Quercus velutina (Black Oak) is a dominant deciduous tree in Cape Cod, Martha's Vineyard, and Nantucket, MA. In recent years, Black Oak trees in these regions have experienced severe canopy loss due to the infestation of a stem-gall wasp, Zapatella davisae. In addition to infestations first documented in the Cape Cod region in 2012, Zapatella davisae has been present in Long Island, NY, since the 1990s. We investigated the life cycle of Z. davisae, specifically emergence patterns and timing of development. We evaluated differences in the severity of the infestations in Long Island and Cape Cod. We also identified towns in Cape Cod that contained Z. davisae infestations to better estimate the geographic extent of the infestation in the region. We found that Zapatella davisae completes 1 generation per year and emerges throughout the month of May. The severity of the infestation was the greatest in Cape Cod, an indication that something is controlling the population in Long Island. We concluded that Z. davisae is widespread and present in all towns in Cape Cod, Nantucket, and Martha's Vineyard. Our research will lay the foundation for future biological control efforts and will help arborists and landowners make management decisions regarding Z. davisae in the Cape Cod region and Long Island.