Contrary to myth, nocturnal insects do not fly around artificial lights because they confuse them with the moon or stars. Recent research, filming moths with high-speed cameras, found they use moonlight and starlight to differentiate between "up" and "down" as they fly.

Their erratic flight around your outside light is actually due to them trying to orientate themselves to a nonexistent horizon.

I don't quite get the difference between insects confusing lights with the moon and stars vs using them to orient up and down, which presumably is due to them being like the moon or stars so they can tell which way is up.

It would be nice if they actually described how this research identified what makes them confused, or explained it a bit more.

Also, do inside lights affect insects when curtains are shut (which largely block the light), or is it mostly outside lights and street lights?

[–] FloofahNZ 3 points 4 months ago* (last edited 4 months ago) (4 children)

Here’s another article, this from Scientific American.

Seems there are several hypotheses on why insects are attracted to light, but no one really knows the actual reasons.

[–] Dave 3 points 4 months ago (3 children)

Thanks! It seems this is the same study. It seems the specifics are that insects are not directly attracted to the light, rather they expect a diffuse light source overhead (such as from the moon and stars) and use this to orient themselves. Their primative light detection can't tell the difference between this light and artificial light.

I would say this is more an explanation of how insects confuse artificial lights for moonlight, I wouldn't say it disproves the idea that insects confused artificial light for moonlight.

[–] FloofahNZ 3 points 4 months ago (1 children)

I guess the RNZ article was simply saying that turning off, or down, outside lights will prevent insects from being attracted to them and harmed.

In summer with windows open, we pull curtains before turning inside lights on. Not seen insects on the open window side of the curtain even with a low level through glow visible.

I’m not sure about the moonlight theory. As they will head towards a bright artificial light, why aren’t there clouds of insects heading out into space every bright full-moon?

[–] Dave 3 points 4 months ago* (last edited 4 months ago) (1 children)

It's not that they are heading towards the moon. The overhead moonlight tells them that towards the light is up. They aren't trying to head towards the light, I think one of the articles mentioned insects facing their back to the light. No matter how far they travel, the ground is dark and the sky is slightly lighter, so they can keep themselves level.

With an outdoor light, if they come near it then moving a metre away drastically changes the direction of the light. If they try to keep their back to the light, they end up curving up and around and back towards the light.

It's just a primative orientation system getting messed up by something that wasn't around when they evolved.

[–] FloofahNZ 3 points 4 months ago

Thanks, very interesting.

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