by Honeybees in man-made hives may have been suffering the cold unnecessarily for over a century because commercial hive designs are based on flawed science, my new research shows.
For the past 119 years, the belief that the way honeybees mate provides them with a form of evolutionary insulation has been fundamental to beekeeping practice, hive design and honeybee study. Recently, California beekeepers are even putting bee colonies in cold storage during the summer because they think it’s good for brood health.
But my study shows that clustering is distressing behavior, rather than a benign reaction to falling temperatures. Therefore, bad welfare or even cruelty from clusters through bad hive design or practice could be considered, in light of these results.
HONEY BEACH (Apis mellifera) colonies do not hibernate. In the wild they hibernate in tree cavities that keep at least some of their numbers above 18°C in a wide range of climates, including wintering at -40°C. But observation of their behavior in thin wooden hives (19mm) is the most common understanding of their winter behavior. These man-made hives have very different thermal properties compared to their natural habitat of thick-walled (150mm) tree hollows.
Getting through the winter
On cold days in these thin-walled hives, compact colonies of bees, called clusters, form between the honeycombs. The center of these discs (the core) is less dense and warmer (up to 18°C). This is where the honey bees produce most of the heat by consuming and metabolizing the sugar in the honey. The cooler outer layers (mantium) produce very little heat because the bees’ body temperatures are too low. If the temperature drops much below 10°C, the bees there will die.
Since 1914, beekeeping texts and academic papers have stated that the inner core of the hive “insulates”. This meant that beekeepers believed that clustering was natural or even necessary. This belief was used in the 1930s to keep honeybees in thin-walled hives even in -30°C climates. As a result of this, in the late 1960s, in Canada, the practice was to keep honey bees in cold storage (4°C) to keep them clustered during the winter.
In the 2020s, keepers are refrigerating honey bees in the summer to facilitate 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 a mite infestation, they usually have to find and cage the queen. But cold storage means that beekeepers can skip this labor-intensive step, making their commercial pollination services more profitable.
Struggling for warmth
However, my study found that a larger mantle cluster acts more like a heatsink, reducing insulation. Huddled together to keep warm is not a thick measure, but more like a desperate struggle to get closer to the “fire” or die. The only downside is that the mantle helps keep the bees alive near the outside.
As the temperature outside the hive drops, bees around the mantle go into hypothermic shutdown and stop producing heat. The mantle compresses as the bees try to stay above 10°C.
The mantle bees increase the thermal conductivity between them and reduce the insulation. Heat will always try to move from a warmer region to a cooler region. The rate of heat flow increases from the core bees to the mantle bees, keeping those bees on the outside of the mantle at (hopefully) 10°C.
Think of a down jacket – it’s the air gap between the feathers that helps keep the person warm. Honey bee clusters resemble the action of compressing a down jacket, whereby the thermal conductivity eventually rises to a feather-dense solid, more like a leather jacket.
In contrast, when penguins are roaming in the Antarctic winter, they all keep their cores warm at similar temperatures, so there is very little heat transfer between the penguins. Unlike the bees in the mantle, there are no penguins in hypothermia.
Academics and beekeepers have forgotten the role played by the invisible air gap between the hive and the cluster. The thin wooden walls of commercial hives act as a boundary between the air gap and the outside world. This means that beehive walls must be efficient, highly insulated, for example 30mm of polystyrene.
This misunderstanding of the complex interplay between colony enclosure, thermophytes (heat, radiation, water vapor, air) and honey bee behavior and physiology has occurred because people do not recognize the hive as the extended phenotype of the honey bee. Other examples of an extended phenotype include a spider’s web and a beaver’s dam.
There are almost no ethical standards for insects. But there is growing evidence that insects feel pain. A 2022 study found that bumblebees react to potentially harmful stimuli in a way similar to pain responses in humans. We urgently need to change beekeeping practice to reduce the frequency and duration of clustering.
This article from The Conversation is republished under a Creative Commons license. Read the original article.
Derek Mitchell does not work for, consult with, own shares in, or receive funding from, and discloses any relevant affiliations with, any company or organization that would benefit from this article beyond his academic appointment.
