The total solar eclipse of 21 August 2017 traversed 5,000 km from coast to coast of North America. In its 90-min span, sunlight dropped by three orders of magnitude and temperature by 10-15 degrees Celsius. To investigate impacts of these changes on bees, a team of professional and citizen scientists led by University of Missouri’s Professor Candace Galen monitored their flights acoustically in natural habitats of Pacific Coast, Rocky Mountain, and Midwest regions. The results were clear and consistent at locations across the country: bees stopped flying during the period of total solar eclipse.
“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,” Professor Galen said.
“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.”
Supported by a grant from the American Astronomical Society, the project engaged more than 400 participants in setting up 16 monitoring stations.
At each location, small USB microphones were hung on lanyards near bee-pollinated flowers in areas away from foot and vehicle traffic. In some of the locations, light and temperature data were also captured.
Participants then sent the devices to the team’s lab, where the recordings were matched up with the eclipse periods from each location and analyzed for the number and duration of bee flight buzzes.
The recordings didn’t allow for differentiation between bee species, but participant observations indicated most bees monitored were bumblebees or honeybees.
The data showed that the insects remained active during the partial-eclipse phases both before and after totality, but they essentially ceased flying during the period of totality.
However, shortly before and shortly after totality, bee flights tended to be longer in duration than at times early in the pre-totality phase and late in post-totality.
The study authors interpret these longer flight durations as an indicator of slower flight under reduced light or possibly as the bees returning to their nests.
Bees commonly fly more slowly at dusk and return to their colonies at night, and so the same behavior triggered by a solar eclipse offers evidence about how they respond to environmental cues when those cues occur unexpectedly.
“The eclipse gave us an opportunity to ask whether the novel environmental context — mid-day, open skies — would alter the bees’ behavioral response to dim light and darkness. As we found, complete darkness elicits the same behavior in bees, regardless of timing or context. And that’s new information about bee cognition,” Professor Galen said.
This research was presented in a paper published in the Annals of the Entomological Society of America on October 10, 2018.
Candace Galen et al. Pollination on the Dark Side: Acoustic Monitoring Reveals Impacts of a Total Solar Eclipse on Flight Behavior and Activity Schedule of Foraging Bees. Annals of the Entomological Society of America, published online October 10, 2018; doi: 10.1093/aesa/say035