Why flying insects gather at artificial light

https://www.nature.com/articles/s41467-024-44785-3

by pseudolus • 2 years ago

440 173 2 years ago

Cool study, I've got this question before from my 7yo and had no idea :P

If I'm reading it correctly, insects don't fly toward the light, they turn the front of their body toward it. Under natural light, this helps them fly correctly ("maintain proper flight attitude and control"), but with artificial light they end up just constantly flying around the light source?

sho_hn• 2 years ago

Not the front part, the upper/back part. Otherwise, yes.

rootusrootus• 2 years ago

they turn the front of their body toward it

Google says dorsum is "back or top (dorsal) side". Kinda makes sense that they'd assume light means up.

huydotnet• 2 years ago

The dorsum to the light fact is interesting. And now, watching some random moth to the light vids on Youtube makes more sense to me [1].

[1] https://www.youtube.com/watch?v=OhNpOsTUqzA

elpocko• 2 years ago

Contrary to the expectation of attraction, insects do not steer directly toward the light. Instead, insects turn their dorsum toward the light, generating flight bouts perpendicular to the source. Under natural sky light, tilting the dorsum towards the brightest visual hemisphere helps maintain proper flight attitude and control. Near artificial sources, however, this highly conserved dorsal-light-response can produce continuous steering around the light and trap an insect.

imbnwa• 2 years ago

Fascinating that it has nothing to do with desire, which has tended to be our go-to as humans stretching back in particular to mythology and even antiquity (eg Aristotle IIRC: “things fall back to the ground because they have a desire to do so”)

rcoveson• 2 years ago

Under what conditions would you call this behavior "desire"? Would we need to demonstrate the impossible, that insects have a sense of self and free will?

Do insects desire food, or does the intensity of certain smells simply compel their mouth parts to start moving in a certain way?

wddkcs• 2 years ago

You could still see it as a desire that is being highjacked by our artificial lights. It's an unintentionally wire heading, where our desire for light defeats the insects desire to trust it's 'instruments'.

jjslocum3• 2 years ago

This seems like a pretty important finding, entymology's version of cracking Fermat's Last Theorem. I wonder if there's a Nobel category for entymology.

smaddox• 2 years ago

I read about this explanation years ago. It's not novel. I don't remember where, though... It might have been from Feynman.

dmd• 2 years ago

This explanation is in a Cricket Magazine I have from the mid-80s, so perhaps there's something new here also?

scotty796• 2 years ago

I had a really weird observation. Do you know how in the summer flies tend to enter rooms and circle the middle of it (where usually the turned off light fixture is)? And they seemingly can't or don't want to find open window to leave the room?

At one point for unrelated reasons I replaced light fixture in my room with more than 200W worth of strongest E27 Philips LED lightbulbs I could find (20*1521lumen).

Few flies gathered in the middle of the room as usual during the summer day. Then I turned on this light just out of curiosity. The flies dispersed within seconds, suddenly perfectly capable of not flying in circles. I don't think it was the heat or the discomfortably bright light just scaring them off. Even this amount wasn't as bright as sunny day. I think more light and more distributed light (not just comming from the direction of the window) fixed their navigational abilities somehow.

paiute2• 2 years ago

I was under the impression they confuse lights for stars and it messes with them. So if you simulate the sun the probably don’t get confused. You can but red spectrum lights that also are supposed to be bug friendly

darkwater• 2 years ago

This actually squares with the study, no? I mean, when they are inside - and it's my experience as well - they might take the window as the main source of light and think that's the sky, so they start to fly in circles.

scotty796• 2 years ago

That's probably it. When the "sky" doesn't align with gravity they get confused.

shmeeed2• 2 years ago

The observable effect is true, but I don't think it squares. Circles below the ceiling in the middle of the room aren't perpendicular to the window as a light source.

I see this mostly with one particular type of fly that just loves going around light fixtures, maybe they're sensitive to the EM spectrum rather than visible light?

kevin_thibedeau• 2 years ago

I notice that clouds of gnats will gather at the boundaries between light and shade. Other insects may adopt similar behaviors.

zuzun• 2 years ago

Flies easily fly through the window if it's substantially brighter than the room.

scotty796• 2 years ago

Not in my experience. The walls were dark. And the window was bright occupying half of the surface of one wall. They still flew in circles.

