The primitively eusocial bee, Bombus (Fraternobombus) griseocollis, possesses a complex temporal division of labor based on shifting patterns of principal tasks rather than on discrete age castes. Workers within a given age range perform ensembles of tasks which change quantitatively as the workers age. Functional classes of behavior, such as nursing or guarding, are not limited to a given age class of workers; all tasks are performed by workers of all ages. Colony ontogeny also influences worker behavioral ontogeny; significant differences in task performance exist among workers born in different phases of colony development. As the colony aged, young bees foraged with increasing probability. In the absence of foraging mortality, foragers shifted to nursing tasks, and were replaced by younger bees.