Bees Go Silent During a Total Solar Eclipse

As the moon blocked the sun across a swath of North America last year, millions of people got to see a total solar eclipse for the first time in their lives. So did countless nonhuman animals — albeit without the benefit of knowing what was happening.

Many animals are confused by total solar eclipses, although the phenomenon occurs so sporadically — and so often over oceans — that there isn't a lot of research on how various species react to it. That includes bees, important pollinators known for staying busy throughout the day as long as there's sunlight. Since the Great American Eclipse's path of totality crossed such a large area of land, it provided a rare opportunity for scientists to study its effects on these industrious insects.

And that's what a team of researchers did on Aug. 21, 2017, enlisting help from citizen scientists and elementary-school classrooms to gather data during the eclipse. Their findings, published this week in the Annals of the Entomological Society of America, were "clear and consistent at locations across the country," the researchers report. Instead of gradually quieting down as expected, bees seemed to mostly ignore the eclipse until the moment of totality — then suddenly went quiet.

"We anticipated, based on the smattering of reports in the literature, that bee activity would drop as light dimmed during the eclipse and would reach a minimum at totality," says lead author Candace Galen, a professor of biology at the University of Missouri, in a statement. "But we had not expected that the change would be so abrupt, that bees would continue flying up until totality and only then stop, completely. It was like 'lights out' at summer camp! That surprised us."

'Perfect fit'

Before this study, Galen and her colleagues had recently field-tested a new system that remotely tracks bee pollination with "soundscape recordings" of their buzzing noises. And since there's so little formal research on insect behavior during eclipses, especially among bees, they realized this system could help fill the void.

"It seemed like the perfect fit," Galen says. "The tiny microphones and temperature sensors could be placed near flowers hours before the eclipse, leaving us free to put on our fancy glasses and enjoy the show."

Along with 10 other researchers from Missouri and Oregon, Galen received a grant from the American Astronomical Society to conduct this study during the eclipse. Their project featured more than 400 participants — including scientists, elementary school students and teachers, and various other members of the public — who helped set up 16 monitoring stations across the path of totality in Oregon, Idaho and Missouri. At each station, the participants hung small USB microphones — or "USBees" — near bee-pollinated flowers located away from foot and vehicle traffic.

After the eclipse, all the data were sent to Galen's lab, where the researchers matched the recordings with eclipse timing for each location, then analyzed the number and duration of buzzing sounds created by flying bees. They couldn't identify bee species based on buzzing alone, although they note participants' observations suggest most of the sounds came from either bumblebees or honeybees.

Buzzing off

The data revealed that bees continued buzzing during the partial-eclipse phase before totality, then went almost completely silent when the moon fully obscured the sun. (Just one buzz was recorded during totality across all 16 stations, they report.) As totality ended and sunlight began to reappear, the bees began buzzing again.

That sudden silence was the biggest change, but there were also subtler differences. Just before and after totality, bee flights tended to last longer than they had earlier in pre-totality and later in post-totality. It's unclear why, but Galen and her colleagues suspect the longer flight durations may represent slower flight speeds due to lower light levels, or maybe a signal that bees were returning to their nests.

"The way I think about it is, if you're driving on a road and it gets foggy, you slow down," Galen tells Smithsonian Magazine. Reduced visibility would be a sensible reason for bees to slow down, and previous research has reported bees doing just that at twilight. And although they're mostly anecdotal, some reports from past eclipses also described bees going home as the moon eclipsed the sun.

During a total solar eclipse in June 2001, for example, astronomer Paul Murdin observed how various wildlife reacted at Mana Pools National Park in Zimbabwe, including bees. Murdin watched the bees withdraw to their hive in the late stages of the eclipse, he wrote, then saw them try reconnaissance: "Two scout bees left the hive after the eclipse and returned later, but whatever they reported, the swarm of bees did not leave the hive again that afternoon."

Thanks to the power of citizen science, we now have the best data yet on how a total solar eclipse affects bees. That may seem trivial, but given the ecological and economic roles these pollinators play (and their struggles with habitat loss, pesticides and disease), almost any insight about bee behavior could be valuable. "The eclipse gave us an opportunity to ask whether the novel environmental context — midday, open skies — would alter the bees' behavioral response to dim light and darkness," Galen says. "As we found, complete darkness elicits the same behavior in bees, regardless of timing or context. And that's new information about bee cognition."

Bee students

Eclipse science is relatively rare, thanks to the spotty nature of eclipses, but we won't have to wait long for a followup to this study. The U.S. is entering a "new golden age of eclipses," as MNN's Michael D'Estries wrote last year, noting that while "the 20th century only had two total eclipses, in 1918 and 1970, over large amounts of the U.S., the 21st century will have no fewer than six prime total eclipses, with four of them occurring within a 35-year period."

In fact, another total solar eclipse will race across North America on April 8, 2024, and Galen says her team is already planning another bee study. The researchers are working to improve the audio-analysis software, she says, to distinguish the sounds made by foraging bees as they leave or return to their colonies.

And, as she and her colleagues write, they don't expect to have trouble recruiting more citizen scientists to help. Not only did the 2017 eclipse demonstrate Americans' enthusiasm for this kind of thing, but the project may have instilled a long-term interest in some of the elementary schoolers who participated.

"[A]t the end of the project, we asked students to create cartoons illustrating the eclipse from a bee's perspective, as a way to synthesize their results. These illustrations show growth in their understanding of animal behavior over the project — many drawings captured the connections between environmental stimuli, bee sensory systems and flight responses," the researchers write in their study.

"The next total solar eclipse will come through Missouri in 2024," they add. "We bee chasers, including some promising new recruits, will be ready."