Winter bee mortality is one of the most pressing problems facing modern beekeeping. The number of hives that do not survive the winter months has remained at an average of around 28.7 percent since 2006-2007. Some bees do die in winter, but the survival mechanisms of healthy colonies allow families to survive the cold months.
Why do some bees die in winter?
Yes, unfortunately, some colonies inevitably die in winter. This can happen if the population is not large enough, food supplies are insufficient, or the colony enters winter with disease or a virus.
Cold is not the main cause of bee deaths
The physiology of bees is such that at temperatures below 10°C their activity decreases sharply, and at temperatures close to 0°C they fall into a state of torpor. However, this is not the main cause of winter mortality.
The most common mistake made by novice beekeepers is to think that bees die from the cold. In reality, a healthy colony is capable of maintaining a temperature of up to 35°C in the hive, even when the temperature outside drops to -30°C. The main cause of death is quite different.
Shortage of feed supplies
Honey bees will die if they do not have enough food stored in the hive. An average-sized colony needs 25-30 kg of honey to survive the winter. If there is not enough food, the bees will start to starve as early as January-February, when there is no natural nectar flow yet.
Diseases and parasites
Varroasis, nosematosis, and other diseases significantly weaken colonies before wintering. Bees affected by disease have a reduced lifespan and are unable to effectively maintain the thermal regime in the cluster.
A weak colony
Colonies with fewer than 15-20 thousand individuals are physically incapable of forming a sufficiently dense winter club to maintain the necessary temperature throughout the winter.
How do healthy bee colonies survive?
Despite sub-zero temperatures and a lack of flowers, honey bees survive the winter thanks to their amazing set of survival mechanisms. Unlike other insects, honey bees do not hibernate in winter. Instead, they remain active throughout the winter inside the hive, gathered in a cluster.
Formation of a winter club
With the onset of winter, bee colonies go into high gear to prepare for the harsh months ahead. One of the most important strategies they employ is clustering inside their hives. The winter cluster is a dense cluster of bees, where the outer layer forms a protective shell and the temperature inside is maintained at 14-25°C.
Features of winter bees
In summer, worker bees have an average lifespan of about six weeks. The first three weeks are spent working in the hive, and the rest of their lives are spent collecting nectar and pollen. Winter bees are radically different from summer bees:
• Their lifespan increases to 6-8 months
• Their fat bodies contain more nutrients
• Their glands are less active and their metabolism is slower
• Their protein reserves are increased
| Characteristics | Summer bees | Winter bees |
| Life expectancy | 35-45 days | 150-200 days |
| Gland activity | High | Minimum |
| Fat body | 2-3% by weight | 8-12% by weight |
| Protein reserves | Low | High |
Statistics on winter bee mortality by region
The level of winter losses among bee colonies varies significantly across geographical regions and depends on climatic conditions, beekeeping practices, and the prevalence of diseases.
Data for Europe
The level of winter losses of bee colonies ranged from 8.1% to 28.4% in Austria and from 6.4% to 19.4% in the Czech Republic. The overall level of winter losses of colonies was 16.7% and varied significantly between countries, ranging from 5.8% to 32.0%.
The situation in the United States
An annual survey of American beekeepers shows that last winter’s colony mortality rate—nearly 40%—was the highest since the survey began 13 years ago. More recent data points to an even more alarming trend: honeybee mortality in the US has reached record highs, with beekeepers reporting an average loss of 62% of their colonies over the winter.
High losses in the US are due not only to climate factors, but also to intensive pesticide use, monoculture agriculture and stress from migratory beekeeping. European countries with stricter chemical regulation show consistently better results
| Region | Average losses (%) | Loss range (%) |
| Europe (general) | 16,7 | 5,8 – 32,0 |
| Austria | 18,3 | 8,1 – 28,4 |
| Czech Republic | 12,9 | 6,4 – 19,4 |
| United States | 38-62 | 23,1 – 62,0 |
| Россия | 15-25 | 10,0 – 40,0 |
Does climate change affect winter mortality?
Global climate change poses new challenges for bee overwintering. Unstable temperatures, frequent thaws, and sudden cold snaps disrupt the natural biorhythms of bee colonies.
Temperature anomalies and their consequences
Sudden temperature changes cause bees to disrupt the structure of their winter cluster, leading to increased consumption of food reserves. At temperatures above 8-10°C, bees become active and may even perform cleansing flights, expending precious energy.
Disruption of natural cycles
Warm winters stimulate the queen to lay eggs prematurely, which places an additional burden on the colony at a time when food is limited and there is no honey yet.
Biological mechanisms of winter adaptation
Physiological changes
Bees begin their transition to winter mode at the end of summer. Physiological preparation includes accumulating fat and protein reserves, changing hormone levels, and restructuring metabolism.
Winter mode
- Thermoregulation of the cluster: Bees maintain a temperature of 14-25°C in the center of the cluster by contracting their muscles without flapping their wings – thermogenesis.
