Why are insects attracted to artificial lights?

The classic summer cookout comes with chips, drinks and then, after the sun goes down, swarms of insects flitting around porch lights. But flying around artificial lights can have deadly consequences for critters such as moths, gnats and mosquitos; they can get trapped under lampshades and exposed to predators such as beetles, spiders, bats and birds. 

This "stupid circling" can even distract insects from goals such as eating, mating and reproducing, said Avalon Owens, a fellow at Harvard University. And artificial lights may be contributing to shrinking insect populations worldwide. So, given the risks, why are insects attracted to artificial lights? 

Theories abound. Perhaps moths use the moon for navigation, and lights look like the moon. Maybe insects are trying to escape toward the light — or trying to find the dark. Due to an optical illusion called mach bands, Owens said, "the edge of a lit area will appear darker than the rest of the darkness." 

In 1965, one researcher hypothesized that lights might somehow mimic mating pheromones. "That was a wild theory!" said Yash Sondhi, a postdoctoral researcher at the Florida Museum of Natural History who studies moths and sensory systems. "But at that point, all the theories had no evidence," he told Live Science. 

Related: Why are flies so hard to swat?

On one level, it appears that insects fly to artificial lights because older evolutionary responses are being hijacked. "For the vast majority of evolutionary history," Owens said, "the night has been almost entirely dark."

Specific hypotheses are difficult to test because insects in flight are hard to observe. New technologies may finally bring better answers. In a 2024 study published in the journal Nature Communications, Sondhi, along with Samuel Fabian at Imperial College London and other researchers, filmed moths, dragoNFLies and other insects with a high-speed camera. They noticed something unexpected: The moths and dragoNFLies kept their backs to the light as much as possible. They also flipped upside down.