The ant genus Pheidole is a spectacular radiation at the species level. 1500 ha of lowland rainforest in Costa Rica contain 78 species, comprising 17% of the total ant fauna. Adding montane specialists on the adjacent slope raises the number of species to 111, and larger-scale species turnover yields 152, 624, and 1165 known species for Costa Rica, the New World, and the World respectively. Pheidole species have an ecological breadth nearly as wide as all ants combined, occupying all strata of forested habitats, living in moisture regimes ranging from rainforests to deserts, and exhibiting an array of feeding behaviors including predation, omnivory, herbivory (as partners in ant-plant mutualisms), and granivory. The high species richness and broad ecological diversity is not reflected in morphology: Pheidole morphological diversity is highly constrained. Current research aims to (1) improve the taxonomic infrastructure for the genus by continuing species description and providing matrix-based identification tools; (2) reveal its phylogenetic and biogeographic history using molecular techniques; (3) understand the evolutionary and macroecological processes that generate this kind of radiation; and (4) assess the impact of habitat loss and climate change on this hyperdiverse invertebrate taxon.