I think it might be what other commenters are pointing out. That flies consider the brightest direction to be the sky, but if it's to the side (with respect to gravity) it messes up their navigation.

NL807• 2 years ago

I have a few theories, these are my own speculations, so I could be wrong.

I speculate that the flies rely on a phenomenon called "optic flow" for navigating around obstacles. Basically the rate of feature movement perceived on each side of their head/compound eyes determines proximity to objects. Their vision is very blurred, so features need to be quite large, or at least contrasting. If you have a dimly lit room, with white walls, the whole space will appear mostly featureless to the fly, until they get close enough to the wall, and thus fly around in circles.

Perhaps they also use a fixed contrasting object as a reference point, like the light fixture (turned off) and return to it if they veer off too far into the "featureless void". If you turn on the light, the perceived illumination in the space is inverted. The light makes previously invisible objects around the room more contrasting for them to navigate about and to fly closer, even land.

switch007• 2 years ago

I’m curious: how are those 20 bulbs installed? You got a single fixture with 20 bulbs??

dclowd99012• 2 years ago

Fixture adapter like this maybe? https://a.co/d/iOgDKZf

scotty796• 2 years ago

Just screwed 20 lightbulb sockets to a board and connected them with wire.

bethekind• 2 years ago

I like bright lights as much as anyone else, could you explain how you got a 20x fixture set up in your room? I've heard of 500 watt E38 mogul fixtures, but not 20x mini ones

scotty796• 2 years ago

I just screwed 20 cheapest lightbulb sockets to a board and connected them with wires.

sschueller• 2 years ago

So one could optimize an outdoor light location design to reduce insects?

Like for example an outdoor dining terrace?

micromacrofoot2• 2 years ago

In my experience... kind of. Light isn't the only thing they're attracted to so you'd have to optimize distance and cover different variables for different bugs.

One fun thing you can do is relocate small swarms of bugs with a torch to another light source. So if you're being pestered, turn on a torch... and slowly walk the bugs to a different light source (a distant lamp for example). Then turn off the torch and walk back to where you were. The light will keep them there.

Simon_ORourke• 2 years ago

Would or could that be automated? We are hounded from late spring to the fall by all kinds of flying nasties at our front porch. Some led string that moved them all away would be awesome!

fasthands9• 2 years ago

Still seems a bit tricky unless you have a ton of land?

Only one experiment that we know of has tracked moth trajectories to lights over long distances, and found only 2 of 50 individuals released 85 m from a light source ended their flight their flight there

I realize this is a small sample, but seems to suggest that if you placed a lamp in a field that 4% of all bugs within a ~football field in every direction would end up near it. I feel like that may mean placing a lamp 10 feet from where you are going to eat (or whatever) may actually attract more insects to that general area.

But I'm having trouble understanding some of their methods

bee_rider• 2 years ago

I’m not sure if there’s interesting optimization to do. Simply: bugs are attracted to light, light=more bugs, no light=fewer bugs. Motion detectors, for example, can make it so that the light is only temporary and you don’t get those moth parties.

stinos• 2 years ago

bugs are attracted to light

Isn't the takeaway from this study that they aren't really, but rather that once they happen to come close to it they cannot get away from it anymore?

paiute2• 2 years ago

Bug bulbs: https://www.amazon.com/Edison-A19-14W-LED-Light/dp/B089QXZ8R...

throw_pm232• 2 years ago

What do you want to reduce further, a large fraction of insect-species are already getting extinct across most of the developed world.

falserum• 2 years ago

May I inquire where do you live? Urban or rural?

phreeza3• 2 years ago

Maybe some sort of directional lighting funnel that attracts insects on one side and the guides them out in a direction away from humans?

alxmng• 2 years ago

Does this explain why bugs seem to swarm at sunset? Because the sun is lower towards the horizon it brings the bugs towards the ground?

beedeebeedee• 2 years ago

Some aquatic insects fly around sunset because the polarization of the light makes it easier to see bodies of water to land on

tomxor• 2 years ago

So now we can blame the insects bad attitude rather than our artificial lights.

nashashmi• 2 years ago

I have a feeling the stars are used by insects to navigate in pitch dark environments. And the lack of stars may be causing a large decline in insect population.

