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Life Sciences => Plant Sciences, Zoology & Evolution => Topic started by: clintw on 30/08/2005 19:09:58

Title: Why are insects attracted to light?
Post by: clintw on 30/08/2005 19:09:58
Here's a question that I've wondered about for a long time. Why are so many species of nocturnal insects attracted to light?
Thanks,
Clint
Title: Re: insects
Post by: finchbeak on 31/08/2005 03:09:22
That's a very interesting question.
I know that many nocturnal migratory insects - like many moths - are hard-wired to fly at a fixed angle to a bright light in a dark sky.  This works well when the only bright object in the sky (the moon) is effectively infinitely distant; a fixed angle to the moon gives you a reasonably straight flight path over a long distance.  When these moths encounter a street light, though, their system fails them.  A fixed acute angle to a nearby object will cause you to spiral inward toward it.  A moth will even spiral inward toward a candle flame in a dark room until it fries itself.  That's why street lights (especially ones that are isolated in relatively dark locations) tend to attract hordes of moths.
Of course, this answer can't be true for all insects.  It seems like the majority of insects found on my porch light are moths, but there are also many different beetles, including some that I believe are non-migratory.  I don't know.
I'm going outside to turn on my porch light and see who turns up.
Title: Re: insects
Post by: Monox D. I-Fly on 30/08/2016 05:32:00
Well, when people hear about nocturnal insects, they immediately think about mosquitoes. Mosquitoes avoid light, though.
Title: Re: insects
Post by: Atomic-S on 30/08/2016 06:27:18
Quote
A fixed acute angle to a nearby object will cause you to spiral inward toward it.
What does a fixed obtuse angle do?  Why do insects prefer to fly at acute angles? Or do they? Maybe only half the insects are attracted to the light; the other half are repelled. But we see the half that is attracted because they become concentrated in a small space. ???
Title: Re: insects
Post by: Bored chemist on 30/08/2016 21:10:14
Quote from: Atomic-S on 30/08/2016 06:27:18
Quote
A fixed acute angle to a nearby object will cause you to spiral inward toward it.
What does a fixed obtuse angle do?  Why do insects prefer to fly at acute angles? Or do they? Maybe only half the insects are attracted to the light; the other half are repelled. But we see the half that is attracted because they become concentrated in a small space. ???
I'm not sure but I think that an insect that was trying to keep the moon at an obtuse angle to its fly-path would get a pain in the neck from turning round to see that the moon was still in the right direction as it flew away from it.
Title: Re: insects
Post by: RD on 31/08/2016 01:55:46
Quote from: Bored chemist on 30/08/2016 21:10:14
... I think that an insect that was trying to keep the moon at an obtuse angle to its fly-path would get a pain in the neck from turning round to see that the moon was still in the right direction as it flew away from it.

Moth-vision will be close to 360o field-of-view : if the moon was out, it would be difficult for the moth not to see it.   

(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fwww.sciencephoto.com%2Fimage%2F371736%2Flarge%2FZ3550748-Common_clothes_moth%2C_SEM-SPL.jpg&hash=b44f37acc566823c4514ca4a354d516a)
http://www.sciencephoto.com/media/371736/view
Title: Re: Why are insects attracted to light?
Post by: Bored chemist on 31/08/2016 22:04:21
Then a moth which preferred an obtuse angle would spiral away from a light source like a candle.