Technical Abstract: With hundreds of species established in new localities around the world, ants are an important, widely distributed, and growing group of exotic animals. The success of many established exotic ants is hypothesized to be related to competitive advantages associated with smaller workers and larger colonies relative to co-occurring native species. To evaluate this hypothesis, ant assemblages were thoroughly sampled across the range of upland ecosystems in north-central Florida, a region with one of the most diverse exotic ant faunae in the world. Patterns of species richness, abundance, worker body size, and colony size were compared among species and ecosystems. We found that exotic ants were neither abundant nor diverse in any of the undisturbed upland ecosystems. In disturbed field sites, exotic ants accounted for about 40% of total ant abundance and 25% of species richness. A total of 94 species, including 13 exotic species and 9 endemic species, were captured. The average body size of exotic ants was not obviously different from related native species. The average colony size of exotic ants was smaller than native species, with the exception of Solenopsis invicta which had the largest colony size of all species. Introduced ants (including S. invicta) were neither speciose nor abundant in any of the native woodland ecosystems. Florida's intact, native upland ecosystems appear to be resistant to invasion of exotic ant species despite the fact that surrounding disturbed habitats host a large diversity and abundance of introduced species. The prediction that exotic species have smaller workers than related native species was not supported.