Saturday, January 19, 2013

Regulating Hive Temperature

A beekeeper in Minnesota is carefully measuring the temperature inside his bee hives. He recorded a daytime temperature of 70 degrees Fahrenheit and a nighttime temperature of 38 degrees. He asks me what I think of the temperature differences, and he asks if I feel that there is a problem. While Minnesota experiences extremely cold winters, honey bees are very capable of regulating the atmosphere of their hive. They also employ measures to conserve energy and food reserves necessary to survive harsh northern winters. First, they do not attempt to warm their entire hive, only the bees and brood. The bees form a cluster to generate and conserve warmth. Loosely packed bees inside the cluster generate heat by eating their high-energy food, honey, and “shivering” their flight muscles. These bees can create about 104 degrees in their muscle tissue. Bees on the outside of the cluster form a tightly packed crust to hold in the generated heat. As bees on the outside chill, bees from the inside change places with them. The bees are not wasteful of honey stores needed to feed the workers generating heat. They do not attempt to warm the entire hive, just the cluster of bees.

The bees’ second honey conservation effort involves lowering the cluster temperature whenever there is no brood present. Brood must be kept warmer than adult bees. Brood is held at 95 degrees Fahrenheit. A number of races of bees, especially those originating in northern Europe and Asia, restrict the feeding of their queen to force her to stop laying eggs in the winter. When the colony is not tending brood, it lowers its colony cluster temperature to around 70 degrees, the daytime temperature measured in the Minnesota hive. The temperature of the hive outside the cluster drops at nighttime. In today’s photo, we see bees gathering granulated sugar that I placed for emergency feeding atop a hive’s inner cover. Bees access the sugar through the inner cover’s center hole.

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