You've probably seen insects approaching an artificial light source and getting trapped in it. Although this behaviour has intrigued the scientific community for decades, it remains unclear why it occurs. However, a study published last year has offered an insight into why it happens. new explanation supported with various experiments.
As early as 1937, Buddenbrock put forward one of the most popular hypotheses to explain the attraction of insects to artificial light sources: the insects would use the moonlight as a reference for orientation. Due to the great distance from the moon, its rays are perceived as parallelsThis would allow the insects to fly in a straight line by maintaining a constant angle to them. But when they approach a source of artificial lightthe rays would be perceived as divergent and the insects would try to adjust their flight in the same way, which would lead them to spiral towards the light source.
Although this theory has been supported by some observations, such as the disorientation of certain insects when lunar light is blocked or the reduced effectiveness of light traps on nights with a full moon, it has also been supported by a number of other observations. there are facts that contradict it. For example, many species are attracted to ultraviolet (UV) light, which is hardly present in lunar light, and it has been found that insects do not spiral into the light or even come close to it.
Recently, a team of researchers proposed a new hypothesis: for millions of years, the sky has been the brightest part environment for insects, both during the day and at night, and served them as a guide in flightby telling them what "up" is. According to this idea, insects would have "learned" to fly with the back (upper body) towards the light. Artificial lights would confuse their verticality system, causing them to reorient their flight towards the new light source. This explanation was supported by the observation that many insects tend to orient their backs towards the most illuminated area.
To test this hypothesis, the scientists conducted experiments with different light sources, both in the field and in controlled environments, examining the trajectories of different insect species around them. They found that the insects moved perpendicular to the light, facing its back towards the source. This caused them to orbit around the light, stop in mid-air, or even fly inverted. They rarely flew directly towards the light, and no spiral trajectories towards it were observed.
In another experiment in the same study, they shone a sheet of light above and below the insects. When the light came from above, the insects flew normally. However, when the light came from above, the insects flew normally, when light was underneath, they collided against the sheet. Researchers attribute these collisions to a conflict in its guidance system between the direction marked by gravity and the direction marked by the light source.
If you would like to know more details about this study or want to see some of the recordings made by the researchers, you can do so. here.
Understanding why and how insects are attracted to artificial light does not only satisfy our curiosity. In recent decades, research has been conducted to analyse the effect of wavelength, weather conditions and shielding on the attraction of insects to artificial light sources. These studies are aimed at improving the design of insect traps and reducing the impact of artificial lighting, which is considered one of the main causes of decline of insect populations.
References
Dietenberger, M., Jechow, A., et al. (2024). Reducing the fatal attraction of nocturnal insects using tailored and shielded road lights. communications biology, 7(1), 671.
Fabian, S. T., Sondhi, Y., et al. (2024). Why flying insects gather at artificial light. Nature Communications, 15(1), 689.
Gaydecki, P. (2019). Automated moth flight analysis in the vicinity of artificial light. Bulletin of entomological research, 109(1), 127-140.
Nowinszky, L. (2003). The orientation of insects by light-major theories. The Handbook of Light Trapping, 15-18.
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