 117). Egypt and Saudi Arabia .......................................................................................................... fajumensis 9b Head very short CL/CW 0 [error 0% in 863 specimens].......... 11 11a Small, CW 420 mm. Minute specimens of C. mauritanica may match the character combination of 11a but differ by shorter spines and a thinner petiolar peduncle (compare Figs. 127 and 130)............................................ 12 12a Outlines of postpetiole in dorsal view approximately hexagonal (Fig. 131). Metanotal depression shallow (MGr/CS 2.14±0.52). Propodeal spines developed as short dents (Fig. 130). Gastral pubescence dense (sqPDG 3.72 ± 0.28). Postocular distance large (PoOc/CL 0.447 ± 0.008, Fig. 129). Microsculpture on vertex strongly reticulate (Fig. 132). With MGr, PoOc and SP in mm and sqPDG in µm, discriminant 136.0*MGr-25.0*PoOc*73.99*SP+1.81*sqPDG-7.2322 0 [error 0.3% in 619 specimens]............................................................ 13 13a Postocular distance extremely small (PoOc/CL 0 [error 0% in 612 specimens]...................................................................................... 14 14a Head surface between inner eye margin and paramedian vertex strongly microrugulose (Fig. 69). Dorsal promesonotum longitudinally microrugulose (Fig. 68).All surfaces of head, mesosoma and petiole matt due to more developed microsculpture. Dorsal profile of mesonotum straight, contrasting the clearly convex dorsal profile of propodeum, metanotal depression feebly suggested (Fig. 67). With all measurements in mm, discriminant 95.88*EYE-164.99*MGr-12.035> 0. Yemen. Figs. 66–69 ............................................................................................... rugulosa 14b Body surfaces less microrugulose, often shiny. Dorsal profile of mesosoma different. Discriminant 0 [error 0% in 177 individuals]. C. elegans group................................................................................................... 18 17b Discriminant 0 [error 0% in 81 two-specimen nest samples]. Figs. 6–9 ................................................... elegans 18b Occurring farther east. If found in NE Italy or Slovenia, discriminant 2 [error 0% in 13 specimens]. S Georgia, NE Turkey, Iran, Afghanistan. Figs. 18–21 ...... brachyceps 19b Foveolar diameter smaller, postpetiolar height larger, spines shorter, pubescence distance smaller. Discriminant 2 [error 0% in 6 specimens]. Asia Minor. Figs. 14–17 ............... dalmaticoides n. sp. 20b Bases of propodeal spines more distant, petiole wider and lower, surface of propodeum less glabrous, propodeal spines less acute, petiole lower with a less steep anterior profile of the node. Discriminant 0 [error 0.4% in 241 individuals]. Species of the C. ulianini group................................. 25 22a Frontal carinae notably diverging frontad, FL/FR>1.109. Postocular distance large, PoOc/CL>0.408. Metanotal depression very shallow, MGr 2.5 %................................................................................. 23 23a Petiole massive, ratio PeW /PpW> 0.57. With all measurements in mm, discriminant 152.578*PeW-69.53*PpW+2.092*SL+3 0.63*PoOc-10.57> 2.5 [error 0% in 4 individuals]. Only known from two sites in Asia Minor. Figs. 58–61 ....... semirubra 23b Petiole less massive, ratio PeW/PpW in 97% of individuals 0 [error 0% in 95 specimens]. Portugal, Morocco, Algeria, Tunisia, Egypt, Cyprus, Turkey, Middle East, Iran eastwards to 56°E. Color polymorphic. Figs. 78–81 ....................................................... nigra 25a Frons very narrow, FRS/CS 0.225; propodeal spines acute but very short, SP/CS 0.071; postocular distance small, PoOc/CL 0.403; postpetiole wide PpW/CS 0.552. With all measurements in mm, discriminant 160.18*FRS+41.17*PoOc-45.99*PpW- 15.23 0 [error 0% in 240 specimens]......................................................................................... 26 26a Combination of large propodeal spine base distance, small eye, large postocular distance, broad and high postpetiole. With all measurements in mm, discriminant 44.74*PoOc-167.14*EYE+161.96*SPBA-56.07*PpW+31.77*PpH+0.543>0 [error 0% in 179 specimens]...................................................................................... 27 26b Propodeal spine base distance smaller, eye larger, postocular distance smaller, postpetiole narrower and lower. Discriminant 0.5 [error 0% in 84 specimens]. S Balkans and Asia Minor. Figs. 42–45 ............................................................... bulgarica 27b Discriminant 0 [error 7.7% in 26 specimens]. Georgia, Iran. Figs 50–53 ........... persiana 29a Vertex with rather large, well-demarcated, bicoronate and densely-packed foveolae and in anteromedian part with well-developed longitudinal sculpture(Figs. 38, 41). Pubescence on gaster tergites more dense. With dFOV, sqPDG in µm and SPBA in mm, discriminant 2.559*sqPDG-0.472*dFov+15.117*SPBA-4.857 0 [error 0% in 51 specimens]............................. 30 30a Postpetiole and frons wider, pubescence hairs on gaster tergites shorter. With all measurements in mm, discriminant 93.21* FRS +27.62*PpW-406.34* PLG-6.246> 0 [error 0% in 44 specimens]. Continuously distributed from the S Ukraine (32°E) eastwards to N Xinjang (88°E). Figs. 22–25 ..................................................... ulianini 30b Postpetiole and frons narrower, pubescence hairs on gaster tergites longer. Discriminant 93.21* FRS +27.62*PpW-406.34* PLG-6.246 0.423, PpH/CS> 0.260). Foveolae on vertex mediad of eye with diffuse margins (Fig. 29). Anterior face of petiole node moderately sloping down (Fig. 27). SE Kazakhstan. Figs. 26–29 .............................................................................................. littoralis 31b Postocular distance and postpetiole height smaller (PoOc/CL <0.423, PpH/CS <0.260). Foveolae on vertex mediad of eye more strongly demarcated and bicoronate (Fig. 33). Anterior face of petiole node steeper (Fig. 31). Iranian Caspi region. Figs. 30–33 .................................................................................. caspiense n. sp.

Published as part of Seifert, Bernhard, 2023, A revision of the Palaearctic species of the ant genus Cardiocondyla Emery 1869 (Hymenoptera: Formicidae), pp. 1-64 in Zootaxa 5274 (1) on pages 8-11, DOI: 10.11646/zootaxa.5274.1.1, http://zenodo.org/record/7888156