How do bees survive winter?
What do bees do during winter? It’s a common question, and the answer varies wildly between bee species. Bees have unique adaptation methods to help them survive from year to year. Wisconsin's native bees have developed ingenious strategies to withstand the harsh winter conditions, whereas honeybees form perennial colonies and hibernate as a group. Some species of bumblebee employ a similar communal approach by clustering together within their nests to generate warmth. This spectrum of adaptations exemplifies the resourcefulness of native bees in navigating the challenges posed by winter.
Native Bees:
Many native bee species are solitary, with each female constructing her own nest. To endure the temperatures, these solitary bees often seek refuge in underground burrows or natural cavities, creating a protective environment insulated from the cold. Native bees undergo physiological changes to endure the winter months by entering a state of dormancy known as diapause, slowing down their metabolic activity to conserve energy.
Bumble Bees:
In the United States, there are approximately 49 species of bumblebee. Their biology differs depending on the climate and habitat of their endemic range. In general, bumbles have an annual life cycle. Bumblebees do not dig their nests or cause property damage like wasps and carpenter bees (that are known to eat/chew wood). Bumbles will often nest in pre-existing cavities that provide insulation and protection from the elements. Things like old rodent burrows, grass bunches, compost piles, hollow logs, or large roots provide them shelter during the winter, along with man-made structures like birdhouses.
Understanding their life cycle helps us understand how they can survive winter. Bumblebees have a social structure with overlapping generations and cooperative care for the brood. Queens are the only survivors during winter. The queens will emerge from hibernation each spring and spend the next few weeks foraging and looking for a new home. The next several weeks are spent gathering resources to fuel their egg-laying process. Like caterpillars, bumblebees undergo a complete metamorphosis from larva to fuzzy adulthood in 4-5 weeks. Colonies reach their peak size in summer. When there are enough workers to take over foraging responsibilities, the queen focuses on creating males and queens for the following year. Males and young queens leave the nest to mate, with only the queen returning. This is why we can often find male bumblebees sleeping on vegetation in late summer. Young queens that have mated will spend the rest of the year preparing for diapause- foraging to build up fat reserves while looking for a safe place to overwinter. Once a suitable location is found, they hunker down and enter a hibernation-like state and will remain there until spring to repeat the cycle.
Honeybees:
Honeybees have a completely different strategy for overwintering. They must provide their own heat source and maintain a food supply inside the hive to make it to spring. Honeybees will huddle up around the queen, creating a tight cluster inside the hive. The worker bees will vibrate their bodies to generate heat. Their communal goal is to keep the hive warm enough for the queen and colony to survive. The combined heat of all the workers can create a core temperature of 90 degrees! The cluster has two parts: a much denser outer mantle and a looser inner core. It takes an immense amount of energy to vibrate all winter long, so they must build up a large reserve of honey to keep them energized enough to ensure the colony survives. Because the hive is not growing throughout winter, male drones are a needless drain on winter resources and are kicked out in late fall. New males will be created the following year. On warm winter days (55 degrees or warmer), honeybees may forage from nearby bird feeders for tiny bits of protein.
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