Why do moths circle bulbs? Insects are not actually “attracted to flame”

Nocturnal insects are not attracted to the glare of light, but rather disorientated by it, American researchers have determined, pointing out that light pollution can have negative effects on the habitat of these creatures.

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Using surveillance cameras with motion sensors and filming with infrared lighting so as not to disturb the creatures' vision, the researchers showed that when the insects flew around a light source, they tilted their backs toward the light and maintained their body position in that direction. This method of orientation caused their flight to be in several directions, creating the strange trajectories, according to a study published on January 30 in the journal Nature Communications, cited by CNN.

When artificial light does not interfere, nocturnal insects keep their backs facing whichever direction is brightest, which is usually the sky. This evolutionary trick helped the creatures to know where the sky was and to maintain a certain level during flight. However, when insects pass an artificial light source, they become disoriented, thinking the man-made illumination is the sky, said study co-lead author Samuel Fabian, an entomologist and postdoctoral researcher in the department of bioengineering at Imperial College London.

The researchers compiled hundreds of slow-motion videos capturing the behavior of butterflies, moths, bees, wasps, dragonflies and zygopters and found that they were not attracted to distant lights, but became disoriented if there was a light source nearby.

The researchers observed three common characteristics when the insects were near a light source: they orbited, froze, and turned upside down, falling to the ground.

Scientists did an experiment, imitating the sky: they placed a white sheet under a light source and found that insects could fly under it without problems, thus proving that they are not looking for light.

The study thus disproves theories that insects fly chaotically around light sources attracted by heat, or that they mistake the light for the moon, which they use as a compass indicator, since the creatures do not fly directly towards the light.

Researcher: If you don't need a light, turn it off

A better understanding of the impact of artificial light on these winged creatures is crucial, as light pollution plays an increasing role in the decline of global insect populations, the researchers wrote.

Artificial light has several harmful effects on wildlife, including habitat loss and fragmentation, according to a March 2022 article cited by the United States' National Wildlife Federation.

The authors of the new study noted that “light pollution” is a cause of the insects' decline, citing a September 2020 report that found that artificial light affected moth behavior in terms of reproduction and larval development.

The new findings could help minimize the effects of light pollution on insects, said entomologist Jason Dombroskie, manager of Cornell University's Insect Collection and Insect Diagnostic Laboratory.I always say that if you don't need a light, turn it off.” claimed the scientist.