Native and exotic ants (Hymenoptera: Formicidae) nesting in red mangroves (Malpighiales: Rhizophora mangle) of eastern Florida

Red mangroves (Rhizophora mangle) grow in and adjacent to shallow brackish water in subtropical and tropical estuaries around the world, and provide a unique arboreal habitat, often completely isolated by water from any terrestrial habitat. I collected ants nesting inside the hollow dead twigs, small branches, air roots, and prop roots of red mangroves at 98 sites in 9 counties along the east coast of Florida, from Volusia County in the north to the Upper Keys of Monroe County in the south. I found a total of 22 ant species nesting in red mangroves, including ten native species, eight exotic species (four Old World, four New World), and four New World species whose status in Florida is uncertain. The most common species by far were two native species (Tapinoma litorale and Xenomyrmex floridanus). The next three most common species, however, were exotics (Monomorium floricola, Pseudomyrmex gracilis, and Technomyrmex difficilis). I also collected the first Florida specimens of Crematogaster steinheili, a species that is very common in red mangroves of the West Indies, but may be exotic to Florida. Several native and exotic species show strikingly similar ecologies. For example, native X. floridanus and exotic M. floricola are both tiny, thin, short-legged, slowmoving myrmicine ants that cling tenaciously to surfaces. Earlier studies indicate that native ant species compete for resources in red mangroves. It seems likely that exotic ant species in the red mangroves also compete with and may threaten the native ant species.