Honey bees secretly stockpile structures symmetrically

Symmetry is everywhere, and for many different reasons.  Humans find symmetrical faces more attractive, and symmetrical buildings, like the Taj Mahal, aesthetically pleasing.  Most animals also have symmetrical body plans, which helps them with balance and movement. For similar reasons, the cars, planes, and trains that humans build are symmetrical.

However, just because a body is symmetrical, does not mean that it’s symmetrical throughout.  The human heart, for example, is on one side of the body. Similarly, while a house might be symmetrical from the outside, the organization of rooms and furniture inside are not necessarily symmetrical. Therefore, while symmetry is extremely common, it often is only on the outside, not inside.

An international group of researchers, led by the Smith Bee Lab at Auburn University, have now shown that honey bees symmetrically organize the internal contents of their nest. This creates a mirror image, where the contents on one side of the honeycomb match the opposite side.  What’s more, this symmetry benefits the colony, and is found across all species of honey bees they investigated. 

The famous honeycomb that bees build, with all the individual hexagonal cells, is double-sided.  This had been known for as long as humans have interacted with honey bees, and the double-sided arrangement was thought to exist solely to reduce wax use (a precious resource for the bees).  

What the researchers showed was that if you compare the two sides of the comb, what the bees put into each cell is a mirror image on either side of the comb. In other words, if honey is located on one side of the comb, there will also be honey on the other side, and the same for pollen, brood, and empty cells.  This pattern exists throughout a colony’s life; whatever is on one side of the comb is a mirror image of the opposite side.

“We kept colonies in huge observation hives, so that the bees could build a full-sized nest between the two panes of glass, and we could inspect the nests many times without disturbing them. The only problem is that when you want to map the nest, all the bees are also in there, so you have to wait until they move out of the way to peek inside each cell. Fortunately, with a good headlamp and a dedicated research team, we were able to collect 148 nest maps from six colonies” said Michael L. Smith, PI of the Smith Bee Lab, and first-author of the study published in Current Biology.

The researchers then wanted to know if workers needed to be in direct contact with both sides of the comb to create this symmetrical pattern. To do this, they invented a special type of observation hive, where the base of the comb is impermeable, so independent colonies can build and stockpile nests on either side however they wish. To their surprise, the independent colonies mimicked each other’s nest organization, despite not being in contact with one another (each colony had its own nest entrance, and the workers do not mix between colonies).

The researchers then hypothesized that heat might be a way for colonies to indirectly communicate the position of different nest contents.  After all, honey bees are extremely particular about the temperature of their nest, because it’s critical for the development of the brood. The researchers placed heat pads set to broodnest temperature on one side of their special observation hives in random locations, and then installed a colony on the other side.  Ten days later, they came back to see where each colony built their nest, and found that 100% of the capped brood was perfectly aligned with the position of the heat pad. 

“When we mapped these colonies, we were blind to the position of the heat pad, because we didn’t want to accidentally bias ourselves. But the brood pattern was striking – you were practically tracing out a rectangle of brood on one side, which matched the heat pad on the opposite side.” said Claire Bailey, then an Auburn undergraduate in the Department of Biological Sciences and co-author of the study, now a PhD student in the Barden Lab at NJIT.

“While there are many models for how honey bees might organize their nests, this experiment provides empirical evidence that temperature cues are an important factor” said Smith. 

Other types of symmetry provide tangible benefits, such as improved locomotion for a symmetrical organism. To test how nest symmetry benefits a colony, if at all, the researchers created one-sided and two-sided nests (colonies living in two-sided nests made their nest symmetrical, but colonies living in one-sided nests could not). There were clear benefits of a symmetrical nest – after only ten days, symmetrical nests had almost 60% more brood than their non-symmetrical counterparts. Furthermore, the temperature profile of the symmetrical nests was more stable, which is critical for the developing brood.  

Finally, the researchers wanted to see if these results were just an oddity of keeping bees in observation hives, and whether they would find similar symmetry in other species of honey bees (genus Apis). 

To answer whether this pattern would also exist in multiple-comb nests, like honey bees build in the wild, the researchers took images of “natural comb” from 3-dimensional nests, where the bees were free to build their combs from scratch (i.e., no artificial comb templates provided, like beekeepers would typically use).  This, however, created a problem, as the colonies generated a massive amount of data. Through a collaboration with Dr. Ben Koger, Assistant Professor at the University of Wyoming, they were able to develop an automated method for classifying per-cell contents from an image. “This is a great example of how biological questions can be merged with new techniques from computer science. While technically you could do this by hand, it would take so much time, that it’s just not practical” said Koger. Comparing the two sides of comb, yet again, they found that the bees stockpiled each comb symmetrically. “The combs are not interchangeable across colonies, or even within the same colony. Each one is symmetrical, creating a type of internal symmetry within their nest architecture” said Smith.

“Students in the lab kept saying that we had to finish up the project, but as a long-shot, I wanted to see if we could also find the same type of symmetry in other species of Apis. Fortunately, we have a great collaborator in Thailand” noted Smith. Dr. Bajaree Chuttong, from Chiang Mai University in Thailand, happened to have just what they needed – images of both sides of natural nests, from multiple honey bee species (Apis andreniformis, Apis dorsata, and Apis florea). When they compared both sides of each nest, they found that all these species also stockpiled their nests symmetrically. 

This told the researchers that this architectural symmetry was not limited to the Western honey bee.  All species of honey bees build double-sided comb, and all of them organize their nest contents symmetrically on either side of the comb. Presumably, during the earliest evolution of Apis nest architecture, workers build double-sided comb to conserve wax, but this also provided a thermoregulatory benefit for rearing brood, and shows a novel benefit of creating symmetry, this time in the internal nest architecture of the honey bee.

Citation:

Smith et al., Form, function, and evolutionary origins of architectural symmetry in honey bee nests, Current Biology (2024), https://doi.org/10.1016/j.cub2024.10.022

Funding:

This work was funded by the National Science Foundation (grant number 2216835), the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany’s Excellence Strategy – EXC 2117 – 422037984, a CASCB Project Proposal, the Alabama Agricultural Experiment Station, and the USDA Hatch Act program. Funders had no role in study design, data collection and interpretation, or decision to publish.