Making a road trip in the light polluted northeast america, I was looking for stars in the darkest of forested of environments, and I could not find any stars anywhere. I am not sure if the clouds were there. But I realize I have not seen stars in a long time.

r2_pilot• 2 years ago

I hope you get the opportunity to see them soon. I live in the south and I enjoy them, although the "seeing" (astronomy term) is poor here due to the jet stream.

chankstein38• 2 years ago

I'd argue that, based on what this paper is discussing at least, it'd be pretty impossible for them to use stars to navigate. I'm not sure what they'd do in pitch dark environments but if they're using either the sun, moon, or artificial light to help them navigate, I highly doubt stars would even register/be detectable to them.

tzs• 2 years ago

It depends on what you count as using stars. Insects don’t have good enough eyes to see individual stars, but dung beetles can see the Milky Way and use it for navigation.

codetrotter2• 2 years ago

So am I understanding correctly that this confirms the common perception they cited:

Insects use the moon as a celestial compass cue to navigate, and mistakenly use artificial light sources instead

mapreduce2• 2 years ago

I don't think it confirms that. It seems to be one of the popular theories they investigated. Later they say -

"In both field and lab conditions, insects rarely head directly towards, but consistently fly orthogonal to the light source. This refutes the fundamental premise of an escape response."

"An insect should keep a light source at a fixed visual location for maintaining its heading. Switching light position (Supplementary Fig. 5) shows that insects readily hold the light source on either side of the body."

It makes sense to me. Imagine you were an insect and you would use the moon for navigation. Would you really be flying directly towards moon? No, right? Then how could someone think that insects flying directly towards artificial light source is the basis for the theory that insects use moon as navigational aid?

SamBam• 2 years ago

I think you're misunderstanding GP.

This definitely refutes the theory that insects are trying to escape towards the light, because, as the article shows, insects don't head directly for the light, but instead move orthogonal to it.

But this doesn't mean they can't use moonlight to help with flying. The theory, as I understand it, is that they use a distant light source -- e.g. the daytime sky -- to maintain altitude. There's no reason they couldn't use the moon to do this too.

Again, they would not be flying towards the moon, they'd be keeping the brightest light to their dorsal side. Since the moon is distant, unlike a lamp, this would result in steady flight.

I'm not sure that it confirms whether they use the moon or not, but it seems like a possibility.

Retr0id• 2 years ago

If your logic is "keep the brightest light source on your left", then for a light source that's nearby (as opposed to "infinitely" far away, like the moon) you'll end up orbiting it.

Depending on your precise navigation logic, you'll either end up with an increasing or decreasing orbit radius. If it decreases, you'll eventually crash into the light source.

rdtsc2• 2 years ago

Imagine you were an insect and you would use the moon for navigation. Would you really be flying directly towards moon? No, right? Then how could someone think that insects flying directly towards artificial light source is the basis for the theory that insects use moon as navigational aid?

If you're flying parallel to the ground (horizontally), you'd want the moon to be where your back is and you'd have a good change of flying straight. It's like when the kids say that the moon seems to "follow" them.

"Dorsal" means where the top part is, the insect's back, as it were.

jgilias• 2 years ago

That’s my understanding too.

The way I thought about this before was that normally an insect would ‘keep the moon’ on one side to navigate straight, but artificial light messes that up and they end up spiraling around those light sources.

Which seems exactly the behavior that they have demonstrated in the research.

pavedwalden• 2 years ago

I think the moon theory was almost right, but I didn't see any reference to insects keeping the light source to one side or the other. The researchers seem to think that insects orient as if the brightest thing they see is "up".

mapreduce2• 2 years ago

they end up spiraling around those light sources

What I'm struggling to understand is how the insects then reach so close to the artificial light. Why don't they spiral the artificial light from a great distance like 1 metre or 2 metres away? I see the insects hovering like millimetres or centimetres away from artificial light.

