Agriculture Reference
In-Depth Information
Roughly in the center (top to bottom, sides to sides) of a three-box, eight-frame
hive is the broodnest portion of the colony. When the outside temperature drops
below 57°F (14°C), the bees congregate in the broodnest area. They crawl into
some of the empty cells and fill the spaces between combs. Separated by thin wax
walls, this fairly compact mass of bees is called the winter cluster.
The winter cluster is like a ball of bees—the outside layer of the ball is com-
posed of bees tightly packed together and acting as an insulating layer, with their
heads facing toward the center of the mass. Nearer the center, the concentration of
bees isn't quite as dense, so interior bees can move a bit to get food or care for any
brood present.
The temperature required to raise brood is about 95°F (35°C), so the bees in the
cluster vibrate their wing muscles to generate heat. As they exercise, their body
temperature increases and the generated heat expands outward to help the layer of
insulating bees keep warm. These bees, too, vibrate their wing muscles to generate
heat and to keep warm. At the very edge of the cluster the temperature reaches but
does not fall below 45°F (7°C).
Obviously, the bees on the very outside of this cluster cannot sustain themselves
for long at that temperature, so they gradually move toward the center, and the
warm, well-fed bees from the inside move toward the outside to replace them.
If the outside temperature falls below 57°F (14°C), the cluster begins to reduce
its size, shrinking uniformly. This action reduces the surface area of the ball, and
the bees in the insulating layer move even closer together, reducing heat loss from
the interior and forming dead air spaces between their bodies. As the temperature
drops more, the ball continues to shrink, until it becomes a solid mass of bees. This
configuration can be maintained for a short time, but eventually the bees in center,
nearest the food, will have consumed all of the honey they can reach.
Bees do not warm the entire inside volume of the colony. All the space around
the cluster—above, below, and to the sides—remains at exactly the ambient tem-
perature outside the hive. The only warmth generated is kept in the cluster and is
not wasted on empty space. This concentration of warmth is efficient from a heat-
conservation perspective, but there is a downside. When the outside temperature
becomes very cold, the cluster cannot move to reach more food. If the temperature
remains very cold for a long time (less than about 20°F (-7°C), the bees will starve
when the food inside the cluster is gone.
When the outside temperature warms, however, the outer insulating layer of
bees expands, and the volume of the cluster expands with it, moving to frames with
stored honey on the sides of the broodnest or above it.
 
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