ELi5: why do moths gravitate toward light during the night, where it’s absent, but nowhere to be found during the day, where it’s plentiful
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I once heard a theory that moths navigate in part by moonlight, but artificial lights confuse them so they fly in circles. If you think about it, the moon is much more stable in space than a lamp relative to a little moth flying around. It would be confusing to me if I could touch the moon too!
Moths use the moon to orient themselves, so other, brighter lights at night cause them to have issues navigating. The moon is far enough away for it to essentially be a constant, enabling the moths to sustain flight in one direction. Human lights aren’t, confusing navigation and resulting in the moths flying in circles around them.
Almost all moth species are nocturnal, meaning they are active at night. They are sleeping during the day and it’s even hypothesized that bright man made lights can result in moths thinking it’s daytime and going to sleep.
There’s very recent, [new research](https://www.nytimes.com/2023/04/27/science/moths-to-a-flame-insects-light.html) on this.
The new, proposed explanation is that moths and other insects use light to orient their up/down axis. Which works fine when the light is high up above, but fails miserably when the brightest light is nearby and low down.
High-speed photography shows that insects tend to flip in flight so that their backs are pointed towards the light. And if the dominant light is bright, close and near ground level, for example, that means that they end up doing paths akin to continual, banking turns around it. So they’re not actually attracted to the light; rather, they’re confused by it in a way that keeps them flying around it.
Why do you turn on a light in a dark room? So you can see.
Why does a moth go towards the light at night? So it can see.
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