When bees approach an object, according to previous work, they steadily slow down to a stop by adjusting their speed as the size of their target steadily looks larger. Srinivasan wanted to know what happens after that.
Along with colleagues, he set up a platform that could be adjusted to any angle from horizontal to vertical and even upside-down.
Using sugar water, the scientists trained honeybees to fly to the platform again and again. Then, the researchers turned on the high-speed camera.
Their footage showed that no matter how flat or steep the surface, bees slow to a hover at 13 millimeters (about half an inch) away from wherever they're going to land. That suggests, Srinivasan said, that the insects are somehow using their eyes to measure that specific distance.
"We don't know how they're doing it," he said, "But they're doing it."
If their landing surface was flat, the researchers report today in the Journal of Experimental Biology that bees simply touched down back legs first.
If the platform was anywhere between vertical and upside-down, on the other hand, the insects made contact with their antennae first, by pointing them almost perpendicular to the platform. Then, the bees hauled their front legs up and finished with a flip-like maneuver to get their mid-legs and rear legs onto the surface.