Most bumblebees spend a good chunk of their lives foraging for enough food to feed the queen, flying heavy loads of either pollen or nectar to and from the hive. Usually, these loads are equal to or more than half their own body weight. Until recently, scientists have long wondered how carrying these heavy loads, so vital to the health of the hive, affects the way in which bumblebees fly. The answers to these questions, recently published in the Proceedings of the National Academy of Sciences online journal, indicate that bumblebees are picky, choosing which source of food to collect depending on the weather in order to maximize their flight efficiency.
An Old Hypothesis
When bees collect nectar, they stick it to their abdomens. When they collect pollen, they glue it to their legs in clusters. According to data collected from Harvard University and the Royal Melbourne Institute of Technology , the bumblebee chooses between collecting pollen or nectar based on how it will later affect their maneuverability and stability—all the while taking weather conditions into account. This has been consistently hypothesized by scientists throughout history, but only recently has been confirmed through thorough and complex experimentation.
The Experiment
Biologist Andrew Mountcastle from Harvard and aerospace engineer Sridhar Ravi, PhD performed experiments on bumblebees by attaching artificial weights to their bodies. On some, they attached the weights to their legs, in place of pollen, while others had weights glued to their torsos, to simulate loads of nectar. The bees were then placed in a wind tunnel, where the bumblebees in flight were subjected to a variety of different wind conditions, with a promise of juicy, nectar-filled flowers at the opposite end. Using a high-speed camera, researchers were able to carefully track the bumblebees’ flight patterns, revealing new information as to how what they carry affects their flight.
The Results
After analyzing the video, the team of researchers confirmed that what bumblebees choose to carry significantly affects the ways in which they fly. Bees that were observed carrying pollen on their legs proved to be much more stable in windy conditions than those carrying nectar on their torsos, as the weight distributed evenly among their legs provided them with a much more steady and consistent flight.
However, bees that carried nectar instead of pollen proved to have much more maneuverability. This tradeoff of stability for maneuverability was determined when researchers found that bees carrying pollen had a significantly harder time tracking moving targets than those carrying nectar.
If the flight paths of bees are so easily affected by what they carry, then is it possible that bumblebees take weather into account when deciding between carrying nectar and pollen back to the hive?
Researchers like Ravi and Mountcastle predict that they do, perhaps choosing to take advantage of pollen’s more stable loads on windier days, and carrying the easily-maneuvered nectar on calmer ones. Experiments are in the works as we speak to help scientists answer this question, which would help conservationists and researchers alike better understand how weather could potentially affect the overall health of bumblebees—the populations of which have been steadily declining for some time now.
