Xenomyrmex floridanus Emery (Hymenoptera: Formicidae) is a small arboreal ant known only from peninsular Florida and the West Indies. Xenomyrmex floridanus colonies nest in plant cavities, particularly in hollow twigs and dead branches. I compiled and mapped >100 site records for X. floridanus, documenting the earliest known records for the 4 geographic areas where it occurs: peninsular Florida, the Bahamas, Cuba, and Jamaica. Records of X. floridanus range from Gainesville, Florida (29.7°N) in the north to Pedro Cross, Jamaica (18.9°N) in the south. Xenomyrmex floridanus shows striking evolutionary convergences in morphology and behavior with Monomorium floricola (Jerdon) (Hymenoptera: Formicidae), an Old World tramp ant species that has spread worldwide through human commerce. Both species are tiny, thin, and short-legged, a morphology that allows them to nest in very narrow plant cavities. In addition, both are slow moving and have an exceptional ability to cling to surfaces, a capacity that probably allows them to avoid being blown out of trees, even in high winds. Monomorium floricola has invaded Florida and the West Indies, where it may negatively impact X. floridanus populations. In red mangrove (Rhizophora mangle L.; Rhizophoraceae) in southeastern Florida, I found that X. floridanus is the most common native ant and M. floricola is the most common exotic ant.