Berniek2• 2 years ago

Insects use the moon as a celestial compass cue to navigate, and mistakenly use artificial light sources instead

I think that was one of the theories being investigated by this research. The paper demonstrates that it is the actual light (of the moon or stars or sun or artificial source) they use to orientate themselves in the horizontal plain BUT that is not navigation. With a "tilt" in their orientation they will fly in circles around the light but this tilt also causes inefficiencies in their actual flight mechanism so will cause erratic directional stability as their flight path rapidly changes their spacial relationship to the light source. Whatever their navigation imperative (heat, cold pheromones,smell, sight, sound) will be affected by this spacial relationship instability.

_xerces_• 2 years ago

I think a lot of the comments are also missing the fact that the moon is an unreliable means of navigation due it not always being present the whole night (or at all), changes brightness, moves around the sky and can be covered by cloud. It is unlikely then that insects would specifically evolve to use it as a means of navigation.

The paper states that it is the general brightness of the sky, even at night, compared to the ground that is the point of reference. So insect point top side at diffuse bright area and bottom side will be parallel to ground.

conductr• 2 years ago

It seems to me they are using it, but as you mentioned navigation may not be the purpose. There may be none. It may just be that insects that do this congregate and reproduce thus it’s just a mate finding thing that’s evolved. Since insects often have short lives, I’d guess it also explains why they’re always doing it (they need to mate asap).

Might also explain why they don’t go directly to the light but eventually end up there circling it erratically, increased odds of bumping into a mate.

mihaaly2• 2 years ago

More like using the sun/sky to adjust their attitude of flying. Everyday, not only when moon is visible.

teeray• 2 years ago

It’s always amusing in the garden center at Home Depot looking at the enormous spider webs (and the fat spiders) around their sodium vapor lamps. It must be that the number of calories required to produce bioluminescence to create this effect must be greater than the calories that could be derived from hunting that way. But if someone else provided that free energy for hunting…

patall• 2 years ago

Or you are observing evolution in action. A bioluminescent spider would likely be an easy target for birds or bats. One by the lamp is not because hunters have simply not adapted yet. Or maybe, spider webs used to be enormous and profitable everywhere, only that insects dying globally makes them profitable now only in those light spots.

wolverine87613• 2 years ago

Interesting. I sometimes wonder how they end up near the lights: there wouldn't seem to be a light source at night for most of their evolution. Maybe they used the moon in the background.

But is it correct to assume that, if something is naturally possible (e.g., bioluminescence), and provides significant evolutionary advantage, the species will evolve it?

If so, why are we the only intelligent ones (so far)? Why didn't chimpanzees, sharing a common ancestor with us 7 million years ago, evolve intelligence?

xattt2• 2 years ago

My guess is that apes with similar interests started socializing because it was enjoyable and more stimulating than hanging out with apes who could not/would not perceive the nuances of the world the same way.

nsvd• 2 years ago

My guess is that spiders build webs in many places, but only the successful ones remain. In other words, survivor bias.

xattt2• 2 years ago

This spider-webs-covering-lights phenomenon is replaced over and over and over in every Northern Ontario community. It was unreal when I worked at a camp on Lake-of-the-Woods.

I am sure there was enough webs that you could stuff several pillows with them.

blauditore• 2 years ago

The paper tries to make it sound like it solved a long-standing mystery, while it basically just confirms the most obvious explanation: Insects use artificial (close) light sources like a natural (distant) light source for navigation, which makes them eventually spiral towards the light most of the time.

The methodology and resulting graphics are interesting, but the underlying geometry of the effect is not really new or surprising.

martopix• 2 years ago

Yeah, I feel this was taught to me in primary school or something.

henearkr2• 2 years ago

How is it compatible with the times of the day/year when the sun is absolutely not "up there" but closer to the horizon?

ryankrage77• 2 years ago

The insects still orient themselves towards the sky, as it's the brighter hemisphere. They're not locking directly onto light sources, just using them as a cue for orientation. But that fails when the reference point is not distant, as with an artificial light.

henearkr2• 2 years ago

Thanks! I understand better.

krylon3• 2 years ago

I wonder if spiders have fights over who gets to build their net next to that big, bright lantern. Those must be prime real estate for them.

lukan• 2 years ago

Some (or most) spiders are territorial and yes, they do fight for hunting ground.

