Foundresses ofPolistes gallicus(L.) can find themselves deprived of their colonies, particularly after nest predation occurring in the pre-emergence period. This study, conducted mainly in the field, revealed that females who lose their nests resort to two different reproductive strategies: usurpation of an intraspecific colony or foundation of a new nest. The first strategy is only employed in the preemergence period, when the absence of workers on alien nests reduces the risk involved; the second is adopted throughout the season, when a foundress can embark on the project with the help of her workers.