Why flying insects gather at artificial light

[Balgair]

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.

[vlz]

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.

[m463]

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-...

[trklausss]

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

[fennecfoxy]

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

[cubefox]

Apparently bees also drop when you turn the light off:

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

[mihaaly]

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

[gwern]

Have you ever done that?

[scotty79]

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.

[codetrotter]

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

[_xerces_]

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.

[mapreduce]

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?

[jgilias]

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.

[Berniek]

>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.

[mihaaly]

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

[huydotnet]

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

[andrewgioia]

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?

[rootusrootus]

> 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.

[sho_hn]

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

[teeray]

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]

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.

[wolverine876]

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?

[xattt]

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.

[palata]

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?

[JoBrad]

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

[wolverine876]

Try different colors at your home!

[tuan]

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 :)

[wolverine876]

  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

[fennecfoxy]

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]

So Tesla's will do this? /s

[sschueller]

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

Like for example an outdoor dining terrace?

[Berniek]

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.

[alxmng]

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]

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

[imbnwa]

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]

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]

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'.

[xavivives]

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

[cmitsakis]

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

[nashashmi]

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.

[chankstein38]

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]

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.

[r2_pilot]

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.

[krylon]

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.

[ottoludd]

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