In "X. virginica," mating occurs only once a year, in the spring. Eggs are laid in July, starting farthest from the exit hole, and by about August and mid-September, larval development has completed and all the pupae have become adults. Researchers suggest that there is a mechanism that synchronizes the emergence time of young that are laid at different times by causing the younger eggs to develop faster. This mechanism prevents bees that would emerge sooner from removing their siblings and decreasing their potential competition.