Bees of many species contain tiny magnetic particles – suggesting they may have an innate magnetic compass for navigation
A surprisingly large number and diversity of bee species – 74 out of 96 tested – have magnetic properties, according to research my colleagues and I recently published in the journal Science Advances.
Some animals are able to use iron-based magnetic compounds such as magnetite to detect and navigate via the Earth’s magnetic field – a sense called magnetoreception. We considered magnetism in the insects we tested to be a proxy for which species might be magnetoreceptive.
For decades, biologists have known that social, cavity-nesting honeybees exhibit magnetoreception. Most researchers assumed that this internal compass was tied to living in a colony; honeybees communicate the location of floral resources to other colony members through a dance that indicates direction relative to the position of the Sun and the geomagnetic field.
Our study had two goals: to compare magnetism between bee species that live in groups versus on their own, and to track down the evolutionary origin of magnetoreception in bees.
Finding magnetism wherever we looked
To test magnetic responses, we collected bee specimens from across the bee family Apidae, which includes social species such as honeybees along with solitary species such as chimney bees. We ground dried dead bees into a powder, then measured how magnetic this powder was in a magnetometer.
To our surprise, we found that the magnetic response was strong in both bees that live in groups and those that live alone. This result forced us to reject our initial hypothesis that magnetism was necessary only for social bee species.
Even more unexpected, a bee from a small social species in the family Halictidae was also strongly magnetic. We then broadened our search to include bees from across the bee evolutionary tree, suspecting that the evolutionary origin of magnetism could be found in older bee lineages.
We identified some trends regarding the strength of the magnetic response of the bees in our study. Larger bees tested as more magnetic. Social bees did tend to be more magnetic than solitary bees. And cavity-nesting bees tended to be more magnetic than ground-nesting bees.
Overall, though, we detected magnetism across all the different families of bees, for social and solitary bees, in nocturnal bees, and in bees that live in nests in the ground as well as those that live above ground in hives. Insects from other groups we examined for comparison, including beetles, wasps and flies, were also magnetic.
We again had to reject our hypothesis; this time, we demonstrated that magnetism probably predates the evolutionary origin of bees. We concluded that magnetism is probably an ancient, well-conserved trait.
What still isn’t known
Our work leaves a lot of unanswered questions.
For one, although we assume that the magnetic response is a proxy for magnetoreception, it is notoriously difficult to demonstrate this because it requires experiments with live organisms removed from their natural environment.
Magnetoreception is one of the most controversial animal senses. While there is good evidence that some organisms have the ability to detect and navigate along the magnetic fields of the Earth, it is probably not the primary sense used, even for organisms that do have magnetoreception. That makes it a challenging sense to isolate and study. Even in bumblebees, which biologists believe are magnetoreceptive, there remain many questions and doubts about their use of this sense.
Scientists are more certain that honeybees are magnetoreceptive – researchers have even trained them to discriminate between local magnetic anomalies. So we made the assumption that insects we tested that had stronger magnetic responses than honeybees are also magnetoreceptive. But we cannot prove it. Moreover, our work does not explain the function of magnetism, nor the mechanism behind magnetoreception.
And while the strength of the magnetic signal varied among body parts, it was never restricted to a single body part in the bees we tested. This means that some of the hypotheses for how magnetoreception operates – for instance, through light-sensitive cryptochromes in the eyes – are not well supported by our results.
Laura Russo, Assistant Professor of Ecology and Evolutionary Biology, University of Tennessee
This article is republished from The Conversation under a Creative Commons license. Read the original article.
For centuries, scientists have explored and documented the natural world, collecting the billions of specimens housed in museums, universities, and field stations worldwide. And now, the University of Tennessee and other institutions across the globe want to help make that information available to the general public. 
“Natural history collections are a physical record of our planet’s biodiversity across space and time,” said Budke, who is also an assistant professor in the UT Department of Ecology and Evolutionary Biology. “These specimens not only serve as records of the past, but they are a critical resource for our future. They help us to answer important questions surrounding invasive species, conservation biology, and help us to describe species that are new to science.”
The WeDigBio Event emerged within the museum community to accelerate the rate of digital data creation about the historical what, when, and where of the perhaps 9 million species on Earth. It has a core leadership team that includes researchers from the Smithsonian Institution, the Australian Museum, Florida State University, University of Florida, and the major online transcription platforms, including the U.S.-based Smithsonian Transcription Center, Notes from Nature, and Symbiota, the Australia-based DigiVol, the UK-based Herbaria@Home, and the France-based Les Herbonautes.
This one-of-a-kind event will be held from October 14-17 at locations across the globe. Members of the public can contribute at any time from anywhere during the event at one of the participating online transcription platforms.
Being a 25+ year employee at UT has allowed me to experience several academic units. In all of the departments, it has been a pleasure to work with students and faculty from different regions of the world. The EEB department, however, has been a constant advocate for adding and bringing more diversity to the department, which has resulted in recruitment of some very intelligent (and active) faculty and students. Overall, a great department to be a part of!”
“Having worked in higher education for most of my career, I knew that UT has a wonderful reputation for research and education and employees rank the university as one of the best places to work in the state. It is the place I wanted to ‘hang my hat.’ 
“I had worked at the university for 22 years, but never in an academic department before given the opportunity to work in the Department of Ecology and Evolutionary. I knew this would push me mentally and to continue to learn the other side of how the university functions.
“Getting a job at the university was something I very much wanted to do. I was fortunate enough that my wealth of experience allowed me the opportunity to obtain a job at UT in the EEB department. I think it is wonderful seeing such a diverse group of people working in our office and in our department. I have been made to feel very welcome here at UT, which is one of the many reasons I chose to work for UT and EEB specifically.