Insects and other flying animals are somehow able to maintain appropriate flying heights and execute controlled takeoffs and landings despite lacking the advantage of sophisticated instrumentation available to human aviators. By characterizing the behavior of a specially designed flying robot, researchers have now been able to test a theory that helps explain how visual cues are used by insects during flight to ensure appropriate distance from the ground. The work, reported by Nicolas Franceschini and colleagues at France's CNRS and the University of the Mediterranean in Marseille, will appear in Current Biology online on February 8th.

When insects fly, the image of the ground beneath them sweeps backward across their visual field in a way that depends both on the insect's height above the ground and on its speed relative to the ground--essentially, the higher the insect, the slower the ground will appear to move below it. This visual sweep, known as "optic flow," therefore potentially provides crucial information to the insect about its position relative to the ground, but it remains unclear exactly how such information is translated in a way that helps keep insects from crashing during flight.

In their new work, the authors hypothesized that insects rely on a visual feedback loop, termed an optic-flow regulator, to assess the ratio of groundspeed to height, and to maintain that ratio by controlling their vertical lift. To test this hypothesis, the researchers engineered a fly-by-sight micro-helicopter that incorporated control elements based on the idea of an optic-flow regulator, and found that the robot was indeed capable of achieving impressive aspects of insect flight, including takeoff, level flight, and landing.

The findings, explain the authors in their paper, help illuminate the basis for a number of previously unexplained observations regarding insect flight, including the fact that many insects descend in a headwind and ascend in a tailwind, and that honeybees often drown when flying over mirror-still water.

The researchers include Nicolas Franceschini, Franck Ruffier, and Julien Serres of Centre National de la Recherche Scientifique and University of the Mediterranean in Marseille, France.

This research was supported by the Centre National de la Recherche Scientifique (Life Science and Engineering Science) and the European Union (contract IST/FET199929043).

Franceschini et al.: "A Bio-Inspired Flying Robot Sheds Light on Insect Piloting Abilities" Publishing in Current Biology 17, February 20, 2007.

Note: This article has been adapted from a news release issued by Cell Press.