We report 12 new observations of parasitically-founded Vespula flavopilosa colonies. Of these, 4 nests were identified directly by having been found in the pre-emergence stage, whereby only the resident queen was seen foraging before the presence of the first workers. Seven nests were found in the early phases of worker production, wherein the queen and first workers were foraging simultaneously, or nests were observed containing workers of both the host V. maculifrons and parasite V. flavopilosa freely foraging together. A twelfth nest, collected later in the season, appeared to have been the result of a usurpation of a V. germanica nest, based on gray paper found in the central cores of the first three combs of the nest. This represents the first report of V. flavopilosa utilizing the introduced V. germanica as a host species. These observations cover a wide part of the species' range, and imply that V. flavopilosa is a frequent temporary social parasite. Furthermore, this behavior appears to be obligatory since an incipient nest founded unequivocally by a V. flavopilosa queen has not been recorded.