Abstract: A numeric morphology-based alpha-taxonomy (NUMOBAT) analysis confirmed cryptic heterospecificity of Cardiocondyla atalanta Forel, 1915 from Cardiocondyla nuda (Mayr, 1866). A discriminant analysis (DA) considering 14morphological characters confirmed all a-priori-determinations of 48 C. atalanta and 84 C. nuda worker specimensand allocated the holotypes of C. atalanta and C. nuda to the corresponding cluster with p = 0.999 and p = 1.000, respectively. The Leave-One-Out Cross-Validation (LOOCV) test indicated an error rate of 0 %. Cardiocondyla atalantadiffers from C. nuda in the worker caste by having a shorter and less dense pubescence on first gaster tergite and a shorterscape. Simulations indicate that a single character, absolute pubescence length on first gaster tergite, should enable asafe species discrimination if nest samples containing three workers are available. The distribution of both species differs considerably. Cardiocondyla nuda is distributed in Polynesia east to 170° W, in New Guinea and along the coast ofnorthern and eastern Australia. It avoids continental parts of Australia and is apparently best adapted to climate zoneswith annual rainfalls above 1000 mm. Cardiocondyla atalanta ranges all over the Australian continent, including its innermost parts, and is only exceptionally found on offshore islands of Australia. It is better adapted to a xerothermous climatewith annual rainfall below 1000 mm. Both species are sympatric in the coastal areas of northern and eastern Australia.Syntopic occurrence was only once observed but is most certainly underrecorded because of low sample numbers.