Monomorium sahlbergi Emery, 1898 (Formicidae, Hymenoptera): a cryptic globally introduced species

The discovery in the Netherlands in a shipping container of the ant Monomorium sahlbergi Emery, 1898, a species similar to the invasive pharaoh ant M. pharaonis (Linnaeus, 1758), led to a quest to better define the distribution of this species, which was initially obscure due to uncertain specimen identifications. Here it is shown that M. sahlbergi, like M. pharaonis, is found worldwide, almost certainly as a result of introductions. Including quarantine interceptions, this species is recorded from seven global biogeographic regions, but its established outdoor distribution is currently limited to the tropics and subtropics. Monomorium dichroum Forel, 1902 is here presented as a junior synonym of M. sahlbergi syn. nov. based on morphometric and CO1 analyses.