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Why Are Insects Attracted to Light?

Moths have positive phototaxis, meaning they are naturally attracted to light.
Earthworms have negative phototaxis, meaning they are repelled by exposure to light.
One popular theory is that insects use light as a navigation aid.
Certain insects, such as cockroaches, are repelled by exposure to light.
Cockroaches are nocturnal and repelled by light.
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On any given night, hundreds of moths, flies, and other insects can be seen making endless circles around street lamps and porch lights. This may seem like a exercise in futility or further proof that insects are not very smart, but there are actually several theories on why insects attracted to light make such nightly pilgrimages. There is no single scientific explanation for this behavior, however.

Not all insects that are attracted to light act on those impulses. For some, a bright light source is seen as a emergency beacon, and when in doubt, they will instinctively head for the light, which is generally higher than their current danger-filled position. Moving towards the dark would be seen as a move downward, which can be even worse than not moving at all. Light, for some insects, could be viewed in the same way as air bubbles pointing the way up to the surface water for other creatures.

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Another popular theory is that insects use the light as a navigational aid. An insect flying north, for example, could judge its direction by keeping a natural source of light, such as the sun or moon, on its right side. This method works well as long as the source of light remains constant and at a distance. If an insect encounters a round incandescent porch light, however, it becomes confused by the light source. A moth will continue to circle a light because it instinctively wants to keep the light on a certain side of its body while navigating.

The difference between insects attracted to light and those that are not is a phenomenon known as phototaxis. Certain insects, such as cockroaches or earthworms, have negative phototaxis, meaning they are repelled by exposure to light. Moths, flies, and many other flying insects have positive phototaxis, meaning they are naturally attracted to it.

There is some debate in the scientific community over why a positively phototactic insect will continue to hover around an artificial light source even if natural light becomes available. Some believe that the insect is not actually attracted to the light itself, but the darker areas that surround it. Others suggest the insect's eyes, which often contain multiple lenses, cannot easily adjust from light to dark, leaving the insect vulnerable to predators while night-blind. It may be safer for the insect to remain in the light rather than fly away and become too blind to react to threats and obstacles.

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Discuss this Article

anon297121
Post 60

Many theories here. Most are logical. Others are just guesses. All are interesting.

I would assume that studies can be easily performed on the the theories regarding artificial vs. natural light as a heat or energy source. One theory suggested that the attraction was so strong that it must be tied to a survival mechanism is pretty good, but which one? Even if it disorientation, why? Is light such a powerful guidance system? It almost reminds me of deer caught in the headlights.

Maybe studies involving different types of light, their intensities and color are in order.

anon278694
Post 58

If you can kill the eggs at your bed, that is the key. If you determined heat treatment is too dangerous or expensive, now what? The big picture is you have a ranch. You're raising bed bugs and using your bed as a corral.

First, spray your bed or encase the bed to kill the eggs so you won't be overwhelmed. Second, make sure there are no problems with your bed. Nothing about your bed can be allowed to touch the wall or floor, but the caster wheels. Third, the new corral for the bed bugs is a dim light going 24/7 where the bed bugs can be drawn to and removed with masking tape. Fourth, you spray the ceiling-wall line on two of the most distant walls from the dim light to move the bed bugs toward the light.

Notes: Do not spray near the dim light or any other location; that will create a barrier to keep them from coming to the light. This dim light is most likely for life. As new bed bugs arrive at your home. they will go to the light. Bed bugs are drawn to you, like bees, by your Co2. A fan moving air near your bed will mix your Co2 evenly in your bedroom, making it hard for bed bugs to find you. Every other day, a light spray on your bed caster wheels will protect you. Those in the bed bug business won't be needed anymore. Please beware of biased replies from them.

This method seems to be the "Silver Bullet" for bed bugs. This lure will provide detection, control for the home and car. The poorest people will be able to handle their infestations. This DIY project can be done for a very small cost for parts. This is a very "green" method for all living places and whole house treatment; the hallways will become giant traps. The lights are there, a $5 dimmer switch is needed and spray.

Lightly place DE on hall traffic areas where people put their foot down. Careful: My new kitten made a mistake, near the light. I moved the litter box there. Later I found a live bed bug in it. When the bed bugs stop coming to the light, they're gone, for now. If you have total control, you'll have complete relief. The dim lights double for night lights and bed bug control. Bed bugs are not exclusively nocturnal. When light is used as a lure, this will lead to the downfall of bed bugs. Bed bugs like darkness and subdued light. When you provide subdued light in the darkness they will go there. Just look it up online!

anon272288
Post 57

I observed a light bulb outside of my tent. A fly groomed itself nearby the light, and if another species of insect comes by, the insect that was there first tried to kill itself with the heat. What? This has happened more than a couple times. Why do they do that?

