Where Do Bee Pollinators Go During the Winter?

So, you may be wondering: where do bees go during the winter? Well, it depends on the type of bee. Overall, bees use three types of strategies to survive the winter.

Active adults:  Honey bees (Apis mellifera) are the only species in the mid-Atlantic region that remain active year-round. Honey bees overwinter as adults inside the hive. During the winter months, they actively feed on the honey reserves available in the nest. The transition between regular workers to winter bees occurs in the fall due to changes in temperature and photoperiod. Physiologically and behaviorally, winter honey bees are different from summer bees because they stop rearing brood in the nest and, most importantly, form a thermoregulating cluster (Figure 1). Through the vibration of their flight muscles, honey bees generate heat and maintain the core temperature of the cluster between 77ºF and 95ºF (25ºC and 35ºC). In contrast, the temperature of the exterior of the cluster ranges between 43ºF and 54ºF (6ºC and 12 ºC). Because of the heat generated by the cluster, honey bees are capable of rearing brood when it is still cold (brood rearing can begin as early as January) so that young worker bees are ready to forage as soon as the weather warms up in the spring.

Figure 1. The photo on the right shows how well the honey bees generate heat and maintain the core temperature of the cluster during winter. Photos: Robyn Underwood, Penn State

Hibernating mated females:  Another strategy used by social bees and some solitary bees is overwintering as adults but in a hibernating state. This strategy is used by bumble bees, carpenter bees, and some sweat bees (both social and solitary) (Figure 2). After mating in the fall, females of these bees spend their time consuming as much pollen and nectar as possible before winter to increase their fat reserves. After that, these bees also need to look for overwintering sites, which can be dry leaves, rotting logs, and, in some cases, their natal nests. Once the overwintering places are located, females enter a stage called diapause, where bees reduce their metabolism and use the fat reserves stored in their bodies to survive the cold winter months. For the social species that use this overwintering strategy, mated queens are the individuals that will hibernate in overwintering sites until the right time to emerge the following year. When these mated females emerge in the spring, they begin nest construction and foraging activities to rear the first brood of the new colony. Once the first generation of workers emerges, the queens stay in the nest, primarily laying eggs.

Figure 2. (Left) a solitary sweat bee (Katy Evans, Penn State). (Center) large carpenter bee, (Right) bumble bee (Nash Turley, Penn State).

Diapausing adults or prepupa:  The vast majority of bee species in the mid-Atlantic region are solitary and overwinter inside their natal nest (Figure 3). Unlike the social species, where mated females actively feed on flowers in the fall to use those reserves for overwintering, solitary bees that have annual cycles overwinter in their nests before emerging. For these species, eggs hatch into the larval stage that can feed on the pollen and nectar provisioned by their mother before they turn into diapausing prepupae or adults in preparation for the winter. Bee species that emerge in the spring overwinter as diapausing adults (e.g., mason bees, mining bees, and cellophane bees). In contrast, species that emerge in the summer overwinter as prepupa (a.k.a. diapausing larvae) and complete their metamorphosis to the adult stage during the spring or early summer (e.g., squash bees).

Figure 3. (Left) Cellophane bee - spring (Margarita López-Uribe, Penn State). (Center) Mason bee - spring (David Biddinger, Penn State). (Right) Squash bee - summer (Margarita López-Uribe, Penn State).

Bees use diverse overwintering strategies that involve complex biological processes triggered by environmental cues such as changes in photoperiod and temperature fluctuations. With the rapid changes in climatic patterns across the globe, some of these cues may change in a way that can interfere with the overwintering process of these pollinators. Recent studies indicate that warmer winters can prevent bees from completely shutting down their metabolism during diapause, which may cause them to spend more of their energy reserves. These changes may result in smaller bees the following year. You can still help bees during the winter by providing good habitat for their nests and overwintering places such as twigs, leaves, and logs. Overwintering is a critical step in the life cycle of bee pollinators, so providing this habitat during the winter is as important as providing floral resources during spring, summer, and fall.

For more information about overwintering and the life cycle of bees, check these other resources:

• Boyle N, Cressman A, Amsalem E. 2021. The Bumble Bee Lifestyle. Penn State Extension.
• Brochu KK, Fleischer SJ, and López-Uribe MM. 2021. Biology of the squash bee, Eucera (Peponapis) pruinosa. Penn State Extension.
• Döke MA, Frazier M, Grozinger, CM. (2015). Overwintering honey bees: Biology and management. Current Opinion in Insect Science 10: 185–193.
• Grozinger CM, Anton K. Honey Bee Management Throughout the Seasons. Penn State Extension.
• López-Uribe MM. Spring Bees: Who Are They and Where Do They Live? Penn State Extension.