krylon3• 2 years ago

Makes sense. Thanks for clearing that up! I really do learn something new every day.

swayvil3• 2 years ago

It'a a purely legal form of combat. Lawsuits and contract disputes.

krylon3• 2 years ago

I suppose with up to eight eyes, you can get a lot reading done.

svilen_dobrev• 2 years ago

and how about moonless nights? or thick clouds?

seems there should be alternative navigation ways..

aidenn0• 2 years ago

There may be. I recall a documentary where they were studying homing pigeons. Placing magnets on the pigeons would throw off their navigation, but only on a cloudy day, suggesting that any magnetic navigation they have is redundant with solar navigation.

Berniek2• 2 years ago

Well one other aspect of this research springs to mind.

Most "bug zapper" design are wrong. It should consist of a light source and a single grid perpendicular to the light source rather than surrounding the light source.

The light source should also be constantly varying to ensure the insects' tilt (and hence their circling behavior) will also change the radius of their circles.

wolverine87613• 2 years ago

  And there's this moth outside my kitchen door
  She's bonkers for that bare bulb
  Flying round in circles
  Bashing in her exoskull
  And out in the woods she navigates fine by the moon
  But get her around a light bulb and she's doomed

  She is trying to evolve
  She's just trying to evolve


  Gunnin for high score in the land of dreams
  Morbid bluish-white consumers ogling luminous screens
  On the trail of forgetting
  Cruising without a care
  The jet set won't abide by that pesky jet lag
  And our lives boil down to an hour or two
  When someone pulls a camera out of a bag

  And i am trying to evolve
  Trying to evolve

cmitsakis• 2 years ago

previous discussion https://news.ycombinator.com/item?id=35592654 128 comments

palata3• 2 years ago

What about the color? I know it is slightly orthogonal, but the article says: "This is true even at night, especially at short wavelengths (<450 nm)".

I always wondered: isn't there a light color that we human see and that minimizes the impact on the insects? Say if we only used red light in the cities, would it help?

wolverine87613• 2 years ago

Try different colors at your home!

palata3• 2 years ago

Well I was hoping for something more scientific. I read a bit about that, and it seems like insects are more affected by smaller wavelengths (UV/blue rather than yellow/red) and some species polarized light.

But then if we know it, why don't we engineer the street lights to not attract insects?

JoBrad• 2 years ago

My parents used to use these. I don’t recall if they worked, and I’ve not seen them in quite some time.

https://www.lightbulbs.com/blog/how-do-bug-lights-work

jomohke• 2 years ago

Camping lanterns are still sold with this idea. For instance, I have one of these: https://hardkorr.com/au/product/u-lite-dual-colour-led-lante...

The wavelength of our orange LEDs is 610nm, putting them outside of the spectrum visible to must bugs, but still well inside the boundaries of human vision. As a result, most bugs will not congregate around our orange light because they simply don’t know it is there.

That colour also feels reminiscent of a camp fire, which I've often thought could be related — a bug wouldn't survive long if it flew into fires.

nomoreusernames• 2 years ago

ive seen all types of flying animals fly to a light source, and ive observed a family of lizards feed upon the bug who are attracted to the lamp. the parents taught the baby lizards who now are teenagers. once a big grasshopper flew into the light and passed out and a lizard saw it happen but didnt go down and eat it. lights are on at night and cold nights lizards are dumber and lazier than usual.

Balgair• 2 years ago

One fun thing to do with a swarm of bug near a light is to take out your keys and shake them.

Keys will often ring in the ultrasonic and poorly mimic the frequencies that a lot of bats use.

If you have a population of bats that hunt near you, the bugs will typically just drop. Like, just drop to the ground as fast as they can.

They know the sound of hunting bats and your keys may be just close enough to that sound that they think they're being hunted. So they do the best that they can to get out of the way and go with gravity. At least, that's my theory.

Fun little thing to do as a bet or with the kiddos.

trklausss• 2 years ago

Well you have no sources and you can be full of it. But following the scientific method, I’ll try your hypothesis next chance I have! :D

guappa• 2 years ago

Too bad it's winter and I'll probably forget this before I have a chance to!

