Harvester ants (Latreille) (Formicidae: Hymenoptera) have traditionally been labeled as pests within their native ranges from perceived effects on crop production and rangeland productivity.Yet, modern research casts doubt on many of these perceived detrimental effects and instead suggests that harvester ants act as keystone species that largely benefit both ecosystems and human activities.Through nest engineering and trophic interactions (such as seed harvesting and predation), harvester ants have considerable direct and indirect effects on community structure and ecosystem functioning. Here we summarize the ecological roles of harvester ants and review their services and disservices to ecosystems and human activities. In doing so, we help clarify perceived keystone and pest roles of harvester ants and their implications for rangeland management. We find the numerous keystone roles of harvester ants to be well-supported compared to perceived pest roles.We also highlight areas where further research into their roles in natural and managed systems is needed.