- Rotation within the cluster: Bees on the outer shell of the cluster periodically switch places with those inside, ensuring uniform heating of the entire colony.
- Oxygen regime: The winter cluster maintains a special ventilation system – carbon dioxide accumulates at the bottom of the hive, creating a “carbon dioxide cushion” that further slows down metabolism.
- Humidity control: Bees regulate humidity in the club through respiration and evaporation, preventing condensation.
- Energy conservation: During winter dormancy, the heart rate of bees decreases from 300 to 150 beats per minute.
Why don’t all types of bees survive winter in the same way?
Wintering strategies vary dramatically between bee species. The queen bumblebee finds a suitable place to hibernate (often underground), ready to wake up in spring and start the cycle again. The queen is the only bumblebee that survives throughout the year for this purpose—all males and worker bees die.
Honey bees (Apis mellifera)
The only species that survives the winter as a whole family. They form a winter club, maintaining activity and temperature control throughout the cold months.
Bumblebees (Bombus spp.)
Young fertilized queens overwinter in a state of diapause in shelters. Worker bees and males die with the onset of cold weather. In spring, the queens that have overwintered establish new colonies.
Solitary bees
Most species spend the winter in the pupal or larval stage in special cells. Adults die in the fall.
Understanding the differences in how different species of bees hibernate is critical to preserving biodiversity. Honey bees are just one species among more than 20,000 species of bees in the world, and each has its own unique survival strategy.
Factors affecting the success of wintering
Colony size
Large beekeeping operations with more than 50 colonies experienced significantly lower losses (p < 0.001). This is explained not only by a professional approach, but also by the possibility of combining weak colonies and redistributing resources.
Quality of the queen bee
Young queens born in 2022-2023 show the best wintering results due to high egg laying during the winter bee build-up period and a lower likelihood of disease.
Forage base
The availability of sufficient feed reserves has a significant impact on wintering.
Sanitary condition
Treatment for varroasis should be carried out no later than September so that winter bees are already healthy. A mite level above 5-7% virtually guarantees the death of the colony in winter.
Can beekeepers prevent winter mortality?
Modern beekeeping methods can significantly reduce winter losses, but it is impossible to eliminate them completely due to natural factors and unforeseen circumstances.
Winter preparation
Successful wintering begins in summer with the formation of strong colonies and the creation of optimal food reserves. The critical period is August-September, when winter bees are raised.
Advanced technologies
The use of insulated hives, humidity control, and monitoring systems allows for optimal wintering conditions to be maintained. Thermal chambers and temperature sensors make it possible to monitor the condition of colonies without interference.
Limitations of intervention
Some beekeepers advocate allowing all bees to die in winter. They have calculated that honey is worth more than bees, so they do not try to keep their bees alive during winter. This approach makes economic sense in regions where bee colonies are cheap, but it is unacceptable from the point of view of sustainable beekeeping.
Conclusion
Winter bee mortality is a complex phenomenon that cannot be explained by a single cause. Healthy, properly prepared colonies are able to successfully survive even harsh winters, while colonies weakened by disease or improper care die even in relatively mild conditions. Understanding the biological mechanisms of wintering and risk factors allows beekeepers to significantly reduce losses and ensure the sustainable development of their apiaries. Modern science provides sufficient knowledge for successful wintering, but its practical application requires experience and constant attention to the condition of bee colonies.
FAQ
Yes, some bees and entire colonies do die during winter. The average winter loss rate is 15-30%, depending on the region. The main reasons are lack of food, disease, and colonies that are too small to maintain their temperature.
Negative temperatures alone do not kill bees. A healthy colony maintains a temperature of 14-25°C in its winter cluster even when the outside temperature drops to -30°C. The situation becomes critical when the colony is unable to maintain its cluster due to low numbers or depleted food reserves.
An average-sized colony needs 25-30 kg of honey to successfully overwinter. The minimum reserve is 20 kg, but this amount may not be sufficient in the event of a prolonged winter or early colony activity in spring.
Feeding in winter is highly undesirable and can lead to the death of the colony. Winter bees are unable to process syrup, and attempting to feed it disrupts the structure of the cluster and activates the bees at an inappropriate time.
Survival depends on several key factors: the strength of the colony before wintering (at least 15-20 thousand individuals), sufficient food reserves, absence of diseases (especially varroasis), and the quality of the queen. Colonies that enter winter weakened have minimal chances of survival.
Winter bees are radically different from summer bees: they live for 6-8 months instead of 35-45 days, have increased fat reserves (8-12% of their body weight compared to 2-3%), reduced gland activity, and large protein reserves. These adaptations allow them to survive long periods without food.
Honey bees are the only species that hibernate as a whole colony. Bumblebees survive the winter only as young queens, which establish new colonies in the spring. Solitary bees hibernate in the larval or pupal stage, while adults die in the fall.
