Honeybees in man-made hives could be exposed to unnecessary cold for more than a century because commercial hive designs are based on flawed science, according to a new study.

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

But my research shows that clustering is a disturbing behavior, not a benign response to cooling. In light of these findings, deliberately encouraging aggregation through practice or poor hive design could be considered poor welfare or even cruelty.

Honey bee colonies (Apis mellifera) do not hibernate. In the wild, they hibernate in tree holes, where at least some of their population survives above 18 °C in a wide range of climates, including -40 °C winters.

However, the general understanding of their behavior during overwintering is shaped by observation of their behavior in thin (19 mm) wooden beehives. These man-made hives have very different thermal properties compared to the natural habitat of thick-walled (150 mm) tree cavities.

get through the winter

On cold days, colonies in these thin-walled hives form dense discs of bees called clusters between the honeycombs. The center (core) of these disks is less dense and hotter (up to 18°C). This is where honeybees produce most of their heat by eating and processing the sugars in honey.

Because bees’ body temperature is very low, the cooler outer layers (mantle) produce very little heat. If the temperature drops below 10°C, the bees there will die. Texts and scientific articles on beekeeping since 1914 say that the mantle “insulates” the inner core of the hive. This meant that beekeepers viewed clustering as natural and even necessary.

This belief was used in the 1930s to justify keeping honeybees in thin-walled hives, even in -30°C climates. This led to the practice in Canada in the late 1960s of keeping honeybees in cold storage (4°C) to keep them in colonies during the winter months. In the 2020s, keepers refrigerate bees during the summer months to make it easier to chemically treat parasites. This is happening in the USA; for example, in Idaho, Washington, and Southern California.

Outside of cold winter, beekeepers often need to find the queen and place her in a cage if they want to treat a mite infestation. But cold storage means beekeepers can skip this time-consuming step, making commercial pollination services more profitable.

warm-up challenge

However, research has shown that cluster shells act more like heat sinks, reducing insulation. Bundling isn’t about wrapping yourself in a thick blanket to stay warm, it’s more like a desperate struggle to get closer to the “fire” or die. The only benefit is that the mantle helps keep nearby bees alive.

When the temperature outside the hive drops, the bees around the mantle enter hypothermic hibernation and stop producing heat. The mantle contracts when bees try to keep the temperature above 10°C. The convergence of the bee cover increases the thermal conductivity between them and reduces insulation.

Heat will always try to move from a warmer area to a colder area. The rate of heat flow from the nuclei bees to the mantle bees is increased by keeping these bees at (hopefully) 10 °C on the outside of the mantle.

Consider a down jacket; It is the air space between the feathers that helps keep the wearer warm. A honeybee cluster is like compressing a down jacket so that the thermal conductivity eventually increases to that of a dense layer.

In contrast, when penguins gather together during the Antarctic 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 confinement.

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

The thin wooden walls of industrial beehives are only the boundary between the air space and the outside world. This means that the hive walls must be largely insulating, such as 30mm polystyrene, to be effective.

This misunderstanding of the complex interplay between the colony envelope, thermofluids (heat, radiation, water vapor, air), and honeybee behavior and physiology is the result of people not recognizing the hive as an extended phenotype of the honeybee.

Other examples of the extended phenotype include spider web and beaver comb.

There are almost no ethical standards regarding insects. But there is growing evidence that insects feel pain. A 2022 study found that bumblebees respond to potentially harmful stimuli similarly to pain responses in humans. There is an urgent need to change beekeeping practices to reduce the frequency and duration of clustering.