Why do moths fly toward artificial light? Is it true that they are looking for the moon?
Here’s the truth. It’s not so much that moths are “looking for the moon”, but they do navigate using the moon. This doesn’t necessarily mean flying towards it though. What moths do instead, is keeping the moon in a certain angle to themselves. To simplify this with a metaphor for readers: imagine that you always have to keep the moon on your left side as you walk. No matter how far you walk, the moon will always be on your left, and you will walk in a straight line. This is because the moon is so far away, that it is basically at what we call an “optical infinity”: the position of the moon relative to you, does not appear to change no matter how far you walk. This is more or less a simplification of how moths manage to orient themselves at night, which may be difficult to do in low-light conditions.
The difference between the moon and artificial light, is that if you walk past an artificial light source, its position relative to you will change. Imagine that you navigate using a street light. You keep a lightbulb to your left side at all times; just like you did the moon earlier in this story. What happens is that you will start going in circles! If you were to keep a lamp post to your left side at all times, you would basically spiral towards it the more you kept walking, instead of go straight ahead, as you would with the moon.
This is why moths end up spiralling towards artificial light sources in what seems like a logarithmic spiral; the angle of the moth relatively unchanging as the insect adjusts its flight path.
One final note: this is a fragment of the true reason moths are attracted to light. It gets more complicated the deeper you look into their biology. For instance, some moths remain on their host plants for their entire adult life, but yet, are attracted to artificial light. Alternatively, moths may head skywards towards natural light, to escape predators or before high-altitude voyages, and more. Although what I mentioned above, is assumed to be one of the main reasons. And also, interestingly, some species are more attracted to artificial lights than others; any hobbyist that likes to go “moth trapping” may be able tell you about species that are quite common, but seldomly seen at artificial light sources. While some of these details have yet to be figured out by scientists, this story above likely explains the primary reason.
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