The Hawaiian Islands are the most isolated land mass in the world, and lacked ants before the arrival of humans. Our research focuses on invasion biology and behavioral ecology of five introduced ant species in Hawaii: Leptogenys falcigera (Roger), Camponotus variegatus (Smith), Anoplolepis gracilipes (Smith), Ochetellus glaber (Mayr), and Pheidole megacephala (Fabricius). Laboratory bioassays were performed to assess agonistic interactions. Both individual and group assays were conducted, pairing either individual ant workers or groups of ten workers from each species, respectively. Individual assays were scored using a rating system ranging from aggressive to avoidance behavior. Group assays were evaluated on the basis of ant mortality, in that aggression led to mortality. The species with the highest and lowest levels of agonistic behavior were similar in the individual and group experiments, Pheidole megacephala ranked first in agonistic behavior with the highest level of aggression in the individual assays and high mortality in group assays. Anoplolepis gracilipes was ranked second in aggressive behavior in individual assays and second in group assays. Leptogenys falcigera was the most non-responsive in individual assays, and had 100% survival in the group trials. Field observations that P. megacephala and A. gracilipes are dominant species and L. falcigera is a subdominant species on Oahu, are in agreement with these experimental results.