Why moths are attracted to lights

Yesterday was Plant Day, but first I thought I'd share something from last week's arthropod session. One of the entomologists revealed the answer to a something that has puzzled me for a long time: why moths are attracted to lights. It turns out to be a feature of moth navigation that works very well using natural light sources, but isn't well adapted dealing with human ones.

Younger moths navigate at night using light sources in the sky, like stars (older moths switch to using landmarks). Because the stars are so far away, the moth can fly in a straight line by maintaining a constant angle to where the star appears to be:

But artificial lights are significantly closer than stars, so when a moth flies at a constant angle to one it needs to keep compensating for how the light source 'moves', leading it into a spiral:

So, light pollution pulls moths away from their important nightly activities by making them fly in circles until the sun comes up. Do moths a favour by switching off unnecessary lights at night.