Why Bugs Are Attracted to Light: Biology Behind the Glow

Think back to eighth grade summer camp—oh how we reminisced for earlier times, shared laughters, traded names of our crushes under the stars. But the moment someone switched on a torch, the scene changed. Suddenly, moths, beetles, and all sorts of creepy crawlies swarmed the glow. Ever wonder why they do that? 

Most of us have likely assumed for a long time that insects are simply attracted to light—a belief so common it lends this article its title. However, recent research from Imperial College London suggests a different story: rather than attraction, many flying insects become disoriented and trapped by artificial light sources.

In this article, we will delve into the biological mechanisms behind this phenomenon—tracing how light interferes with insect orientation, revisiting long-held hypotheses, and examining how our obsession with illumination is quietly reshaping ecosystems worldwide.

The Hypotheses That Came Before

For decades, scientists and casual observers alike have proposed theories to explain why flying insects swarm toward artificial light. As a result, four leading hypotheses have persisted as below:

1. The Escape Hypothesis: This theory suggests that insects move toward light as an escape mechanism—a way to flee from predators or dense vegetation, much like the way in which they might aim for a bright gap in foliage (the leaves and branches of plants). Light, in this view, signals an exit or an open path to them.

2. The Celestial Compass Hypothesis: Some species of insects are known to navigate using the moon or other celestial bodies as fixed reference points. In this view, artificial lights are mistaken for these natural cues, causing insects to spiral endlessly around them as they attempt to maintain a constant flight angle. 

3. The Heat Attraction Hypothesis: Others have proposed that insects are drawn to the thermal radiation emitted by light sources, for instance mistaking the warmth of a light bulb for that of a living organism of another natural heat source.

4. The Blinding Hypothesis: Because many insects have eyes adapted for dimly-lit environments, bright artificial illumination may overwhelm their photoreceptors (specialised cells that detect and respond to light which help living organisms see), causing them to fly erratically or crash.

While this article focuses on the newer explanation—the disorientation, or dorsal light response hypothesis as identified by researchers at Imperial College London—it is not to say that these earlier theories are entirely wrong. Each offers partial insight into a complex biological behaviour, though the Imperial study challenges their sufficiency, and reframes our current understanding of how insects perceive light.

Disoriented, Not Drawn: The New Evidence

Researchers from Imperial’s Department of Bioengineering have shown that flying insects are not truly “attracted” to light at all—they are disoriented by it. To an insect, a light source can appear as the sky itself, a false cue signalling which way is “up”. 

To test this, the team built a flight arena capable of tracking insects’ three dimensional flight patterns in response to artificial light. More on the study can be found here, but the results were striking: rather than flying directly toward the light, insects circled, flipped upside down, and sometimes crashed as they tried to keep their backs aligned with the glow. 

This seemingly frenzied behaviour can be explained by what biologists call the dorsal light response, a natural mechanism insects use to orient themselves relative to the brightest part of the sky. Normally, this response allows insects to maintain stable flight aligned with the horizon. It is this mechanism that allows them to navigate consistently at night. But when a lamp or streetlight becomes the brightest point in view, their internal sense of orientation collapses, causing erratic flight patterns and disorientation.

Why It Matters

The discovery does more than write century-old assumptions on our understanding of insects—it deepens our understanding of how artificial light reshapes the natural world, the very foundation of the ecosystems on which we depend.

Understanding how insects respond to artificial light is particularly urgent amid rising light pollution, a growing contributor to global insect declines (Fabian et al.). However, the consequences ripple far beyond the insects themselves. Insects form the foundation of countless ecosystems: they pollinate crops, recycle nutrients, serve as critical food sources for birds, bats, and other animals. Disruption at this level can thus cascade through entire ecological networks.

The next time you see a moth spiralling around a porch light, consider this: it’s not attracted by the glow. It’s disoriented, as lost as we would be in an unfamiliar city without street signs. Instead of swatting it away, pause and watch—it is navigating a world we have unknowingly made brighter, and far more confusing than it was meant to be.

Reference list

Fabian, S.T., Sondhi, Y., Allen, P.E., Theobald, J.C. and Lin, H.-T. (2024). Why flying insects gather at artificial light. Nature Communications, [online] 15(1), p.689. doi:https://doi.org/10.1038/s41467-024-44785-3.

Hirschlag, A. (2024). Why insects are drawn to artificial light at night. [online] www.bbc.com. Available at: https://www.bbc.com/future/article/20240215-why-insects-are-drawn-to-artificial-light-at-night [Accessed 25 Sep. 2025].

London, I.C. (2024). Flying insects become disorientated and trapped by artificial light | Imperial News | Imperial College London. [online] Imperial News. Available at: https://www.imperial.ac.uk/news/251217/flying-insects-become-disorientated-trapped-artificial/ [Accessed 28 Sep. 2025].

Nuwer, R. (2024). Why Insects Are Attracted to Light at Night. [online] Scientific American. Available at: https://www.scientificamerican.com/article/why-insects-are-attracted-to-light-at-night/ [Accessed 28 Sep. 2025].