Bees, often associated with warm, sunny days and blooming flowers, face significant challenges as temperatures drop. The question of whether bees survive the winter has a nuanced answer: yes, but their strategies vary considerably depending on the species. While some bee species endure the cold as a collective, others rely on individual survival mechanisms or overwinter in different life stages. This diversity in winter survival highlights the remarkable adaptability of bee populations to seasonal changes.
Honey Bee Winter Survival
Honey bees (Apis mellifera) employ a unique and highly social strategy to survive winter. Instead of hibernating, the entire colony remains active inside the hive, forming a dense cluster when outside temperatures fall below 50-57°F (10-14°C). This winter cluster functions as a living furnace, generating and conserving heat.
Worker bees, particularly a specialized caste of “winter bees” born in the fall, play a central role. They shiver their flight muscles without moving their wings, generating heat. This muscle vibration burns stored honey, their primary fuel source. The cluster maintains a core temperature of approximately 90-100°F (32-37°C), especially around the queen and any developing brood, while the outer mantle of bees insulates the core.
The queen bee is typically at the warm center of this cluster, largely ceasing egg-laying during winter to conserve resources. Bees in the cluster slowly move across the honeycombs, consuming honey to ensure continuous access to food. If the cluster loses contact with its honey supply, the colony can quickly starve. This collective thermoregulation allows honey bee colonies to persist through prolonged cold.
Winter Strategies of Other Bee Species
While honey bees cluster, many other bee species adopt individual rather than colonial strategies to survive winter. Bumble bees, for instance, do not overwinter as a colony; only newly mated queens survive the cold season. These queens find sheltered locations, such as burrows in the soil, leaf litter, or wood piles, where they enter a state of hibernation.
During this solitary hibernation, the queen bumble bee produces a chemical, like glycerol, to prevent freezing and relies on fat reserves accumulated in the autumn. She emerges in the spring to establish a new colony. This individual survival mechanism contrasts sharply with the honey bee’s collective effort.
Solitary bees, which do not live in colonies, have diverse overwintering strategies. Many overwinter as larvae or pupae within protected nests. These nests might be located in hollow plant stems, tunnels in the ground, or small holes in wood. They remain in a dormant state in these sheltered locations until conditions become favorable for their emergence in the spring.
Winter Challenges for Bees
Winter presents a difficult period for all bee species due to several environmental and biological factors. A primary challenge is the scarcity of food sources, as nectar and pollen-producing flowers are generally absent during colder months. Honey bees rely on their stored honey, while other species depend on fat reserves or early spring blooms upon emergence.
Extreme cold itself poses a direct threat. While honey bee clusters generate heat, smaller colonies or those in poorly insulated hives may struggle to maintain sufficient warmth. Wind chill can also be particularly harmful, increasing heat loss from hives.
Diseases and parasites also contribute to winter mortality. Varroa mites are a notable threat to honey bee colonies, weakening individual bees and transmitting viruses. Colonies with high mite loads entering winter are less likely to survive, as the mites compromise the health of the “winter bees” crucial for colony thermoregulation. Pesticide exposure can further exacerbate these challenges, as bees may encounter residues or bring contaminated resources back to the hive, weakening them before the cold season.
How Humans Can Help Bees in Winter
Individuals can take several steps to support bees during the winter months. One effective action involves modifying garden cleanup practices. Leaving fallen leaves and dead plant stems in garden beds provides essential shelter and nesting sites for overwintering solitary bees and hibernating bumble bee queens. Leaving natural debris in gardens can offer these bees suitable overwintering sites.
Planting winter-flowering plants can offer crucial early-season food sources for bees that emerge on warmer winter days or in early spring. Species like hellebores, winter heath, snowdrops, and certain varieties of crocus and mahonia can provide nectar and pollen when other sources are scarce.
Reducing pesticide use is another important measure, particularly avoiding applications when plants are blooming or when bees are active. Applying pesticides in the evening, when bees are less active, can help minimize their exposure. For honey bees, responsible beekeeping practices include ensuring colonies have ample honey stores for winter and monitoring for and treating Varroa mites before the cold sets in. Providing sheltered locations for hives, such as with windbreaks or insulation, can also improve their chances of survival.