The biology of the Hemileuca maia group of “buck moths” in the Great Lakes region is summarized, especially with respect to the northern “maia complex” where adult phenotype is not well-correlated with either pheromone response or perceived host plant associations. Published field trials of pheromone response are updated with respect to host plant associations. We found a reciprocal lack of response to pheromone between willow-feeding “complex” moths in lowland, glaciated habitats to the north and oak-feeding populations in non-glaciated habitats to the south. We discuss how post-glacial host plant distributions — expansion from previous refugia and forestation of the Great Lakes terrain — may have played a key role in structuring current Great Lakes Hemileuca populations. In addition, the subsequent rapid and extreme drying during the mid-Holocene (8,000–3,200 years BP) led to the expansive tall grass prairie, producing a finger-like eastern extension known as the Prairie Peninsula, which probably provided an additional ecological barrier separating these oak and willow-feeding populations. Rapid expansion of willow-feeding populations from Pleistocene refugia after 18,000 years BP offers a more likely explanation, compared to gene flow, for the general lack of genetic divergence previously found in the buck moths of the Great Lakes region.