Another thing: the hairs on the back of the fly stood straight up when it was beside the light source. Mating happens a lot around light bulbs too.

I think it's more of a "nine wonders of the world" to insects, making it a 'religious' experience to them since light sources such as this are not natural to their instincts.

A few times the bugs flew hard right into the light, maybe mistaking it for a hole to escape from a dark place.

anon269246
Post 56

I was thinking about the concept of how bees instinctively use the sun as a guide to fetch food, etc. Maybe insects behave like bees in this way, possibly to go to somewhere else. Since the flying insects always go towards the most lit source, which at night is usually a light bulb in a room to find a way out, and they are not finding the way out!

Well was just thinking, but quite unsure about it. At first I thought flies turn around for energy, but this article and the comments convinced me they don't. Nice article!

anon268290
Post 55

I think insects are attracted to the warmth of the light rather than light itself. I've seen tube lights don't attract as much as lamps or bulbs do. I'll go with the theory of refueling.

anon264222
Post 54

Probably because of the same reason only deep sea creatures have their own light.

Georgiyboy
Post 53

Why do we love light? Maybe it makes us feel safe? Have they ever thought of this theory?

anon229887
Post 50

Thank you everyone. I loved your comments. They are helping me with a science project. Now I know I will get an A. Thank you once again.

anon211942
Post 48

It can't be for energy because I'm here at this site because I noticed a stupid bug fly over and over again towards the light, until it got hot enough to burn the thing. As it fell to the ground I was thinking I know that burned because I would've burned my own skin if I stayed that long. It's not for energy purposes.

anon197441
Post 46

I was observing a fly that was annoying me (in my office) fly repeatedly towards the light, then away, then back again (something I've observed a million times in my lifetime) when it struck me that it appeared to be gaining energy.

It was flying much slower than normal and it kept going back to light. It appeared to be "refueling."

That's when I decided to search online to see if anyone else had theory because I never heard it before.

This was the first site I landed on and I see that commenter on Post 42 came to that conclusion as well.

anon165645
Post 44

poster no 42: I do not think flies get energy from light especially if it is artificial. If they were, i think science would have figured it out by now as they did with iguanas.

anon150332
Post 43

maybe they carry little books with them and just want to sit near the light and have a chance to read em. once I saw a fly making other insects pay to be able to use the light service, that greedy bug.

anon139591
Post 42

After observing and photographing a Crane Fly on a incandescent lamp, I arrive at the conclusion that insects are attracted to light to receive energy.

anon127879
Post 41

Maybe they don't come for the fire, but for those who might gather around the fire with them. it could b just a meeting point.

But what about the fly who tried to land on a bulb?

that's a good question. and yes, human beings have the same instinct.

thanks for the article!

anon126576
Post 40

And if there is a new moon? They don't fly at all I guess.

anon122846
Post 39

Moths do orient themselves by moonlight. Some male moths are attracted to candlelight because of similarities in the candlelight to a female moth's pheromone; hence the moth to a flame bit.

But these reasons do not explain the large cross-genus attraction of insects to light in general.

the anons post about reincarnation is interesting. I have personally watched a common house fly buzz around a light bulb, attempting to land on it, get burned over and over only to fly off, rest nearby and then repeat the process until it inevitably dies from its burns. This so intrigued me that I inspected the fly under magnification. I found that the ends of its legs were so dry and brittle that the final fall from the light bulb as it died was enough to cause its exoskeleton around the tips of its legs to crumble.

The instincts the fly is acting on must be of high importance to the fly, mating? food? survival? Perhaps the fly remembers only the light of its maker and that is what it is attempting to rejoin?

anon112564
Post 37

I think that light may be interpreted as heat. Where I live, it gets pretty cold at night, but the incandescent bulb on the porch produces a lot of heat. I hear about the first frost killing off most of the insects in the area, so maybe this is a way of avoiding that?

anon109951
Post 36

I am attracted to light at night too, but that is where it stops. Insects seem to keep banging their heads against the bulb - must give them a headache. Why do they do it?

Someone said insects avoid yellow light - maybe over thousands of years there have been fires some got burnt by fire which is often yellow and decided it was a bad idea. Light bulbs being bad hasn't caught on yet.

anon104607
Post 35

I think light source is like the escape route for positive phototaxis insects. The question of why insects love light comes to my mind as i see a dragonfly hovering around the light source. (Weird though to be able to see a dragonfly at night) but it helps clean the dirty light as the wings move frantically. Quite a useful characteristic of insects. It stops moving now and stays near the light. Just like humans gathering around a fire to keep themselves warm.

Well i did some research on it and dark-adopting mechanism of insects eyes responds much slower than bright-adjusting-mechanism. So they will experience a period of blindness when leaving the light sources.

anon100879
Post 34

This is just my hypothesis, I think insects are attracted to light to charge themselves with energy.

anon97694
Post 32

while a lot of the comments on this article are pretty puerile or ignorant I felt the need to comment on number 13.

