What’s wrong with hives?

For 119 years, the belief that the way honeybees assemble together provides them with a kind of evolutionary isolation has been fundamental to beekeeping practices, hive design, and the study of honeybees. Recently, California beekeepers have even put their bee colonies into cold storage for the summer because they believe this is good for the health of the brood.

But a new study by scientist Derek Mitchell suggests that clumping is a nuisance behavior rather than a benign response to falling temperatures. A conscious encouragement to gregarious bees through certain practices or deliberately shoddy design of beehives is not just Poor care and even cruel treatment of bees.

Honey bee colonies (Apis mellifera) do not hibernate. In the wild, they hibernate in tree cavities where at least some of their numbers are above 18 degrees Celsius, in a wide range of climates, including winters as low as -40 degrees. The problem is that our understanding of hibernation is based on observations of the behavior of these insects in thin wooden hives, the walls of which are 19 millimeters thick. These artificial beehives have very different thermal properties compared to their natural environment (tree cavities with an average wall thickness of 150 millimeters).

On cold days, colonies in thin-walled hives form dense discs of bees called clusters between combs (combs). The center (core) of these disks is less dense and hotter (up to 18 degrees). This is where bees produce the most heat, eat and metabolize sugar from honey. Because bees’ body temperature is very low, the cooler outer layers (mantle) produce very little heat. If the temperature drops below 10 degrees, bees die there.

• Beginning in 1914, beekeeping textbooks and scientific articles stated that the mantle “insulated” the inner core of the hive. For this reason beekeepers began to see clustering as natural and even necessary.
• In the 1930s, this belief was used to justify keeping honeybees in thin-walled hives, even in -30 degree climates.
• This led to the practice in Canada in the late 1960s of keeping honeybees in cold rooms at 4 degrees Celsius to keep them together during the winter months.
• In the 2020s, beekeepers are chilling bees during the summer months to facilitate chemical treatments for parasites. This is happening all over the USA. Outside of cold winter, beekeepers often have to find the queen and put her in a cage if they want to treat a mite infestation. But permanent cold storage bypasses this time-consuming step, making commercial pollination services more profitable.

Scientists were wrong

But this new study found that cluster mantles act more like a heat sink, reducing insulation. Cooping up isn’t about wrapping yourself in a thick blanket to stay warm; rather it is a desperate struggle to get closer to the “fire” or die. The only positive is that the mantle helps keep nearby bees alive.

When the temperature outside the hive drops, the bees around the mantle go into hypothermic mode and stop producing heat. The mantle shrinks when the bees try to keep the temperature above 10 degrees. Bees in the mantle move closer to each other, increasing the thermal conductivity between them and reducing insulation. Heat will always try to move from a hot area to a cold area. The rate of heat flow from the core bees to the mantle bees increases and the bees are best kept outside the mantle at 10 degrees.

Imagine a down jacket – air spaces between the fluff help keep its owner warm. Honeybee clusters resemble the compressive action of a down jacket, with the result that the thermal conductivity increases over time to that of a dense mass of feathers, more like a leather jacket. In contrast, when penguins gather in Antarctica in winter, they all keep their cores warm at the same temperature, and so there is little or no heat exchange between penguins. Unlike bees in the mantle, penguins are not in hypothermic hibernation.
– writes the author of the work.

Scientists and beekeepers did not pay attention to the role played by the invisible layer of air between the hive and the cluster.

The thin wooden walls of commercial hives act as a boundary between the air space and the outside world. This means that the hive walls must have significant insulation, such as 30 millimeters of polystyrene, to be effective.

Failure to understand the complex interplay between the colony body, heat carriers (heat, radiation, water vapor, air), and honeybee behavior and physiology is the result of people not recognizing the hive as an extended honeybee phenotype.