JR14272• 2 years ago

If this turns out to not be true, and just said for the amusement of thinking of all the people jiggling their keys at insects, it reminds me of something a friend in high-school said to me:

"If you peel a banana, take a bite off the top, and then poke your index finger in to the middle of it, it will split in to perfect thirds".

Upon trying this, I discovered it was not true, and my friend just wanted to see me stick my finger in a banana...

m463• 2 years ago

some moths have countermeasures

John said, “Listen, you can hear the jammer.” The what? “The jammer,” he said, “Watch the moths.” It turns out the moths, through evolution, had developed their own electronic countermeasures to jam the bat radar.

https://steveblank.com/2009/03/23/if-i-told-you-i%e2%80%99d-...

lfaw• 2 years ago

fascinating! There's also a wikipedia entry: https://en.wikipedia.org/wiki/Echolocation_jamming?useskin=v...

vlz• 2 years ago

Interesting, I heard a story once that you can catch bats with keys: Put a bunch of keys in a sock and throw that in the air. If there is a bat near enough it might dive for and grab the object, then it gets drawn to the ground because the keys are too heavy. There you can catch it if you are quick.

Might be an urban myth, though it seems like it might just work.

ersiees• 2 years ago

more of a rural myth, I guess ;D

hk__22• 2 years ago

Note that depending on your area this might be illegal. In France for example, bats are a protected species and it’s forbidden to kill or capture them.

archerx• 2 years ago

Seems like a great way to get rabies.

xtiansimon• 2 years ago

Camping in Lassen area of Northern California as a kid, I would tease the bats by throwing a ball of tinfoil in the air. The bats would chase it.

mihaaly2• 2 years ago

I need to buy an ultrasonic whistle and experiment with this! :)

cubefox• 2 years ago

Apparently bees also drop when you turn the light off:

https://youtube.com/watch?v=OmG0OT6MWC8

gwern• 2 years ago

Have you ever done that?

fennecfoxy2• 2 years ago

This is also hilarious too: https://www.reddit.com/r/nextfuckinglevel/comments/17jw3gm/d...

xavivives2• 2 years ago

A theory I have is that some may use it as Schelling point [1] to coordinate. For reproduction but maybe other things too.

Similar how the environment conditions after a rain can be the catalyst for ants nuptial flight [2].

[1] https://en.wikipedia.org/wiki/Focal_point_(game_theory)

[2] https://en.wikipedia.org/wiki/Nuptial_flight

phreeza3• 2 years ago

What would the shelling point be before the advent of artificial light though? Can't be the moon. Or do you think it evolved on the human time scale?

xavivives2• 2 years ago

Yeah, I was referring to full moon. Maybe in combination with other environmental variables. Why can't it be?

If that's case the behaviors relying on it have been quite fucked up for some time.

ottoludd• 2 years ago

I've always noticed that sun rays through monofilament fishing line attract dragonflies, yet fails to do so on overcast days.

fennecfoxy2• 2 years ago

Read a bit of it and it does make sense I guess! Looking it up it seems as though insects generally don't have the fancy ear/inner ear that we have as humans seems to sense gravity and velocity through inner ear and pressure against our skin (across our whole body).

Considering that insects don't have our fancy inner ear and can sense touch/pressure on a surface but cannot use this in flight, I guess it does make sense that they'd need some other way to orientate themselves; why grow another organ/sense when eyes already do the job! (Until humans come along and ruin it by discovering fire).

pyinstallwoes• 2 years ago

So Tesla's will do this? /s

tuan• 2 years ago

This reminds me of one of my childhood's favorite activities in Vietnam: catching water bugs late afternoons. I think they are https://en.wikipedia.org/wiki/Lethocerus_indicus, but I might be wrong. That was in the 80s where Vietnam was very underdeveloped. There weren't many street lights and they were usually dim. Our house was right next to a newly built road (which eventually became a highway). That was one of the only few roads with bright street lights. The brightness of the newly installed street lights didn't attract just us kids, but also these water bugs from the rice field on the other side of the road. Once day we were told that these insects are actually edible! I and a few kids on the same block started capturing those insects, put them in jars, and brought them back home :)

Why flying insects gather at artificial light

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