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From left, Francisco��López Jiménez, Orit Peleg and graduate student Richard Terrile inspect the honeycomb in a bee hive. (Credit: Patrick Campbell)
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On a hot summer day in Colorado, European honeybees (Apis mellifera��L.) buzz around a cluster of hives near Boulder Creek. Worker bees taking off in search of water, nectar and pollen mingle with bees that have just returned from the field. Inside the hives, walls of hexagons are beginning to take shape as the bees build their nests.

“Building a hive is a beautiful example of honeybees solving a problem collectively,” said Orit Peleg, associate professor in ��ƷSM����ӰƬ’s Department of Computer Science. “Each bee has a little bit of wax, and each bee knows where to deposit it, but we know very little about how they make these decisions.”

In an in PLOS Biology, Peleg’s research group collaborated with Francisco López Jiménez, associate professor in CU’s Ann and H.J. Smead Department of Aerospace Engineering Sciences, and his group to offer new insight into how bees work their hive-making magic—even in the most challenging of building sites.

The new findings could spark ideas for new bio-inspired structures or even new ways to approach 3D printing.

How and why bees build honeycomb

Honeybees can build nests in any number of places, whether it’s a manmade box, a hole in a tree trunk or an empty space inside someone’s attic. When a bee colony finds somewhere new to call home, the bees build their hive out of honeycomb—a waxy structure filled with hexagonal cells—on whatever surfaces are around.

Building a beehive is hard work, and it consumes a lot of resources. It all starts with honey, the nutrient-dense superfood that helps bee colonies survive the winter.

To make honey, bees spend the warmest months gathering nectar from flowers. The nectar mixes with enzymes in the bees’ saliva, and the bees store it in honeycomb cells until it dries and thickens.

It takes roughly 2 million visits to flowers for bees to gather enough nectar to make a pound of honey. Then, each worker bee must eat about 8 ounces of honey to produce a single ounce of the wax they need to build more honeycomb.

If the surface of their building site is irregular, the bees have to expend even more resources building it, and the resulting comb can be harder to use. So efficiency is key.

In an ideal world, bees try to build honeycomb with nearly perfect hexagonal cells that they use for storing food and raising young larvae into adults. Mathematically, the hexagonal shape is ideal for using as little wax as possible to create as much storage space as possible in each cell.

The honeycomb cells are usually a consistent size, but when bees are forced to build comb on odd surfaces, they start making irregular cells that take more wax to build and aren’t as optimal for storage or brood rearing.

Irregular surfaces: A puzzle for bees to solve

This hive frame shows a foundation with a smaller cell size than what bees would typically build. The bees adjusted their building strategies to adapt. (Credit: Patrick Campbell)

Golnar Gharooni Fard, the lead author of the new study and a former CU graduate student, said her main goal in the study was to understand how bees work together to solve the structural problems they might run into.

“We wanted to find the rules of decision-making in a distributed colony,” Fard said.

The researchers 3D printed panels, or foundations, for bees to build comb on. The team imprinted the foundations with shallow hexagonal patterns with differing cell sizes—some larger, some smaller, and some closer to an average cell size—and added the foundations to hives for the bees to use.

Next, the researchers used X-ray microscopy to analyze patterns in the comb the bees built on each type of foundation. Depending on which foundation they were given, the bees used strategies like merging cells together, tilting the cells at an angle or layering them on top of one another to build usable honeycomb.

Giving bees these different surfaces to work with was like giving them puzzles they had to solve, said López Jiménez.

“All those things happen in nature. If they're building honeycomb on a tree, and at some point they get to the end of the branch, the branch might not be super flat, and they need to figure that out,” he said.

It’s still not clear why bees use the strategies they use in all situations. That’s a question the researchers hope to continue exploring.

Meanwhile, the team sees numerous possible applications for their findings. For example, honeycomb could inspire designs for efficient, lightweight structures such as those used in aerospace engineering.

López Jiménez also likened the honeycomb building process to 3D printing, where each bee gradually adds tiny bits of wax to the larger structure.

“The bees take turns, and they organize themselves, and we don't know how that happens,” he said. “Can we learn from how the bees organize labor or how they distribute themselves?”

CU graduate student Chethan Kavaraganahalli Prasanna was also part of the research team.