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Honeybees move quickly from flower to flower, landing easily on each one in turn 鈥� but a study involving small drones suggests that the undertaking is more difficult than it looks, implying the bees rely on learning as well as hardwired instinct.

Bees and other insects judge movement using what is called 鈥�optical flow鈥� 鈥� basically the rate at which things are moving through the field of view.

Optical flow is useful during landing too, particularly to help a bee decelerate. This is because the nearer an object is, the faster it moves through the field of vision, which means that if a bee maintains optical flow at a constant apparent speed as it approaches an object, it automatically slows down for a soft landing.

For added information, bees in the process of landing also rely on an aspect of optical flow called 鈥渄ivergence鈥�, which is the rate at which objects in the field of view are getting bigger.

Researchers in the Netherlands and Germany tried to program this insect guidance system into their small drones. But they couldn鈥檛 get the technique to work, because at very low speeds, optical flow didn鈥檛 distinguish speed and distance well enough.

鈥淥ur flying robots would not actually land, but they started to oscillate, continuously going up and down, just above the landing surface,鈥� says Guido de Croon at the Delft University of Technology in the Netherlands.

De Croon鈥檚 team solved the problem by having the drone learn what surfaces such as bark or grass looked like at different distances. This gave the drone additional information to supplement what it could gain from tracking the size and movement of objects.

Now the oscillations, which had been a problem, proved helpful: they allowed the drone to learn how surface texture appeared at different ranges. The approach of optical flow plus learning proved far more successful.

鈥淚t leads to really fast and smooth landings,鈥� says de Croon.

We don鈥檛 know for sure whether bees have evolved a similar solution. However, Tobias Seidl, a biologist at the Westphalian University of Applied Sciences, Germany, and a co-author on the study, notes that honeybees in a new environment do appear to go through a learning phase. During this, they may oscillate up and down before landings, similar to the drone.