• Story alerts
  • Letter to Editor
  • Pin it

Dear Matt: How good are the elves at figuring out questions that BUG people? Good, I hope, because there are lots of bugs in my brain lately. And around the porch light at my house. They’re the usual suspects. I don’t know what kind they are. I hope that doesn’t matter. Every time you go out the door you get a face full of BUGS. I hate it but it also sort of fascinates me. Why would moths that fly at night be attracted to a porch light? It doesn’t make sense to me. Maybe it does to the elves. If it does, keep hounding them until they spill the beans. I’m very serious about this. I don’t know why, I just am. — Clinton, 3000 Miles Away

If you live where you say you live — back East somewhere — I’d think you’d have tinkly, crinkly little frozen moths stuck to your light bulb. Well, no matter. As it turns out, scientists don’t know your answer, and so far the moths ain’t talkin’. But, as usual, the science guys have some guesses. Good guesses? Maybe not. That’s up to you. As I always say, what would life be without a few little mysteries to give our brains something to chomp on? Here’s your particular hors d’oeuvre, thanks to the house entomologists here in the bug division of the spectacular Matthew Alice Institute for the Study of Weird Stuff in the World Around Us.

We can start by saying that no science guy knows why moths fly in a straight line to your porch light. One thinks he knows why moths fly in a straight line toward a candle, but that’s a different thing. The oldest theory about this moth/porch-light stuff is that moths (most nocturnal) use the moon for navigation, set up an angle of flight relative to the moon, and try to maintain it. When the moth mistakes a porch light for the moon, it flies toward it and eventually has to fly around and around it in order to maintain the proper angle. They wouldn’t need to do this with the very distant moon. Science guys credit a general “confusion” for the moths’ goofy flight around the bulb. After offering this explanation for moth behavior, I can only assume the science guys packed up their PowerPoints and left the room quickly, before anyone could ask probing questions and completely deflate this scientific hot-air balloon.

But if that theory is gradually sinking, consider what one researcher did to solve the puzzle. He tied little plastic foam “boats” by long strings to his moth subjects, set the boats afloat on water, the better to observe moth movements. He, too, found his moths making a beeline for a bulb, screeching to a halt, then flittering back and forth within a certain distance of the bulb. In an effort, I think, to blind us with science, he claims that the moths are trying to stay in a dark band around the bulb, called the Mach band. All animals apparently create this with their eyes. Around any bright light source, there’s a band that appears much darker than the rest of the environment. The Mach band. Since moths associate “dark” with “safe,” they flit around in it until they eventually find their way out of the band and fly away.

That’s really about it, Clinton. Take it or leave it. But to make up for scientific vagueness around your porch light, here’s something more convincing re: moths and candles. Yet another researcher claims to have found that moths drawn to flames are all males. Male moths, he says, use smell and vision to track down female-moth pheromones and get lucky, in moth terms. Burning candles, he says, emit the proper infrared wavelengths and smells to lure unsuspecting males. They swoop in, ready to buy her a drink, and get fried instead. Yet a third set of researchers confirmed their own field observations of moths and forest fires by setting small fires and watching their hand-selected moths immolate themselves. They claim they had seen moths actually walking into the path of forest fires, which sparked their interest in a controlled study of the bizarre behavior.

But we can’t ignore the fact that moths in a dark environment are safest from bats, nighthawks, other night-flying predators, yet they still love that porch light. (There’s one group of soreheads that insists flying toward the moon/a light keeps moths safe from lizards, frogs, and ground-dwelling predators.) Moths are scientifically categorized as having “positive phototaxis” — they go toward light — as opposed to, say, cockroaches, which we all know are negatively phototactic. I’m secretly delighted that something as brainless as a moth has so many smart guys baffled.

  • Story alerts
  • Letter to Editor
  • Pin it

More from SDReader


Sign in to comment

Win a $25 Gift Card to
The Broken Yolk Cafe

Join our newsletter list

Each newsletter subscription means another chance to win!