 The probability of a colony usurpation increases steadily as the season progresses, most likely because the probability of a gyne having the time and resources to found a new colony and produce new workers decreases.The increasing risk of usurpation may play a role in the small worker broods, because the queen ceases foraging and seals her nest in mid-May to protect from usurping gynes.Early nest closure has been favored by pressure from usurpation and has developed into an evolutionarily stable strategy.