The subfamily Oraseminae (Hymenoptera: Chalcidoidea: Eucharitidae) is a circumtropical group of parasitoid wasps that specialize on ants in the subfamily Myrmicinae (Hymenoptera: Formicidae). Multiple phylogenetic inference methods, including parsimony, maximum likelihood, Bayesian, and coalescence, with the largest to date sampling of taxa for this subfamily allow us to elucidate their dated biogeography, ancestral host ant genus, diversification rates, and provide valuable data for revising the constituent genera and species. Using molecular datasets comprised of Illumina sequences from Anchored Hybrid Enrichment probe capture, Sanger sequences from paired primers, and a combination of the previous two datasets, we show that Oraseminae has likely dispersed from the Old World into the New World across a tropical Beringian Land Bridge approximately 24–33 Ma. This dispersal, which seemed to have occurred around the same time but in the opposite direction of their ancestral host ants in the genus Pheidole, led to an increased diversification rate in the exclusively New World genus, Orasema. Including the species described herein, Orasema comprises 94 described species organized into 16 species groups with several unplaced taxa. There are 22 new species described and 7 redescriptions with comprehensive distribution maps, plant and ant host association data, and digitally imaged photo plates, which represents the largest revision of this genus to date. Within the superfamily Chalcidoidea, eucharitid wasps, along with their sister family, Perilampidae, have a unique morphology for their first-instar larvae called planidia, which are hypermetamorphic, highly mobile, and strongly sclerotized. Relationships to this planidial clade have historically been difficult to establish. A morphological phylogenetic analysis of the planidial larvae that includes the newly discovered, less-derived larva in the species Eutrichosoma mirabile Ashmead (Pteromalidae) has provided evidence of a close relationship to the Eucharitidae and Perilampidae, allowing us to make more informed predictions on the origin and natural history of planidial larvae in Chalcidoidea.