Temnothorax (Formicidae: Myrmicinae) is a diverse genus of ants found in a broad spectrum of ecosystems across the northern hemisphere. These diminutive ants have long served as models for social insect behavior, leading to discoveries about social learning and inspiring hypotheses about the process of speciation and the evolution of social parasitism. This genus is highly morphologically and behaviorally diverse, and this has caused a great deal of taxonomic confusion in recent years. Past efforts to estimate the phylogeny of this genus have been limited in taxonomic scope, leaving the broader evolutionary patterns in Temnothorax unclear. To establish the monophyly of Temnothorax, resolve the evolutionary relationships, reconstruct the historical biogeography and investigate trends in the evolution of key traits, I generated, assembled, and analyzed two molecular datasets: a traditional multi-locus Sanger sequencing dataset, and an ultra-conserved element (UCE) dataset. Using maximum likelihood, Bayesian, and summary-coalescent based approaches, I analyzed 22 data subsets consisting of 103 ingroup taxa and a maximum of 1.8 million base pairs in 2485 loci. The results of this study suggest an origin of Temnothorax at the Eocene-Oligocene transition, concerted transitions to arboreal nesting habits in several clades during the Oligocene, coinciding with ancient global cooling, and several convergent origins of social parasitism in the Miocene and Pliocene. As with other Holarctic taxa, Temnothorax has a history of migration across Beringia during the Miocene. Temnothorax is corroborated as a natural group, and the notion that many of the historical subgeneric and species group concepts are artificial is reinforced. The strict form of Emery’s Rule, in which a socially parasitic species is sister to its host species, is not well supported in Temnothorax.

Four new Afrotropical species of the ant genus Temnothorax are described and illustrated, all from Kenya. Based upon high resemblance to taxa known from the North African and Iberian territories of the Mediterranean region, these new tropical elements are placed into known Palaearctic species complexes. Specifically, T. brevidentis sp. n., T. mpala sp. n. and T. rufus sp. n. are placed in the laurae species group, and T. solidinodus sp. n. is placed in the angustulus species group. Two already known Temnothorax species from the region, T. cenatus (Bolton, 1982) and T. megalops (Hamann & Klemm, 1967), are also placed into the laurae species group based on the high number of shared morphological characters. Diagnoses for the African representatives of laurae and angustulus species groups of the Afrotropical biogeographical region are provided. A key to workers of the six Temnothorax species known to occur in the Afrotropical biogeographical region is provided, as well as diagnoses of morphologically similar myrmicine genera.

Temnothorax (Myrmicinae, Crematogastrini) is one of the most diverse Holarctic ant genera, and new taxonomic advancements are still frequent worldwide. The Mediterranean region, a global biodiversity hotspot characterized by a complex geographic history, is home to a substantial portion of its described diversity. Sicily is the region’s largest island and, as ongoing investigations are revealing, it is inhabited by a long-overlooked but highly diverse ant fauna that combines multiple biogeographic influences. We combined qualitative and quantitative morphology of multiple castes with phylogenomic analysis based on ultra-conserved elements (UCEs) to describe four species of Temnothorax endemic to Sicily and the neighboring Maltese Islands (Sicilian Channel). Three of these species, T. marae Alicata, Schifani & Prebus sp. nov., T. poldii Alicata, Schifani & Prebus sp. nov. and T. vivianoi Schifani, Alicata & Prebus sp. nov., are new to science, while a redescription clarifies the identity of T. lagrecai (Baroni Urbani, 1964). These descriptions highlight the current difficulties of delimiting monophyletic Temnothorax species groups based on morphological characters. The intra-insular endemicity patterns we revealed highlight the importance of Mediterranean paleogeography to contemporary ant diversity and distribution in the region.

The following ten new species of the ant genus Temnothorax are described and illustrated: T. anaphalantus (California, Baja California), T. arboreus (California), T. caguatan (Oregon, California, Baja California), T.morongo (California, Baja California), T. myrmiciformis (California, Baja California), T. nuwuvi (Nevada), T. paiute (California, Nevada), T. pseudandrei (Arizona, California), T. quasimodo (California) and T. wardi (California). A key to workers of the twenty-two Temnothorax species known or expected to occur in California is provided.