Like Moths to a Flame...

Polyphemus Moth outside the Pinkham Notch Visitor Center

Last week at one of the AMC huts, I was tucked away in my bed unable to sleep. Careful not to disturb my (loudly!) snoring neighbors, I turned on my headlamp to read. After a minute, I found myself bombarded with the fluttering of fuzzy little wings. I resigned myself to turning off my headlamp to avoid this nuisance, but also found myself grateful to have a sense of direction better than a moth.

“Like moths to a flame”, or so the saying goes. You’d think that this self destructive behavior would have been weeded out over thousands of years of fires, candles and lanterns. However, the attraction towards light in moths and other nocturnal insects has a more functional purpose beyond leading them to a fiery death. Like sailors and pirates, moths use using celestial navigation at night- traveling at a constant angle to the brightest object in the night sky. For the past couple millennia, this object has been the moon and, because it is so far away, traveling at a constant angular direction in relation to it allows the moth to travel in a straight line. Similarly, if you were to drive your car, keeping the moon on your right, your direction of travel over a short period of time would be nearly straight.

Enter man made light. Lamps and campfires create a light brighter than any celestial body. Moths, confusing this man-made luminosity for the moon try navigate their way through the night by maintaining an angular relationship to these brighter objects. Unfortunately, these objects are too close to allow moths to maintain a straight line of flight. Instead, the moths spiral in towards the light, fluttering in heat and confusion.

So really, it is just a lesson in simple geometry and evolution has conserved this behavior for a very good reason. But if your brain can’t tell the difference between the moon and a head lamp, then the situation becomes a bit more complicated. As annoying as those moths may be, I have a greater appreciation for the moon, my headlamp, and the ability to tell them apart.

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