Why do moths fly into lights?

[Cuddles]

I would assume that they are normally attracted to natural light sources, but I can't work out which ones, or why they'd want to bang their heads against them repeatedly. The only sources I can think of are the Sun, Moon and reflective surfaces like water. The first two are out, for obvious reasons. Although most insects are probably light enough to stand on water, the speed they fly into lights seems much too fast for this and I'm fairly sure they'd drown. I could understand them just being attracted to light, but not flying into it for a whole evening. Why do they hate artificial lights so much?

 

[CFLarsen]

It's a Near Death Experience.

A real one, too....

 

[SteveGrenard]

When insects fly at night they use light sources such as the moon for navigation. Light from a distant source reaches both eyes with the same intensity. This enables the insect to fly in a straight line with both wings beating at the same rate.

If the light is from a closer source such as a candle or lantern, it changes the insect's perception. The light is perceived stronger in one eye than in the other eye. This causes the wing on one side to move faster. The insect then begins to approach the light in a spiral path, eventually drawing them into the light itself.

http://www.suite101.com/article.cfm/science_for_kids/11252

 

[CFLarsen]

As usual, Richard Dawkins has the answer:

Moths fly into the candle flame, and it does not look like an accident. They go out of their way to make a burnt offering of themselves. We could label it “self-immolation behavior” and wonder how Darwinian natural selection could possibly favor it. My point, again, is that we need to rewrite the question before we can even attempt an intelligent answer. It is not suicide. Apparent suicide emerges as an inadvertent side effect. Artificial light is a recent arrival on the night scene. Until recently, the only night-lights were the moon and the stars. Being at optical infinity, their rays are parallel, which makes them ideal compasses. Insects are known to use celestial objects to steer accurately in a straight line. The insect nervous system is adept at setting up a temporary rule of thumb such as, “Steer a course such that the light rays hit your eye at an angle of 30°.” Since insects have compound eyes, this will amount to favoring a particular ommatidium (individual optical tube radiating out from the center of the compound eye). However, the light compass relies critically on the celestial object being at optical infinity. If it is not, the rays are not parallel but diverge like the spokes of a wheel. A nervous system using a 30° rule of thumb to a candle, as though it were the moon, will steer its moth, in a neat logarithmic spiral, into the flame. It is still, on average, a good rule of thumb. We do not notice the hundreds of moths who are silently and effectively steering by the moon or a bright star or even the lights of a distant city. We see only moths hurling themselves at our lights, and we ask the wrong question. Why are all these moths committing suicide? Instead, we should ask why they have nervous systems that steer by maintaining an automatic fixed angle to light rays, a tactic that we only notice on the occasions when it goes wrong. When the question is rephrased, the mystery evaporates. It never was right to call it suicide.
What Use is Religion?

 

[Deetee]

Conventional wisdom says they "navigate" or migrate using the moon as a reference point, and since some artificial light sources are brighter, they get "drawn in" towards the light since they try to keep it fixed in the same relative position as thety fly.

This explanation has never properly satisfied me. Do moths all have an urge to go flying off anytime there is a full moon? Where the hell are they meant to be flying to anyhow? Do moths really migrate anyway?

What about moths and their normal activities? - Surely this would be impossible if every time there was a moon in the sky the entire moth population flew away? I cannot see Mikey moth waking up hungry one night and heading for his favourite flower patch only to realise the moon has risen, and being compelled to go chasing rainbows (as it were).

 

[Cuddles]

Thanks guys. I suppose I should have thought of that since it's similar to how bees manage not to crash, just using a big light instead of the ground.

 

[Capsid]

Is is that the moths are looking for nectar and are guided towards plants that have petals which reflect ultra violet light? That doesn't explain what moths do on moonless nights before man came along or is starlight enough?

 

[EGarrett]

Conventional wisdom says they "navigate" or migrate using the moon as a reference point, and since some artificial light sources are brighter, they get "drawn in" towards the light since they try to keep it fixed in the same relative position as thety fly.

This explanation has never properly satisfied me. Do moths all have an urge to go flying off anytime there is a full moon? Where the hell are they meant to be flying to anyhow? Do moths really migrate anyway?

What about moths and their normal activities? - Surely this would be impossible if every time there was a moon in the sky the entire moth population flew away? I cannot see Mikey moth waking up hungry one night and heading for his favourite flower patch only to realise the moon has risen, and being compelled to go chasing rainbows (as it were).

Why are you assuming all the moths do it? Maybe it's just all the moths trying to go somewhere at that moment. After all, the ones attracted to the light make themselves known...the ones that are sleeping or comfortably eating your clothes are tucked away where you don't notice them...

And let me add that this thread has now ruined Mothra for me. There's no way he could effectively battle Godzilla with all those city lights around. Dammit!

 

[Haywire]

Because it's too far to drive.

