Artificial light likes flames have been known to attract moths and many other flying insects at night for centuries. The earliest written records of the behavior date back to the Roman Empire.
New research has now revealed why insects behave this way.
A team at Imperial College London deployed high-resolution motion-capture cameras in the lab and outdoors to track the detailed three-dimensional geometry of insect flight near artificial light.
They found that insects don’t steer directly toward artificial light.
Rather, they turn the backs of their bodies toward light as they approach it. This causes them to fly at right angles to the light source — falling into orbit around it. It produces motions that seem erratic, often stall, and crash to the ground in the attempt.
Under natural sky light, insects instinctively align their backs toward the brightest hemisphere — their best clue to where the sky is — and which way is up. When light is provided from below, insects flip themselves upside down, confirming the theory.
It's conclusive proof that insects are not confusing artificial lights for the moon and trying to navigate by them, or attracted to heat from lights.
It’s a key step in understanding how night lighting may be contributing to insect declines as light pollution increases. Amber, yellow, or red LED outdoor lights attract the fewest insects. So, if possible, avoid using white, blue, or UV outdoor lights, which attract the most bugs.
This Earth Note was written by Diane Hope and produced by KNAU and the Sustainable Communities Program at Northern Arizona University.
