Confused insects: Moths fly into the light even though they don't want to go there

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Moth: If the light source comes from below, they turn around - and fall

Photo: Sam Fabian

The Romans already knew how to help themselves when they had trouble with moths in the kitchen cupboard: artificial light attracted the animals and helped to catch them, according to a source from the first century AD. But are insects really attracted to light? And why?

A paper published in the scientific magazine “Nature Communications” shows that the relationship between insects and light is different than expected. Researchers have placed reflective markers on moths, dragonflies, fruit flies and other insects. They then filmed the animals using high-speed cameras as they interacted with artificial light sources.

“Insects move very quickly for their body size,” says Samuel Fabian, co-author of the study, in a press video for “Nature” magazine. It's only recently that cameras have come into existence that show the airlines that don't just look like a single, undefined heap.

Tragic mix-up, instead of love for light

The researchers' photographs testify less to a tragic love affair with light than to a tragic mix-up. When close to the light source, the insects correct their flight course - so that their backs point towards the light source. It is very obvious to us where the soil is, says study author Fabian. However, all sorts of gravitational forces acted on insects.

Orientation is needed. In a world without humans, where the sun or moon are the brightest light sources, turning their backs to the light source is an effective way for insects to bring themselves back onto a straight trajectory. In a world with artificial light sources, it can lead to at least dizziness and sometimes even the end of life. The author team's 3D data shows how the insects circle in loops around the light, unable to leave the trajectory again.

If the light source comes from below, they turn around - and fall. The authors also describe the so-called "stalling": If the insects had to fly very steeply upwards in order to stay on course around the light, they repeatedly fall down to lower trajectories because their body structure is not designed for such maneuvers.

Does this solve the mystery of insects and light? Not quite, says Fabian. In addition to alignment with the apparent sky, other factors could influence the flight paths of the insects. To find out more, Fabian wants to research insects that are unimpressed by artificial light. It is also still unclear how the insects behave when they are further away from light sources. In the long term, knowledge about animal behavior could help to stop the extinction of species - quite a few die due to man-made light sources.

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