In temperate areas of the United States, overwintering honey bees is a constant challenge. Collective wisdom deemed it of utmost importance to insulate the beehive against cold. To this end, beekeepers have tried a variety of techniques including surrounding colonies with hay, straw, tar paper, styrofoam or fiberglas batt insulation.1
Wrapping colonies in this manner was no doubt influenced by those who believed bees were attempting to heat the interior of their hive as human beings do houses. This is only partially the case. The bees really only attempt to warm a discrete cluster of individuals within the hive. The cluster begins to form at 57 degrees Farenheit; it is made up of an inside population covered by an insulating layer(s) of individual worker bees. Further insulating by beekeepers can bring on other problems. Of major significance is that the air, warmed by the bees and trapped inside a tightly wrapped colony, is full of moisture.
Experience indicates that damp air is more detrimental to honey bee colonies in winter than cold temperatures. In cooler reaches of the colony, moisture can condense and may even drip back onto the insulating layer of workers surrounding the cluster.
Although the bees do a good job of keeping colonies ventilated during the active season, they cannot do so while clustering at low temperatures. Two common methods to promote air circulation by beekeepers, therefore, are to prop up the cover with wooden wedges and/or bore holes in the front of supers.
In summary, insulation is not as important as venting excess moisture in cold weather. This is even true in southern climes where high humidity levels may lead to growth of various fungi such as the organism responsible for chalkbrood. The need for adequate ventilation is also important during nectar flows. Swarming is also reduced by this process.
Providing upward ventilation for colonies is universally good beekeeping practice.See contributor Rusty Burlew’s comments on keeping honey bees dry and draft free. However, she says care must always be exercised to provide for maximum ventilation with minimum exposure to robbers.
1 D. Murrell and D. MacDonald, The Alberta Beekeeping Manual, Agdex 616-4, Alberta Department of Agriculture, pp. 57-58, 1983.