Below is a link to what is probably the best study I've read yet about the difference between the hive cavity that honey bees live in in the wild (and therefore what we need to be providing for them) and what we've subjected them to with conventional Langstroth hives. So many of their challenges (including living in symbiotic relationship with Varroa) are either caused, or made worse, by the use of conventional Langstroth hives.
In fact, there's more and more evidence that the winter cluster is not a natural, in-the-wild, behavior of honey bees, but rather a coping mechanism they've had to adopt to survive in Langstroth hives.
The article discusses both insulative qualities and ventilative qualities of the hive cavity. The ventilative qualities that a colony needs are exactly why I've designed the insulated, ventilated inner cover of my Bee Tree Hives so that there is no convection flow directly above the bees, and the bees have the ability to completely control both the amount and route of the ventilation flowing through the hive. And it's not fixed; they can re-open the vents, if they need to, by removing the propolis they used to close them down.
Here's just one little excerpt from the article: "The complication arises from the fact that natural humidity levels change in response to many ordinary variables in the daily life of the colony. Therefore, a fixed amount of applied ventilation will not accommodate those natural fluctuations."
Here's the link to the article: http://www.beeculture.com/winter-management/
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