For centuries, humans have observed a curious phenomenon: insects swarming around artificial lights at night. From campfires to electric bulbs, these tiny creatures seem irresistibly drawn to illuminated areas, often with fatal consequences. Various theories have emerged over time to explain this behavior, but recent scientific research provides a compelling new answer to the question: Why Are Bugs Are Attracted To Light?
Experts and casual observers alike have long pondered this puzzling behavior, offering explanations ranging from heat attraction to mistaking artificial lights for the moon. However, a groundbreaking study published in Nature Communications offers a definitive solution. The research suggests that artificial light sources disrupt insects’ innate orientation mechanism, known as the dorsal light response. This disorientation scrambles their sense of direction, causing them to become trapped in circles around the light.
“Many animals use light as a reference point to orient themselves in space, determining what is up and down,” explains Samuel Fabian, co-lead author of the study and a postdoctoral researcher in entomology at Imperial College London. “Our research connects this fundamental behavior to the perplexing phenomenon of insects gathering at artificial lights, resolving a long-standing puzzle.”
Debunking Old Theories About Insect Attraction to Light
Over the years, scientists have proposed numerous hypotheses to explain why light acts like a magnet for nocturnal insects. One popular idea was that insects instinctively fly towards the brightest point in their vision, mistaking it for the open sky. Another theory suggested they were seeking warmth from the heat emitted by light sources. Still another posited that the intense glare of artificial light might be blinding or disorienting them.
Close up of a moth
Alt text: Oleander Hawkmoth, Daphnis nerii, a nocturnal insect species, exemplifying the common attraction of bugs to artificial light sources at night.
Perhaps the most prevalent theory was that insects confuse artificial lights with celestial bodies like the moon, which they use for navigation. While some insects do navigate using celestial cues, this new research indicates that celestial navigation is not the reason why bugs are attracted to light. According to Yash Sondhi, co-lead author and postdoctoral fellow at the McGuire Center for Lepidoptera and Biodiversity at the Florida Museum of Natural History, their findings point to a different underlying mechanism.
The Dorsal Light Response: A Key to Understanding Bug Behavior Around Lights
To uncover the true reason behind this attraction, the research team conducted experiments in an insect flight arena at Imperial College London. They employed eight high-speed infrared cameras with motion-capture technology to meticulously track the flight paths of 30 insects from three moth and two dragonfly species. Additionally, they observed smaller insects like fruit flies and honeybees, representing six different taxonomic orders, to ensure their findings were broadly applicable across insect species. This data enabled them to create detailed 3D models simulating the insects’ flight trajectories.
The next phase of the research took them to the rainforests of Costa Rica. In collaboration with Pablo Allen of the Council on International Educational Exchange, the team transported heavy camera equipment, lights, and tripods to field sites to study insect behavior in their natural habitat.
Analyzing both quantitative and qualitative data, the researchers found that none of the existing theories adequately explained their observations. “Using advanced tracking technologies and even simple video analysis, we consistently saw insects tilting and flipping upside down, with their backs oriented towards the light as they circled it,” Fabian noted.
The team confirmed that insects were not directly flying towards the light source but rather orbiting it while attempting to keep their backs facing it. This behavior is known as the “dorsal light response.” In natural conditions, this response helps insects maintain a stable flight path aligned with the horizon. However, artificial point sources of light disrupt this mechanism. Insects mistakenly perceive the artificial light as the sky and try to orient themselves accordingly, leading to erratic, circular flight patterns.
“Insects likely use multiple cues to determine ‘up,’ but the direction of light appears to be the dominant factor,” Fabian explains. “Their visual system dictates, ‘You must keep that light over your back.’”
Further supporting their hypothesis, researchers observed that insects exhibited normal flight behavior in both lab and field settings when the light source was diffused and overhead, mimicking natural daylight conditions, rather than a concentrated point source. “This clearly demonstrated that it’s not about attraction to light itself, but rather a fundamental issue of spatial orientation,” Sondhi concluded.
Expert Opinions and Implications for Insect Conservation
Florian Altermatt, an ecologist at the University of Zurich not involved in the study, praised the research for providing “a satisfying answer to a long-standing phenomenon.” He highlighted the elegance of the explanation, noting that “it was actually a rather simple explanation, defying the previous more complex ones.”
Avalon Owens, an entomologist at Harvard University, also unaffiliated with the study, echoed this sentiment, calling it “exciting to have a new observation” on a phenomenon that has intrigued humans for millennia. She emphasized the significance of advancements in high-speed camera technology in enabling this discovery, revealing something “completely undescribed and frankly unexpected.”
Owens suggests future research should explore the universality of this dorsal light response across different insect species. Intriguingly, the study identified two exceptions: oleander hawk moths and Drosophila fruit flies, which flew normally in the presence of light. Fabian suggests that some species might be able to modulate their orientation behavior depending on the context, and further research could unravel these variations.
For most nocturnal flying insects, however, these findings underscore the detrimental impact of artificial light on their survival. “Insects have been navigating the night sky for 370 million years,” Fabian points out. “It’s only in the last 150 years, with the proliferation of artificial light, that this has become a serious problem for them.” Understanding why bugs are attracted to light in this new context highlights the urgent need to mitigate light pollution to protect insect populations and nocturnal ecosystems.
