Washington, Jan 18 (IANS) How do insects such as butterflies, locusts and fruit flies navigate thousands of miles so precisely with only the unchanging sky in the foreground? Researchers now have an answer.

“If you go out in a field, lie on your back and look up at the sky, that’s pretty much what an insect sees,” said study co-author Michael Dickinson, a University of Washington biology professor.

Peter Weir, doctoral student at the California Institute of Technology (Caltech), and Dickinson examined the behaviour of the fruit fly, in outdoor lighting conditions, to find answers, the journal Current Biology reports.

They demonstrated that fruit flies, equipped with complex compound eyes, keep their bearings by using the polarisation pattern of natural skylight, some of them for thousands of miles, according to Caltech-Washington statement.

Demonstrating that fruit flies can navigate using cues from natural skylight makes it easier to use genetics to better understand the complex capability and exactly how it is implemented in the brain.

For millennia, seafarers have depended on the sun to know their position in the world, but often the sun is not visible.

Polarisation vision solves that problem, Dickinson said, because if there’s even a small patch of clear sky in a fruit fly’s very broad range of view, then the natural light patterns can provide location information.