Without street signs or GPS, animals develop specific and effective strategies for getting where they need to go. To efficiently navigate, honeybees fly lower when facing into the wind and higher when flying with the wind. To understand how some bees determine flight routes despite varying wind conditions, Emily Baird and colleagues at the Australian National University measured whether honeybees’ sight governs their flight paths. They found that bees control their speed and distance from the ground by using different elements of their vision, and that the insects stay on track by making small swerves to the left and right in a wavy pattern.
To measure the insects’ flight routes, the team tracked their height and speed relative to the ground by analyzing videos of bees flying through a small wind tunnel, which enabled them to control the speed of the airstream the bees encountered (still air, slow 1 m s−1 or fast 2 m s−1), as well as the direction, so that the bees were flying into the wind or with it. To maximize the visual information available to the bees, the walls of the wind tunnel were lined with a pattern of intersecting perpendicular and parallel stripes made out of red tape on white paper. As the bees flew past the stripes, they swerved left and right, creating a wavy route that allowed the team to better see how they moved in relation to the stripes. Regardless of wind direction, they flew at similar speeds of 0.5 m s−1 but flew lower against the wind and higher when flying with the wind. By measuring what the bees could see based on where they were in the wind tunnel, the researchers determined that the bees maintained a constant view to each side regardless of wind direction, but their view of the ground changed at different heights, which would allow them to achieve different heights in different wind directions.
To test whether the bees were relying on the parallel or the perpendicular stripes to determine how high to fly, they used only one stripe orientation, or no stripes at all. When the bees’ visual information was limited by only seeing perpendicular stripes, they maintained similar speeds and swerves to those with full vision but were no longer consistent in their ground height. In contrast, when they could only see stripes parallel to their path, they again flew lower against the wind and higher when flying with the wind. Without seeing perpendicular stripes, though, the bees sped through the wind tunnel at about 1.5 m s−1 without swerving. To simulate low visibility conditions, the researchers tracked bees as they flew through the wind tunnel without any stripes at all – as though flying through dense fog. As with parallel stripes alone, the bees flew straight without swerving. However, without visual cues, their height was inconsistent and they instead modulated their speed to fly slower against the wind and faster with the wind.
Honeybees determine how high and how fast to fly according to what they see, and they judge what they see by weaving wavy flight paths in such a way that their own motion helps them to extract clues about their environment. Outside the wind tunnel, bees need to discover new paths based on ever-changing wind and visibility conditions. Instead of street signs, honeybees skilfully find routes using multiple strategies to determine where they are based on what they see.