Over the past thirty years we have learned much about the evolution of mutualists and parasites, especially the evolution of parasite virulence. One unstudied aspect of the evolution of symbioses is how host social structure influences symbiont evolution. To investigate this question I am studying Halictid bees, which include both solitary and social species, and their nematode associates, Aduncospiculum halicti. To determine if there are multiple cryptic species within Aduncospiculum halicti I sequenced a mitochondrial and nuclear gene: Cytochrome Oxidase1 and D2-D3 rDNA. I used both neighbor-joining and maximum likelihood methods to build trees for both genes separately and together. All analyses show that the nematodes cluster by host and not geography, and furthermore form two reciprocally monophyletic clades that correspond with host tribe.