Have you ever wondered why moths seem irresistibly drawn to porch lights at night? The answer isn’t just a simple attraction to light—it’s a fascinating mystery that’s puzzled researchers for years.
The question of what draws insects to lightbulbs has fascinated scientists for decades.
There have been several competing theories over the years.
Some, such as H.S. Hsiao, suggested that insects used the moon to navigate and mistake manmade light sources for the moon, causing them to become confused. He noted that moths did not fly directly toward the light, as if they were attracted to the light itself, but to a region next to it.
Others posed that flying insects instinctively fly towards bright UV light to steer clear of predators and obstacles in their flight path. Scientists also theorized that they were attracted to thermal radiation or that nocturnal insects’ eyes were too sensitive for artificial light and that they became confused and blinded
No one has been able to provide a complete and provable theory for the phenomenon until relatively recently.
Why Do Insects Fly In Circles Under Lights?
A breakthrough study published by Nature Communications in early 2024 conducted by Samuel T. Fabian et al of Imperial College London has discovered that insects are not attracted to artificial light at all. Instead, it interferes with their internal navigation system.
Nocturnal insects use what is called a dorsal-light-response to orient themselves correctly in space. When an insect flies, its back (dorsal side) is oriented upwards towards a light source (the moon, stars, etc.), which keeps the insect flying normally. Introducing an artificial light source disrupts an insect’s ability to understand which way is up or down.
Any insect unfortunate enough to be in proximity to the light source will be unable to orient themselves correctly. This can cause them to fly in circles or try to fly upside down. Since most species of insect are not able to fly upside down, they can become trapped in or around a light fixture.
How To Get Rid Of Bugs That Are Attracted To Light?
Though insects aren’t attracted to the lights, turning them off when you aren’t using them can help keep passing insects from becoming trapped and disoriented.
There is some evidence to suggest that different wavelengths can be more disruptive than others to insect navigation systems. A 2011 study completed by Frank Van Langevelde et al tested the effect of different spectrums of light on moths and found that lamps with smaller wavelengths (Mercury vapor and high-pressure sodium-Xenon vapor) “attracted” more moths. Choosing lights that have longer waves (red or yellow lights) may decrease the number of insects that get trapped around your fixtures.
Fabian also recommends shrouding your lights and directing them downward to reduce impact on passing insects.