 

[Deetee]

Why are you assuming all the moths do it? Maybe it's just all the moths trying to go somewhere at that moment. After all, the ones attracted to the light make themselves known...the ones that are sleeping or comfortably eating your clothes are tucked away where you don't notice them...

All observable facts fit with the theory that moths are just attracted to bright lights. Lots of creatures are. Surely there is no need to bring strange lunar-driven "migration instinct" theories into it, particularly when these do not stand up to closer scrutiny.

 

[RenaissanceBiker]

And let me add that this thread has now ruined Mothra for me. There's no way he could effectively battle Godzilla with all those city lights around. Dammit!

Also, every time Godzilla would use his nukular fire breath Mothra would just fly right into it. You shouldn't have to "suspend your disbelief" to enjoy a good documentary.

 

[Modified]

All observable facts fit with the theory that moths are just attracted to bright lights. Lots of creatures are. Surely there is no need to bring strange lunar-driven "migration instinct" theories into it, particularly when these do not stand up to closer scrutiny.

Take a good look and you'll notice that most of them spiral in toward the light. If I was lost in the woods and someone replaced the sun with a big bright light that was only five miles away, I might do the same thing.

Most animals that are "attracted to light" either eat bugs or eat things that eat bugs.

 

[Deetee]

Take a good look and you'll notice that most of them spiral in toward the light.

Maybe so, but there are possibly explanations other than contriving a migratory "navigational-constant-angle-to-the-prevailing-light-source" theory to explain it. Sometimes the moths circle around the light - perhaps experience has taught them that landing on the hot glass is not very comfortable?

I assume that in an pre-electric light world, there would be mass nocturnal migrations of moths (and other insects) all flying off into the distance trying to get "somewhere", this unidentified and never to be reached place varying in direction from night to night and depending upon the time of night according to the position of the moon in the night sky. What an utterly pointless exercise. Where are they meant to be going?

Most animals that are "attracted to light" either eat bugs or eat things that eat bugs.

Do you have a theory for why bugs are attracted to bright lights, or are they all undergoing migrations?

 

[EGarrett]

It's obvious that DeeTee is just a Bat trying to downplay the Moth's sophisticated navigational instinct.

 

[Capsid]

Do you have a theory for why bugs are attracted to bright lights, or are they all undergoing migrations?

What do you think of my proposition that they are seeking out reflected UV light on petals which attract pollinators?

Look here for example.

 

[Deetee]

What do you think of my proposition that they are seeking out reflected UV light on petals which attract pollinators?

Look here for example.

Certainly moths seem to be attracted to UV light preferentially over other bands in the light spectrum. A much better theory IMHO.

Here is a little applet I found which you might like to try - I am afraid my browser will not play it.

I am not saying moths do not navigate when they migrate by the light of the silvery moon, just that this does not explain to me their attraction to artificial light sources.

 

[Capsid]

Certainly moths seem to be attracted to UV light preferentially over other bands in the light spectrum. A much better theory IMHO.

Here is a little applet I found which you might like to try - I am afraid my browser will not play it.

I am not saying moths do not navigate when they migrate by the light of the silvery moon, just that this does not explain to me their attraction to artificial light sources.

But an artificial light source would also emit UV? If so it's not surprising that they would find them so attractive.

Also, I suppose that moths are attracted to flowers by scent (they have large antennae for scent/pheromone detection) and many flowers emit their scent later in the day. This would allow them to find flowers on moonless nights although perhaps not as efficiently.

 

[Donn]

On the "angle to the light" theory - it seems to make sense to me. I am a moth, I'm on a tree. I see a distant flower. I face that direction and I sense the angle of the light in my eyes (perhaps it's a brightness I sense). If I take-off and fly, keeping my head into the light with that same brightness, then I know that I am on a direct line to the flower.

Why I can't just fly towards the flower that I saw (with my eyes) in the first place is a little perplexing! And if it's dark and I can't see my destination, then what matters if I fly in a straight line?
ETA: I meant if it's dark and I can't see the flower in the first place, then how does a straight line help me?

 

[Silly Green Monkey]

I think the problem here is marked in Deetee's first post. Navigation is not migration, though navigation is essential for migration. We navigate by landmarks, but are we migrating? The moths don't need to be taking cross-continental journeys to use lights as reference points. They can just be trying to move from one tree to another.

Donn, insect eyes and brains are very different from vertebrate eyes and brains. For example, one beetle can run faster than it can process light.

 

[Donn]

That's amazing, which insect is it.
Any idea how a moth "sees"? I mean, assuming my example above is close to right, and combined with what you say, then the moth sees the flower (sort of), takes a reading on the light angle and then flies without properly seeing the flower.
I'm guessing that it must switch on it's vision every now and then in order to judge it's proximity to the flower.