Why insects are attracted to light at night

About the episode

If you sit outside for a while in the summer and a lamp or candle is burning somewhere, it often doesn’t take long before the bugs start coming. But why these insects do this, often in quite hysterical flight patterns, has been a mystery for 2,000 years.

Today, researchers believe they have solved this enigma, thanks to the creation of a number of high-tech 3D images. In a preprint, they first reject a number of existing theories.

Do insects use light to move? No. They could see it from their position relative to the light source, which was constantly changing. Do they come out of the fire then? Not as well. Because the lamps in the experiments gave off practically no heat. Are they blinded? No, because they fly according to patterns and not blindly. Are they trying to find their way out of the darkness, like escaping from a dark cave? No, say the researchers, then they would fly straight to it.

What is it then? According to the researchers, the images show that the insects use light to hold their bodies upright. In the wild, they use the glowing sky for this. In artificial light, they just merge. They can fly around the light source and therefore always correct their posture. Sometimes so bad, for example when the light comes from below, that they fall or collide uncontrollably.

The theory is not new, but it has never been argued so convincingly before, answers researcher at the Netherlands Institute of Ecology Kamiel Spoelstra to de Volkskrant.

The hope now is that the findings may help develop artificial light that has a less severe impact on rapidly declining insect populations.

You can find the paper here: Why flying insects congregate in artificial light.