In chapter 2, the range of Axymyia furcata McAtee (Diptera: Axymyiidae), a xylophilic semi-aquatic lower Dipteran once considered to be rare, is expanded to include twenty U.S. states and two Canadian provinces. Collecting and rearing methods are described, including the use of the niche modeling software, DIVA GIS, to locate regions with potentially suitable habitat for A. furcata. The life history of A. furcata is discussed, with emphasis on habitat, phenology, and the types and condition of the wood in which the larvae of A. furcata reside. In chapter 3, the morphology of Axymyia furcata McAtee (Diptera: Axymyiidae), a semi-aquatic nematocerous fly, is documented at all life stages: egg, larva, pupa, and adult. The morphological description is supplemented with numerous SEM images, photos, and drawings. Chapter 4 focuses on reconstructing how the last glacial maximum and post-glacial expansion from southern refugia has affected the genetic distribution of North American species. We attempt to uncover these patterns for Axymyia furcata, a semi-aquatic member of the nematocerous Diptera from the eastern Nearctic. We sampled 114 individuals from across their known range including populations in 18 states. We sequenced a 710-bp fragment of the mitochondrial cytochrome c oxidase subunit 1 gene (Cox I). From our analyses it appears the A. furcata expanded northward from a southern Appalachian refugium, and may have also survived the last glacial maximum in to northern refugia located in the Driftless area and southeastern Ohio.