The Thermology of Wintering Honey Bee Colonies - Charles D. Owens 1971

  • A colony protected by insulation will have a less compact cluster that will fluctuate more in size with temperature changes than a cluster in an unprotected colony
  • Insulated colonies start brood rearing a few days earlier than unprotected colonies but the latter tend to catch up shortly after warmer weather arrives
  • A cluster held for long periods under freezing conditions declines in strength. The rate of decline is dependent on pollen stores available, but is slower in insulated than unprotected colonies.
  • Brood rearing will occur under sub-zero conditions in insulated colonies with plenty of pollen and honey stores in the cluster.

The Honey Bee Cluster as a Homeothermic Superorganism - Edward E. Southwick 1982

  • Intact clusters of 10-20,000 bees increase metabolism when exposed to cold environmental temperatures
  • Below 10C (50F) metabolic rate increases as a function of decreasing ambient temperature
  • At moderate ambient temperatures (10C to 14C) (50F to 57F) the cluster "breaks" resulting in a massive increase in total surface area for heat exchange and resulting in large increases in metabolism
  • Low rates of metabolism at night when the cluster was tightly packed. At midday, the cluster broke resulting in 2.5 times increase in metabolism to 25.7 Watts/Kg

Metabolic Energy of Intact Honey Bee Colonies - Edward E. Southwick 1981

  • Minimal rates of metabolism (as low as 3.4 Watts/Kg were usually reached at night and maximum rates (as high as 33.5 Watts /Kg around midday
  • Bees in the central core of the cluster generate heat from thoracic muscle work and metabolism of food stores, and an outer shell of living bees acts as an insulating layer
  • Cluster core temp remains high (circa 33C) at cold ambient temperatures and stable as the cluster contracts thus reducing the surface area for convective and radiative heat loss
  • Values obtained for heat production of intact colonies at 10-20C (50-68F) averaged 25.7 Watts/Kg in the day and 10.1 Watts/Kg at night
  • Metabolic heat production is increased greatly as the temperature differential between the inside of the core and the outside of the outer cluster increases from 2C to 9C (4F to 16F)

If you are interested in learning more we suggest you take a look at the Canadian Association of Professional Apiculturists' excellent overview on the Wintering and Management of Colonies in Winter