Why insects like moths are so attracted to bright lights

Like a moth to a flame, er, lamp, insects are drawn to bright lights because they confuse the animals' navigational systems.

By Richie Hertzberg
Published 8 Oct 2018, 18:32 BST

It’s a familiar sight, especially in the summertime: moths and other insects gathered around lights like lamps. Often, creatures entrained in such a glow get eaten by predators or overheat.

While common, it’s not immediately obvious: how could insects be so thoroughly tricked, lured to their death by light on such a grand scale?

Like the tragic tale of Romeo and Juliet, the story of the lamp and moth is one of fatal attraction. Being primarily nocturnal creatures, moths evolved to travel by the glimmer of the moon, by a method called transverse orientation.

“[Transverse orientation] is sort of like us keeping the north star in a certain position so we know where we are,” says Jeff Smith, curator of the moth collection at the Bohart Museum of Entomology. In the same way, it’s thought the moths keep the light source at a certain position in relation to their body to guide them, Smith explains.

Enter lamp, stage left

What moth evolution couldn’t account for was the proliferation of 24/7 electric light in our modern world.

Indeed, the day that Thomas Edison patented the lightbulb—January 27, 1880, which paved the way for global distribution of electric illumination—was a dark day in moth history.

“It’s all gone awry because we’ve provided so many artificial moons,” says Lynn Kimsey, professor of entomology at UC Davis.

Elements within moth eyes are tuned to faint light, and act “like miniature telescopes.” Thus when they’re faced with powerful artificial illumination, it can act as a “super-stimulant,” Kimsey says. (Related: These moths drink the tears of sleeping birds)

“When you’ve got really bright lights it’s almost irresistible.

Star-crossed lovers

But what happens when a moth reaches what it thought was the moon? It’s a jarring reality check.

“I knew a guy who owned a Jaguar dealership that had a big mercury-vapour light,” Smith recounts. “Every night they’d fire on the lights and big beetles would come flying to the mercury-vapour lights, [and] land on the ground. In the morning, seagulls were picking them up, hopping on the jaguars… and pooping on the cars.”

The dealership switched to sodium-vapour bulbs because the wave-length of light they emit is much less attractive to the bugs.

Though there is still research to be done to fully understand moth behaviour, scientists do know that lamps have thrown a wrench into the moth’s evolutionary programming.

“[Moths] aren’t the brightest things on this earth,” Kimsey says. “Excuse the pun, but they’re not the brightest bulbs in the pack.”

“You’d think the goal for the night would be to find food or find a mate,” muses Smith. “But I’ve had a moth out on my porch for three days, just sitting next to the light the whole time… If a praying mantis doesn’t eat it, or a frog doesn’t eat it, it might just sit there wasting much of its life.”


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