Honeybees in man-made hives may have been suffering the cold unnecessarily for over a century because commercial hive designs are based on erroneous science, my new research shows.
For 119 years, a belief that the way honeybees cluster together gives them a kind of evolutionary insulation has been fundamental for beekeeping practice, hive design and honeybee study. More recently, California beekeepers have even been putting bee colonies into cold storage during summer because they think it is good for brood health.
But my study shows that clustering is a distress behaviour, rather than a benign reaction to falling temperatures. Deliberately inducing clustering by practice or poor hive design may be considered poor welfare or even cruelty, in light of these findings.
Honeybee (Apis mellifera) colonies don’t hibernate. In the wild they overwinter in tree cavities that keep at least some of their numbers above 18 C in a wide range of climates, including -40 C winters. But popular understanding of their overwintering behaviour is dominated by observation of their behaviour in thin (19mm) wooden hives. These man-made hives have very different thermal properties compared with their natural habitat of thick-walled (150mm) tree hollows.
Getting through winter
On cold days in these thin-walled hives, colonies form dense disks of bees, called a cluster, between the honeycombs. The centre of these disks (the core) is less dense and warmer (up to 18 C). This is where the honeybees produce most of the heat by eating and metabolising the sugar from honey. The cooler outer layers (mantle) produce very little heat as the bees’ body temperatures are too low. If the temperature falls much below 10 C, the bees there will die.
Since 1914, beekeeping texts and academic papers have said the mantle “insulates” the inner core of the hive. This meant beekeepers saw clustering as natural or even necessary. This belief was used in the 1930s to justify keeping honey bees in thin-walled hives even in -30 C climates. This led, in the late 1960s in Canada, to a practice of keeping honeybees in cold storage (4 C) to keep them clustered over the winter.
In the 2020s, keepers are refrigerating honeybees in summer to facilitate the chemical treatment of parasites. This is happening across the US for example in Idaho, Washington and Southern California. Outside of a cold winter, if beekeepers want to treat mite infestations, they normally have to locate and cage the queen.
