The question of whether bees hibernate depends entirely on the species. True hibernation is a state of deep dormancy characterized by a significant metabolic slowdown, a lowered heart rate, and a reduced body temperature that closely matches the external environment. This survival strategy conserves energy when food is scarce and temperatures are low. Bee winter survival methods fall into two categories, neither of which perfectly aligns with the textbook definition of mammalian hibernation.
The Social Bee Strategy
Social bees, particularly the Western honey bee (Apis mellifera), do not hibernate. They survive the winter collectively by engaging in a behavior known as clustering, which is a form of social thermoregulation. This strategy requires the colony to remain active and maintain a warm internal temperature regardless of the external cold.
When temperatures inside the hive drop to approximately 57°F (14°C), the worker bees form a tight, spherical mass to conserve heat. The queen remains safely protected near the center of this sphere, where the temperature is actively maintained. Worker bees generate the necessary warmth by vibrating or “shivering” their powerful flight muscles without moving their wings.
The cluster has a dense outer mantle and a looser inner core. Bees in the outer mantle pack tightly together, heads facing inward, to create an insulating shell, which can be as low as 46–65°F (8–18°C). The core bees are responsible for generating heat and maintaining a core temperature of 68°F (20°C) or higher. As the winter progresses, the entire cluster slowly shifts its position to access and consume the vast stores of honey accumulated over the warmer months.
Solitary Bee Survival
The survival strategy of solitary bees, such as mason bees (Osmia) and leafcutter bees (Megachile), is closer to true dormancy. These bees utilize a programmed state called diapause, which involves a developmental or reproductive arrest. Unlike the honey bee colony, the worker bees and males of these species die off completely as cold weather approaches.
In solitary species, the young bee typically enters diapause as a post-feeding larva or prepupa, sealed inside its natal brood cell. The mated bumblebee queen also seeks out a sheltered location, often underground, to spend the winter alone. During diapause, the bee’s metabolism slows significantly to conserve energy reserves.
To prevent freezing, these diapausing bees physiologically prepare by producing high concentrations of cryoprotectants, such as glycerol, in their body fluids. This substance acts like an anti-freeze, lowering the internal freezing point of their cells to survive sub-zero temperatures. The prepupae of the alfalfa leafcutting bee, for example, overwinter with copious quantities of internal lipids, which fuel their minimal metabolic needs during this long, dormant phase.
Timing and Triggers
The initiation of winter survival strategies is governed by predictive environmental cues, allowing the bees to prepare in advance. The most reliable trigger is the decreasing photoperiod, which signals the end of the foraging season. This change is often combined with a sustained drop in ambient temperatures.
For the honey bee colony, these cues prompt a reduction of brood production, allowing the colony to conserve food and produce a generation of long-lived “winter bees.” Solitary female bees respond by provisioning their nests with offspring programmed to enter diapause. This careful timing ensures survival until the spring bloom allows for renewed activity.