Deserts are interesting places due to the large number of plants and animals that live there. Nocturnal wasps are extremely abundant in deserts, but they are difficult to identify and their life cycles are not well known especially the families of Chyphotidae, Tiphiidae (Brachycistidinae), and Mutillidae (velvet ants). In this dissertation, I determine how to correctly identify a particularly difficult group of species that all have black heads from the family Chyphotidae. This is important because these species make up a large proportion of specimens collected. Also, I expanded our knowledge on the distribution of the species of these three families of wasps by conducting a trap-transect study in Joshua Tree National Park catching 22 species of Brachyscistidinae based on the collection of 13,960 specimens, 11 species of Chyphotes based on the collection of 1,513 specimens and 35 species of velvet ants based on 8,447 specimens. From this study, three new species of velvet ants are described: Odontophotopsis dalyi Sadler and Pitts, sp. nov., O. odontoloxia Sadler and Pitts, sp. nov., and Photomorphus schoenwerthi Sadler and Pitts, sp. nov. Lastly, I used new molecular methods to determine relationships of the species of Brachyscistis, Chyphotes, and Odontophotopsis. These relationships suggest that the species are young, which is contradictory to evidence based on birds and mammals. These relationships also support dates for the inundation of southern California by the Boues Sea Embayment and confirm a hypothesized Baja Inner Peninsular Seaway.

Understanding the history of diversification in the North American deserts has long been a goal of biogeographers and evolutionary biologists. While it seems that a consensus is forming regarding the patterns of diversification in the Nearctic deserts in vertebrate taxa, little work has been done exploring the historical biogeography of widespread invertebrate taxa. Before a robust model of geobiotic change in the North American deserts can be proposed, it needs to be determined if the same historical events affected vertebrate and invertebrate taxa in the same way. I explored the phylogeographic patterns in four groups of widespread nocturnal velvet ants using two rDNA loci, the internal transcribed spacer regions 1 and 2 (ITS1 and ITS2). I used Bayesian phylogenetic analyses and haplotype network analyses to determine if a consistent geographic pattern exists among species and populations within each group. I also used molecular dating techniques to estimate divergence dates for each of the major phylogenetic clades. These analyses indicate that the species-level divergences in some groups occurred in the Neogene, and likely were driven by mountain building during Miocene-Pliocene times (~5 Ma) similar to the divergences in many vertebrate taxa, while species-level divergence in other groups occurred during the Pleistocene (1.8-0.1 Ma) and were likely driven by climatic oscillations and range contractions and expansion. Several recent studies have suggested that Neogene mountain-building events were more important to the development of a diverse desert-adapted biota. My research suggests, however, that both Neogene events and Pleistocene climatic changes were influential in the development of a species-rich nocturnal velvet ant fauna.