How do honey bees survive our cold winters?
Good question! How can a little cold-blooded insect survive temperatures in the single digits like we’ve experienced this past week? First, let’s talk about what they DON’T do.
- Honey bees do not migrate, as butterflies do.
- Adult honey bees do not die off leaving only the brood to survive the winter, as flies do.
- Honey bees do not come inside your house to keep warm, as Asian ladybugs and stink bugs do.
- Honey bees do not burrow underground for insulation, as Japanese beetles and ants do.
- Honey bees do not hibernate, as yellowjackets, wasps, and hornets do.
So how do honey bees survive the winter? By controlling the temperature of, or thermoregulating, their environment, the hive.
Bees fly freely when ambient temperatures are between 50°F – 110°F and the “cluster” expands and contracts to regulate air flow around each bee. A cluster is a ball of bees surrounding the queen and covering the brood (cells of uncapped eggs, larvae, and capped pupae) to keep it warm. This method is used year round. When the temperature is hot, you will find bees congregating on the outside of the hive to cool off and allow air to flow through the hive. When ambient temperatures drop to 50°F, the bees’ body temperature will drop to about 57°F and they will form a cluster inside the hive to warm themselves and the brood. The lower the temperature, the tighter the cluster. This is very effective most of the year and in temperate winters.
When outside temperatures drop to around 23°F, the bees in the center of the cluster decouple their wings and vibrate their wing muscles, burning calories to generate heat. As long as there is brood, the core temperature of the hive must remain a constant 93°F, so the queen discontinues egg laying during this time. When no brood is present, the internal temperature of the cluster may drop to 55°F and the temperature around the perimeter of the cluster may be as low as 48°F. At a body temperature of 45°F, the bees on the outside become motionless and form an insulation barrier. This state is called “torpor”. Bees in torpor are often mistaken to be dead.
Another way that honey bees regulate the temperature of their hive is through the use of “heater bees”. These bees crawl inside empty cells and vibrate their abdomens, bringing their body temperature up to about 111°F and heating the wax of not only the cell they are in but also those around it. One single heater bee is thought to have the ability to keep up to 70 adjoining cells warm.
To summarize:
Most of the regular activities of honey bees cease in winter, but they do not hibernate. They are able to regulate the temperature of the colony in three ways:
-
- Expanding and contracting the cluster
- Vibrating their wing muscles to generate heat
- Heater bees vibrate their abdomens to heat the surround wax cells
Now you know!
Stayed tuned to learn more about these fascinating little creatures!
References:
- Honey Bee Biology and Beekeeping, Dewey M. Caron with Lawrence John Connor, Wicwas Press, 2013.
- “Bee Cluster, Flying, and Active Temps“, Feb 23, 2009, Bee Hive Journal,
- “What Happens to Bees in Winter?“, Brookfield Farm Bees & Honey Blog, Nov 23, 2010.
- “How Honey Bees Keep Their Hives Warm Given That They Are Cold Blooded“, Daven Hiskey, Today I Found Out, June 30, 2012.