Photomontage of a bumblebee approaching the hive, viewed from the top. Images taken at ∼0.1 s intervals.
Photomontage of a bumblebee approaching the hive, viewed from the top. Images taken at ∼0.1 s intervals.
As storms swept across northern Europe in February 2022, the UK public was captivated by YouTube videos showing colossal jets lurching in to land in powerful gusts of wind at Heathrow Airport. Each landing was fraught with danger. Yet bumblebees have to deal with buffeting crosswinds all the time, and their aeronautic escapades never make the headlines. Keeping track of their landing site as they approach in still air, bumblebees periodically adjust their speed as the landing site looms toward them, slowing before setting down. But no one knew how the insects fine-tune their approach when swept sideways in a breeze. Would the bees depend solely on their vision to guide a successful landing, or would they require additional knowledge about the air rushing past their bodies to set down safely? Pulkit Goyal, Johan van Leeuwen and Florian Muijres from Wageningen University and Research, The Netherlands, set about filming bumblebees as they came in to land in a crosswind to discover how the insects execute their landings.
Goyal placed a hive of bumblebees on one side of a wind tunnel and provided the insects with a tempting sugar-water treat on the other side, so that the bees had to commute back and forth across the wind tunnel in still air. Once the bees had got the hang of going to and fro, or simply bumbling about, Goyal turned on the wind, at speeds ranging from 0.3 to 3.4 m s−1 (∼12 km h−1) – creating a crosswind that the bees had to overcome as they landed at the feeder and when returning home – while filming the bees’ manoeuvres in 3D. After recording more than 19,000 landings, Goyal then began the painstaking task of unravelling the bees’ strategies.
The team broke the flights down into landing approaches made directly after a take-off – either from the hive or the feeding station – or after a tour of the wind tunnel, and then focused on the final 0.4 m of the approach, and discovered that bees prefer not to land in a crosswind, reducing their landing rate by 60% after buzzing around the wind tunnel and 70% if they had just taken off. And when the team scrutinised the bees’ inbound trajectory, they were clearly flying hard to remain on course, drifting a little, especially in the strongest crosswinds.
In addition, the bees were gauging their approach guided by the speed at which their landing site appeared to loom toward them in their vision, just as they did in still air. However, despite landing less in high crosswinds, the bees that had toured around the wind tunnel prior to touchdown landed as fast as the bees in still air. The team also noticed that the buffeted bees broke their approach, hovering more often in the highest crosswinds. However, the interruptions did not slow their inbound trajectory. After pausing to hover and reset their view, the bees’ resumed approach was faster than in still air, allowing them to complete the final approach in the same time. And when the team compared the bees’ crosswind strategy with that of bees landing in a headwind, they realised that in addition to depending on their vision for a safe landing, the bees also relied on the feel of the air tugging on their antennae and bodies to guide their approach.
Although the option of stopping for a hover isn't viable for Heathrow's incoming jets, Goyal and colleagues suggest that engineers could learn from crosswind-defying bees when building flying robot automatic landing systems to guide them down safely when blown off course.
