Tag Archive | heat

Winter Clusters – How Bees Stay Warm

I’m amazed at how hardy bees are in the cold.  Usually bees die in the winter due to varroa, nosema, condensation, and other factors.  Here’s an interesting explanation from HoneyBeeSuite about winter clusters and how the bees stay alive during the cold weather.

The cluster stays warm, the hive does not

Natural systems do not waste energy and honey bees are no exception. To survive the winter, a cluster of bees must keep itself warm. While it does this efficiently, it makes no attempt to heat the entire space within the hive.

The warmest place within a hive is in the center of the cluster. The temperature of the cluster decreases as you move toward the outside. The bees on the outside get so cold that they must rotate to the inside. If the inside of the hive were uniformly warm, this rotation would be unnecessary.

Of course, there is some heat lost from the cluster into the surrounding air, and because heat is lost, the bees must continually generate more. If you put your hand close to a heated iron, for example, you can feel the heat. The heat loss from the iron is similar to the heat loss from the cluster. You don’t have to move far away before you no longer feel it. The same is true inside the hive: the temperature drops rapidly as you move away from the cluster.

Nevertheless, the air inside the hive is slightly warmer than the ambient outside air. This is because the hive box itself provides a small amount of insulation. But the R-value of a pine board is not much, which means the difference in temperature between the inside air and the outside air is not great.

Heat rises from the cluster

There is one place in the hive that is warmer than the others, and that is the space immediately above the cluster. That is because warm air rises. One beekeeper in France measured the temperatures in his hive when the outside air temperature was 44°F. He measured 95° in the center of the cluster, 71° immediately above the cluster and 52° in other empty portions of the hive. Other beekeepers have found similar temperature gradients.

For this reason, an insulating layer placed above the bees reduces the rate of heat loss from the hive. Styrofoam, wood chips, or a layer of another material will slow the loss through the roof. But even this has its limits. For one thing, as the internal temperature gets warmer in comparison to the outside air, more heat is lost through the walls, so overhead insulation alone does not conserve as much heat as insulating the top and sides. It is a complex system with no easy answers.

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Breaking the Cluster

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Winter Newbie Mistake – January 5, 2014, Sunday

With a forecast of sub-freezing wind chill temps nearing, I got anxious about adding a solid bottom board to Blue Hive 3 (BH3).  Keep in mind, temps were still darn cold – 30’s and 40’s.  I did add mite boards in the bottom of Green Hive (GH1) and Yellow Hive (YH2) to close off any bottom drafts, but those hives are larger and stronger.  BH3 is a little guy that so far (knocking on wood) has survived this cold snowy winter.

The intent was to lift the hive and slide a board beneath it.  Bad idea.  I pryed the bottom with my hive tool and jostled the top of the hive trying to remove the wind barrier frame.  Suddenly bees began coming out.  I began apologizing and willing them to go back in.  We stopped, put the barrier back and dispersed.  Another lesson learned the hard way.  I thought for sure I’d lose BH3 over this one.

The BH3 Verdict – January 20, 2014, Monday

Our first semi-warm day, mid-50’s, since the jostling incident.  I was on vacation, but the hubster kept watch over the hives and reported that bees were indeed coming out of all three hives, including BH3.  GH1 was going nuts.  Tons of bees out and about relieving themselves.  YH2 was also awake, but not nearly as much activity as GH1.  I never know what to think of YH2.  They’ve never been as active as GH1, and just when I think the worst, they prove me wrong.  Best news – BH3 had bees coming out. Yay!  All three hives are still alive for the time being.  I left them plenty of honey stores, and they still have plenty of candy to supplement their feeding.  I shall leave them alone til our next 50-something degree day.

Lesson learned:  Best to leave the bees alone in cold temps.  Any rapping or tapping on the hive could break the cluster, and breaking the cluster could prove fatal to a hive.