The previous concept of the cosmopolitan pest ant Tapinoma melanocephalum (Fabricius, 1793) includes two species (Hymenoptera: Formicidae: Tapinoma)

Abstract

Tapinoma melanocephalum (Fabricius, 1793), known under the vernacular name Ghost Ant and being a widely distributed cosmopolitan tramp species with significant pest status, has been considered long-since to represent a single species. Yet, investigation of 83 worker samples from the whole globe provided evidence that the Ghost Ant consists of two species: 8.4 % of the samples belonged to the new species T. pithecorum sp. nov. whereas 91.6 % were classified as T. melanocephalum. Absence of mixed samples indicates that T. melanocephalum and T. pithecorum sp. nov. do not represent morphs of the same species. T. pithecorum sp. nov. is known from a greenhouse finding in Germany and outdoor populations from the south of the Arabian Peninsula, Pakistan, India, Malaysia and the Fiji and Christmas Islands. The phenotypical separation of the new species from other minute Tapinoma species of Orientalic, Indo-Australian and Australasian origin is very clear, allowing identification even by evaluation of z-stack photos. A detailed argumentation is presented that Tapinoma pellucida (Smith, 1857), T. coronatum (Forel, 1908), T. malesianum (Forel, 1913), T. australis (Santschi, 1928), T. australe (Santschi, 1928), T. luffae (Kurian, 1955), T. wallacei (Guerrero, 2018) and T. jerdoni nom. nov. should be considered as synonyms of T. melanocephalum. Synomymies of T. melanocephalum and T. pithecorum sp. nov. with T. indicum (Forel, 1895) and Tapinoma minutum (Mayr, 1862) are clearly excluded by morphometric data. Diagrams of principal component analyses, photos, a key as well as a morphometric table to separate these four species are presented. In a concluding section, is argued that the true number of species related to these four species is much larger than presently known and a warning is given regarding careless use of pigmentation characters in ant identification.