Light confuses insects’ reflexes

Scientists may have finally discovered why insects circle around artificial light sources.

Human-induced light pollution has been identified as one of the main culprits behind the global insect die-off, and scientists urge us to switch off lights to save the important arthropods.

But why do insects flock to artificial light sources in the first place?

According to a common theory, the tiny creatures use the reflected sunlight from the Moon to navigate at night, mistaking the artificial sources for Earth’s natural satellite. But this does not explain why insects that only fly during the day also congregate around light.

Researchers from Imperial College London have filmed insects in the wild to find out what is really behind the light swarms. High-speed cameras and motion capture mapped out the exact motions of many insects around artificial lights.

One of the discoveries made based on the video is that the insects keep their backs to the light, which leads the researchers to conclude that artificial light sources trigger a reflex known as dorsal light response. The reflex, which is found in some fish and many insects, is a kind of short cut for creatures that quickly need to establish which direction is upwards.

Around artificial light sources, the light reflex can cause the insects to orbit the light and become trapped in a deadly spiral, in which their ability to navigate is completely lost. Even in natural environments at times such as dawn or dusk, the reflex can reportedly confuse the small fliers.

The study also revealed that some insect species are not quite as dependent on this reflex, and that fruit flies do not flock around bright lights at all.