Despite popular belief, bees do not hibernate in the winter. They remain active all season long. Bees cannot fly when the outside temperature drops below 55°. When it gets below 50°, they crowd into the central area of the hive and form a “winter cluster.” The colder the outside temperature, the tighter the cluster becomes. The exterior circumference of the cluster is 46° to 48°. The interior of the honeybee huddle is kept at a constant 80° and sometimes up to 93°. When the girls on the outside edge of the cluster become cold, they rotate into the center and are replaced by the interior bees. In the middle of this group hug resides the queen and sometimes, a small amount of brood. The sole purpose of the winter bees is to keep their queen and brood warm and safe. They actively generate heat by vibrating their wing muscles. A byproduct is moisture. It may seem counterintuitive, but the smart beekeeper vents the top of the hive so moisture can escape. Bees can survive cold with enough stored honey, but they cannot escape the moisture and humidity laden fungi, disease organisms and molds that survive in this environment.
If the outside temperature rises or the hive is warmed on a sunny day, the entire cluster will move within the hive to stay in reach of their honey stores. The bees in the interior of the cluster will beg for nourishment. The workers at the circumference will access the honey and pass it from bee to bee until the begging signals stop. An individual bee never hoards her honey, but always shares with her sisters. If there is a continued, severe cold front and the cluster cannot move, it is not uncommon for a strong winter cluster to die of starvation within an inch of its honey stores – They share with one another or quickly starve and perish as one entity.
It was 18° tonight when this thermal photo was taken. The FLIR image shows hives #1 and #2 with good heat signatures. Both hives came into the winter with strong, healthy bees. Despite the outside temperature, hive #1 seems to have dispersed bees throughout the hive. Hive #2 has the typical heat signature of a strong winter cluster. My only concern is that it is high in the hive box. Bees follow the heat and honey stores up. They’re very near the top and will have no place to go except to either side. I hope they don’t run out of honey.