University of Tennessee professors collaborate to study magnetism of bees

As married research professors at the University of Tennessee, Knoxville, Dustin Gilbert and Anne Murray often discuss their work once they get home each night. Their fields of study rarely crossover. That changed six years ago, however, and it was insects that sparked the intersection. 

Murray, a research assistant professor in ecology and evolutionary biology in the College of Arts and Sciences, asked Gilbert, “Did you know honeybees are magnetic and cansense the geomagnetic field?” 

Gilbert, an associate professor in the Department of Materials Science and Engineering, had no idea. But his curiosity was piqued. Gilbert’s research focuses on functional materials and nanotechnology, with an emphasis on magnetism. Together, they formulated a plan to combine their knowledge and launch a novel project on bee magnetism. 

There are more than 20,000 different bee species in the world. If honeybees were magnetic, Gilbert and Murray wondered about other bees. After reviewing the literature, they learned that the magnetism of honeybees was discovered in 1977. Since that time, only four other bee species had been identified as being able to sense magnetic fields. 

Gilbert, Murray, and Laura Russo, an assistant professor in ecology and evolutionary biology at UT who performs research on native bee species, set out to provide a more definitive cataloging of bee magnetism. Over the last six years, they have tested more than 120 different species of bees and found that nearly 90 percent are magnetic. Their research was published this month in Science Advances. 

“It just was so unexpected. There had been some work on it, but we decided to cast a wider net out of curiosity and wonder,” said Murray, whose research focuses on insect sensory behavior, such as how chemicals released by plants mediate key ecological relationships with insects and fungi. “What has been the most surprising thing is there are so many and so much variety. We just weren’t expecting that.” 

Interpretive bee dancing 

Magnetoreception is the innate capacity of many animals to sense and use the Earth’s magnetic field. It is often used for navigation, much like how humans use a compass or a map. While many animals use this for long-range migration, the honeybee uses it to communicate directions to foraging sites to other bees. 

Female honeybees go out to collect pollen, bring it back to the hive, and then share the location with their peers. The honeybees communicate with each other by doing an interpretive dance so their peers know where the pollen can be found. The original 1977 observation was that if a magnet was placed near the honeybee’s nest, the bee would change direction of her dance depending on the placement of the magnet. However, recent experiments have cast doubt on this theory, making the actual use of magnetism more mysterious. 

“The idea was that the bee aligns its dance with the magnetic field, and then does its dance, and then everybody watching it can leave and use their magnetic sense to guide them to find the flowers,” Gilbert said. “It’s kind of like giving a pointer. That’s why they said these bees are magnetoreceptive. But none of the other four species of bees that had been studied before we started our research have a dance, so what do they use it for?” 

That’s the answer the UT research group has been hoping to discover. 

To study the bees, the group collected species from across the world. Previous papers inferred a connection between magnetoreception and social behavior because of the honeybee’s dance—although no one followed up by testing for magnetism in solitary bees. The UT team expanded the plan; from mapping how prevalent bee magnetism is to seeking correlations with the bee’s natural history and behavior. 

Russo provided her expertise on bee diversity and social behavior, and contributed bees from her own extensive collection to test. To fill out their sampling, the team requested bee species from other collections, including York University in Canada and The Smithsonian. The priceless collections were delivered in everything from leather-bound cases to generic pizza boxes. 

“We first sampled social and solitary members of the bee family Apidae, which included all previous species that had been reported ferromagnetic,” Russo said. “We originally thought only the social species would be magnetic, but ferromagnetism was well-represented in the solitary species as well. Then, we had to broaden the scope of our hypotheses.” 

Moving up the evolutionary tree 

In their research, Russo, Gilbert, and Murray found the strength of the magnetic signal wasn’t the same for every bee. Biggers bees and bees that are more social tended to have a stronger magnetic signal. 

The research group began exploring whether natural history, including a bee’s sex, sociality, habitat, geography, and nesting habits, explained the presence of ferromagnetism. Russo performed extensive statistical analysis, and Gilbert studied every component of magnetism. They couldn’t find one explanatory factor.  

That led them to move up the evolutionary tree and begin testing wasps to see if the magnetism existed in ancestral insects even before bees evolved. Along with new insects, came new collaborators, with bees and wasps being shipped from the University of Alaska, University of Hawaii, Australian National University, the University of Oldenburg in Germany, and the University of São Paulo in Brazil among other places. 

In testing nearly 300 species of wasps, they found that 90 percent are magnetic. 

“Altogether, this suggests that magnetoreception is a sense that goes back further in the evolutionary tree and continues to provide an unknown advantage,” Gilbert said. “While the prevailing theory is that insects use vision to navigate, our data suggests that magnetism may also play a crucial role, probably in short-range navigation. But we still don’t know for sure why they use magnetic fields and why it seems to have persisted for 150 million years.” 

Gilbert and Murray plan to continue the project to try and find the answer. They never imagined Murray’s question about honeybees would lead to a passion project that isolder than their 5-year-old son. But both are thrilled to be using their individual research strengths to work together. 

“The interdisciplinary nature of this project makes it very fun and interesting,” Murray said. “There are very different approaches to doing things and very different assumptions. It really expands your view. It’s been enjoyable, and it’s been very cool to bring these different areas together.”