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Comment by SamBam | Hacker News Reader

I think you're misunderstanding GP.

This definitely refutes the theory that insects are trying to escape towards the light, because, as the article shows, insects don't head directly for the light, but instead move orthogonal to it.

But this doesn't mean they can't use moonlight to help with flying. The theory, as I understand it, is that they use a distant light source -- e.g. the daytime sky -- to maintain altitude. There's no reason they couldn't use the moon to do this too.

Again, they would not be flying towards the moon, they'd be keeping the brightest light to their dorsal side. Since the moon is distant, unlike a lamp, this would result in steady flight.

I'm not sure that it confirms whether they use the moon or not, but it seems like a possibility.

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Wait, so it could be a parallax thing?

The moon is in practical terms infinitely far away, and no matter how far the insect flies it won't budge and stay as a stationary feature to localize by.

But do the same with a lamp that's only 3 m away, and keeping it in the same spot can only mean flying around it in circles, towards, or away from it, otherwise it'll move around a lot relative to the insect observer.

The spiraling in might also be a kind of vertigo response as well. Normally the moon only goes up or down in your field of vision if you’re adjusting your angle - pitching or rolling. But an artificial light source moves up or downwards if you’re changing altitude but maintaining attitude. That would make flying up past the light ‘feel like’ pitching away from it, which might cause autonomic steering responses, similar to inner ear/visual conflicts causing humans to stagger and fall over.

Okay, something I'm confused about. "Dorsal side" means, as far as I can tell, your back. So if a fly is keeping its dorsal side facing the moon, that means its back is pointing at the moon.

When the moon's directly overhead, this makes lots of sense. Fly goes around wherever. But if the moon's low on the eastern horizon, would we expect flies to mostly be facing upwards, and mostly flying west?

Doesn’t it just make more sense that they orient their movement in relation to the moon? Doesn’t matter what the specific orientation is — if the moon is 3 inches across and sitting in a room, it’s gonna fuck with the insect’s navigation.

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