Numero 1: You are linking the attraction of insects to light with their survival needs. Lights are just certain objects that disorient them and the fault lies with humans. Before there were no artificial lights, all insects lived undisturbed by our incandescent creations.

Numero 2: Moths do not actually feed on clothes but their larvae do. Before we made clothes they fed on natural fibers a.k.a., plants.

anon94784
Post 31

Humans are naturally attracted to light, too. If it were dark and I saw a source of light coming from somewhere, I would go to it. It's just seen as a means of protection and comfort I guess.

anon94520
Post 30

I live on the outskirts of a big city in the state of Missouri, USA and I just noticed that there are very few bugs flying around the lights at night. Very strange. Normally in July (it's 2010) the lights have swarms of bugs flying around them at night.

I did a internet search; punched in,"Where are the bugs" wondering if others had noticed or had an idea why. I live in a residential area, basically, so I would think one could rule out spraying of crops as the cause. But what could it be? Let me know if you come up with a theory or answer. Till then I will keep on watching.

anon94336
Post 29

Probably because back then light was scarce at night time, while in recent times humans discovered fire and started using it widely and today there's electricity almost everywhere; so the insects don't need to create light because it became very available.

anon92343
Post 28

I'm kind of surprised I don't see the following theory.

Ancient insects, kind of like fireflies used light to find each other, and many of those insects could create light the same way. But the insects of today, can for the most part, not create light, yet are still drawn to the light by instinct.

anon85968
Post 27

Our creators made insects attracted to light so we could use them as easy food around the campfire. They were made naturally attracted so we would not have to expend precious calories when the temperature drops at night to find food. Therefore we just expend the energy to light a camp fire to keep warm and the insects (our food) come to us.

anon85549
Post 26

An earthworm isn't an insect.

anon80060
Post 25

I believe in reincarnation, and since insects are some of the worst creatures you can be reincarnated as I think they are "heading towards the light" because they want to die and be reincarnated again, hopefully as something better than an insect. Just a theory.

anon78811
Post 23

it is nice info. thank you wisegeek.

anon78762
Post 22

I really thank those who did the research and the WISEGEEK that posted the information. Indeed, I have learned a great deal from the article. --Idongesit.

anon78759
Post 21

Thanks for your regular and informative updates. Big thanks to all the contributors!

anon78707
Post 20

Before artificial light there was fire as on torches. A fire will also cause certain insects to be attracted, often to their doom.

anon78595
Post 19

Fairly good article, but I'm curious about something. If a moth keeps the rising moon or sun on its right side to orient it for travel northbound, wouldn't it turn around and fly south when the moon or sun are in descent? And which way would it fly at noon or midnight? Tilted left wing down? I'm just saying...

carpusdiem
Post 18

Can someone tell me why yellow bulbs, yellow light,

will not cause as much attraction to insects?

anon78554
Post 17

This is such a very helpful article indeed. I've been wondering about insects being attracted to lights for long and after reading this, I'd say that I've been served. Thumbs up for wisegeek content creators.

anon78531
Post 16

after reading article i can actually understand the deep buried fact of their attraction. so good information. ansir

anon78528
Post 15

Thanks for the information and regular updates. very insightful.

anon78524
Post 14

The article is good. Sometimes even we never think of these. But throwing light on these sensitive subjects really help particular children for their brain storming.

anon78508
Post 13

Not having read the whole article with attention yet, just a couple of questions: what were insects attracted to before mankind invented artificial light?

And what fabric did clothes moths feed on before mankind wove the first cloth?

anon76491
Post 12

Excellent information. It may be worth noting that some parasitic insects are attracted to body heat, and would be attracted to the hot light bulb as well.

anon74104
Post 10

i had seen so many times insects attracted towards light but i couldn't find any genuine reason to explain it. but after reading article i can actually understand the deep buried fact of their attraction -kriti

anon73183
Post 9

very good info needed for assignment.

anon61141
Post 7

thank you for this information. i need to do some research for my project and this was just what i needed. -n.m :D

anon60431
Post 6

thanks, i needed this for my project.

anon54596
Post 3

this was a a lot of help.

anon45940
Post 2

that was very helpful. i am in an animal behavior class and i wanted to do a report on why moths and other insects behave this way toward light. Most of the websites i went to did not explain, but simply stated that they *are*. I will save this site to my favorites and definitely visit it when in need of help for class assignments. Thank you!

Loen210
Post 1

Thanks so much for posting this article. Although it's frustrating not knowing the full answer this is one of the best responses so far that I've found online.

I notice all the time at night, insects are so attracted to lights, and I hope so much that it is something good for them, not confusion and such. (I'm an animal lover.)Best Wishes, Hana

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