Abstract.1. The adaptive significance of the timing of growth and reproduction by honeybee, Apis mellifera L., colonies in cold climates was studied by describing the seasonal patterns of food storage, brood rearing, and swarming, and then observing the consequences of experimentally perturbing the seasonal cycles of brood rearing and swarming.2. Colonies consume large amounts of food over winter (20+ kg of honey), but have only a brief period (about 14 weeks) for food collection each year.3. The honeybee's striking habits of starting brood rearing in midwinter and swarming in late spring evidently help colonies achieve maximum use of the short summer season. Colonies whose onset of‐brood rearing was experimentally postponed until early spring showed greatly retarded colony growth and swarming. Other experiments demonstrated that late swarms starve more often during winter than do early swarms.4. We conclude that the timings of colony growth and reproduction are essential elements in the honeybee's suite of adaptations for winter surviva