Honeybees are known to be talented aviators, but according to an experiment that was carried out in 1963, they have difficulties when they must fly over a mirror-like surface, like a smooth lake.

That was the year when an experiment was carried out by German behavioral scientist Martin Lindauer and Austrian entomologist Herbert Heran.

Their experiment revealed that the bees were only able to fly across a lake if the water was turbulent or rippling. If the surface was glassy smooth like a mirror, the bees started to lose altitude and eventually crashed into the liquid-like glass surface. At that time, nearly 60 years ago, the findings reflected that bees needed visual cues while navigating in flight.

A new study adds fascinating insights. The 1963 experiment was closely replicated, and researchers note that watching as the ground speeds by below helps honeybees to regulate their in-flight altitude. Experiments were inside a 220-centimenter (87-inch) long outdoor tunnel, with a mirrored ceiling and floor that could be covered to look like walls.

The honeybees usually flew from one side of the tunnel to the other at quite a constant altitude when all the mirrors were covered, to collect a sweet treat. If the ceiling was pulled back and a mirror was revealed, it seemed the height of the tunnel doubled, and the bees made it across without incident.

When the floor became a mirror, the ground looked twice as far away. The bees began to crash. They started off by flying normally, but about 40 centimeters (15 inches) in, their altitude began to drop until the insects hit the glass floor.

When both ceiling and floor were mirrored, making a parallel pair of infinite walls, the bees started to lose altitude after flying only around eight centimeters (three inches), and hit the ground sooner.

This unrelated 1:46-minute video by Institut des sciences du movement shows the experiment mentioned in this post:



These findings are similar to the spatial disorientation that human aviators suffer from at times. When pilots cannot see their ground speed, they are challenged to maintain altitude. Airplane instruments help pilots to overcome spatial illusions to keep aircraft aloft even if there is no texture or shadow on the ground or water below.

Honeybees do not have such a backup system to help them. Even if a mirrored floor only existed in the second half of the tunnel, their steady flight from the first half suddenly experienced an abrupt plunge.

The double mirror condition allowed scientists to get closer to the flight conditions of an open sky flight over a calm water surface, according to the authors of this new research. New findings agree with the results of Lindauer and Heran in that, honeybees lose altitude in the absence of ventral optic flow.

It seems bees use visual cues they see on the ground to maintain altitude, as opposed to visual cues from the sky above. If the ground stops giving a proper baseline, researchers think the insects drop lower in altitude to see if they can regain that 'ventral optic flow'. They think it is farther away than it is, so they crash to the ground.

If the bees in the experiment were given a wider visual field, they may have used other cues to help maintain altitude. But flying across a large, glassy lake or a closed-in tunnel offers few alternatives the insects can use to gauge altitude.

A similar experiment found fruit flies do not use ventral optic flow to control their altitude. Different species appear to use different techniques to maintain flight.

The study was published in Biology Letters.