Reunion is a small volcanic island located in the Indian Ocean (21º 06″ S, 55º 36″ E). Though less than 2500 square kilometers in area, its primarily tropical climate can vary markedly from region to region, thanks to dramatic topography that includes the highest mountain in the Indian Ocean, Piton des Neiges, an old eroded volcano that reaches 3069 m. The mean annual rainfall is very high in the eastern part of the island (windward coast) and profoundly lower on the western part (leeward coast). The mean annual temperature varies between 21ºC and 26ºC on the coast, but drops to between 12 and 17ºC at altitude. Urban and cultivated areas cover almost the half of the island, leaving little space for wildlife. Development pressures are most severe in the lowlands (< 1000 m) and in the western part of the island. Only one third of the island contains intact habitats, whereas the remainder has been invaded to varying degrees by introduced species.
Of Reunion's 27 known ant species, more than half are tramp species (Blard et al. 2003). Three invaders are considered the most widespread and damaging: Pheidole megacephala (the big-headed ant), Anoplolepis gracilipes (the yellow crazy ant) and Solenopsis geminata (the tropical fire ant).We are grateful to Jacques Rochat, Thibault Ramage, and Fabrice Blard of the Insectarium de la Reunion for their help in field work in Reunion and for sharing their rich knowledge of the region.