Since the introduction of the hemlock woolly adelgid (HWA, Adelges tsugae) in the 1950s, eastern and Carolina hemlock (Tsuga canadensis, T. caroliniana) stands have greatly declined throughout eastern North America. Because of the importance of hemlocks, much research has been done to manage this pest. Currently, the use of biocontrol predators is a priority for research as it would naturally control HWA populations without the use of insecticides; insecticides, while effective, are costly and cannot be applied across large landscapes. Two potential biocontrols are silver fly species native to the Northwestern US, Leucotaraxis argenticollis and Leucotaraxis piniperda, as they are natural predators of HWA found in that region. Due to many similarities between the two species and difficulty of identification, especially for immatures, they have historically been lumped together, but currently, there is research looking into the differences between the two species. This paper looks specifically at the differences in longevity, length of their pre-oviposition period, oviposition, and impact that availability of live HWA has on their oviposition. It was found that L. piniperda lived longer than L. argenticollis (48.4 days compared to 25.7 days), that the length of pre-oviposition period for L. piniperda was greater than that of L. argenticollis (23 days compared to 14 days), and that there was a positive correlation between the number of live HWA on a twig and the number of eggs laid for L. argenticollis but not for L. piniperda. Understanding these differences helps us further understand the biology of these two species which is important in the context of using them as biocontrols for HWA.