How honey bees keep warm in winter?

How hard is winter on honey bees and when it gets really cold, can bees die? Is there anything we can do to help our bees survive a harsh winter? Find out how honey bees keep their hives warm even though they are cold-blooded.

Up until only a few years ago, it was thought by many scientists that Honey beehives were kept warm by pupae in the brood and that the bees would often congregate there to warm themselves up from the pupae.

Recently, this was found not to be the case when a new Honey bee job was discovered, that of “heater bees.”  Bees of almost all ages can perform this function by either vibrating their abdomens or they can also decouple their wings from their muscles, allowing them to vigorously use these muscles without actually moving their wings.  This can heat their bodies up to about 111° Fahrenheit (44° C), which is about 16° F (9° C) hotter than their normal body temperature.

Normally, Honey bee jobs are primarily “assigned” based on their age.  However, if the hive needs more bees that are naturally inclined towards housekeeping jobs or foraging, the heater bees can adjust the temperature of certain cells to accommodate this.  Raising the temperature of a cell to 95° F (35° C) rather than the normal cell temperature of about 93° F (34° C) will produce bees that are more inclined to prefer foraging jobs, over housekeeping ones, and vice-versa; so they’ll be more reluctant or more eager to change jobs than other bees their age, depending on their former cell temperature.  This helps make sure that the needs of the colony can always be met given the current state of the hive and environment.

How hard is winter on honey bees? When it gets really cold, can bees die?

During winter, the bees all clump together towards the middle of the hive, surrounding the queen.  At this time, they allow the temperature of the hive to drop to around 81° F (27° C) on the inside of the cluster to conserve energy. Bees on the outer parts of the cluster, which will usually be around 48° F (9° C), then occasionally rotate with the bees on the more crowded inner parts, so that all the bees can keep warm enough to survive. Once the queen starts laying again, the temperature of the inner part of the hive will be raised back up to about 93° F (34° C).

Most bees and wasps hibernate during the colder months. In many species, only the queen survives the winter, emerging in spring to reestablish a colony. But honey bees remain active all winter long, despite the freezing temperatures and lack of flowers on which to forage.

The honey bee colony’s ability to survive the winter depends on their food stores. Keeping warm takes energy in the form of honey.

If the colony runs short of honey, it will freeze to death before spring. The worker bees force the now useless drones from the hive, leaving them to starve. It’s a harsh sentence, but one that’s necessary for the colony’s survival. Drones would eat too much of the precious honey, and put the hive in peril.

The honey bee workers form a cluster around the queen and brood, keeping them warm. They keep their heads pointed inward. Bees on the inside of the cluster can feed on the stored honey. The outer layer of workers insulates their sisters inside the sphere of honey bees. As ambient temperatures rise, the bees on the outside of the group separate a bit, to allow more airflow. As temperatures fall, the cluster tightens, and the outer workers pull together.

As it gets colder, the worker bees actively generate heat within the hive. First, they feed on honey for energy. Then, the honey bees shiver. They vibrate their flight muscles but keep their wings still, raising their body temperatures. With thousands of bees shivering constantly, the temperature at the center of the cluster will warm up considerably, to about 93° F! When the workers on the outer edge of the cluster get cold, they push to the center of the group, and other bees take a turn shielding the group from the winter weather.

During warmer spells, the entire sphere of bees will move within the hive, positioning themselves around fresh honey stores.

Sources:
http://insects.about.com/od/antsbeeswasps/qt/How-Honey-Bees-Keep-Warm-In-Winter.htm
http://www.dummies.com/how-to/content/how-to-keep-a-beehive-in-the-winter.html
http://basicbeekeeping.blogspot.hr/2009/01/lesson-46-how-hard-is-winter-on-honey.html
http://www.todayifoundout.com/index.php/2012/06/how-honey-bees-keep-their-hives-warm-given-that-they-are-cold-blooded/
Image: http://blog.brushymountainbeefarm.com/2014/11/helping-your-hives-in-winter.html