Why are Insects Attracted to Light?

You know when you’re outside at night with
some lights on, and insects start flying straight into the light, and swarming around it? It’s a thing! What is the deal with that? Turns out, nobody knows for sure. But there are a few theories that suggest
that electric lights, fires, and other bright, glowing things might confuse the natural instincts
of these insects. Insects that are drawn to light are known
as positively phototactic – and one of the theories behind their behavior is that these
insects use the moon to navigate at night. These insect species tend to be nocturnal,
and many are migratory. So in order to stay on track while travelling
long distances, they want to stay at a specific angle with respect to the moon. So the theory is that these insects mistake
a point of light they find in the dark – like an electric light – for the moon. This could also explain why certain insects
tend to fly wild circles around our lights: Once they reach the glowing object that they
think is the the moon, they keep drastically changing their angles to the light source,
which throws them for a loop, literally. There are some problems with this theory,
though: For one, not all of positively phototactic insects are migratory, and not all of those
use the moon to navigate. Plus, this doesn’t really explain why they
would head straight toward a light, since they don’t fly directly at the moon. So, there’s another theory, which has more
to do with short-term protection than long-distance navigation. Light can also be a sign of an unobstructed
path, which is a good thing if you’re trying to escape a predator, or just get to Point
B. So if insects think a light is a sign of an
obstacle-free area, you can see why they’d want to head straight for it. And it also explains why they might fly straight
into a bug zapper or a fire, because they don’t expect the light source to be so close. Another thing to consider: Many insects are
really good at detecting ultraviolet light – an ability that lots of flowers exploit
by reflecting UV light to attract them. So positively phototactic insects might aim
for your lamp or campfire because they instinctively think it’s something they want, like a source
of food! Which, of course, makes me feel quite sorry
for them. But the next time you see an insect slamming
into a lamp, keep in mind that not even entomologists are quite sure why it’s doing that. Maybe with some more research, we’ll figure
it out. Thanks for asking, and thanks especially to
all of our patrons on Patreon who keep these answers coming. If you’d like to submit questions to be
answered, or get some videos a few days early, go to patreon.com/scishow. And don’t forget to go to youtube.com/scishow
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100 thoughts on “Why are Insects Attracted to Light?


  2. Is anyone watching this after killing a moth that flew in your room. Cause I know I am

  3. Does anyone else has the feeling that this video will explode because of the new moth meme?

  4. Light is just amazing, I don’t think I should have to explain this to you.

  5. https://youtu.be/KUddy8RGwns
    Mike Steven's poetic hypothesis makes sense to me at least more sense than his. Great episode, you should watch the entire vid but the bug/light part comes sometime after the halfway point.

  6. The real question is why I'm using YouTube and not Google.

  7. Insects aren't particularly intelligent, having fewer brain cells than most animals. Ever notice how a dog will bark "I see you" and repeat, and repeat for many minutes. That is repetitive, obsessive behavior. The bright light is a beacon, possibly a source of food that the insect becomes fixated with. Without much memory in the insect, it becomes obsessed. This is a great example of how OCD can be destructive to people.

  8. A virus infecting the insects cause them to find a light and exhaust them self’s to death where the virus is infested by ants maybe?

  9. An explanation I read many years ago also goes along with the confused navigation theory and is still the most convincing theory in my opinion. First thing though, moths don't generally fly directly into the light but in a path that sort of circles around the light ever more closely until they fly into it. So the explanation is that the compound eyes of insects act as wavefront sensors. Light coming from a distant source, like the sun or moon, for example, will have flat wavefront whereas light coming from a nearby light source, like for example, a candle in your bedroom, will have a curved wavefront. When a moth flies by a candle it alters its flight path so that the wavefront will appear flat. But by doing so it again increases the curvature of the wavefront and the moth keeps changing its flight path accordingly until it at last it flies into the flame.This theory is supported by the fact that aberrometers, which are wavefront sensors used in astronomy and ophthalmology, are composed of an array multiple lenslets similar to the eyes of insects.

  10. There are a lot of insects in our light bulb now thats why we closed all the lights and my phone is not that bright but its rare

  11. obviously these bugs cant tell the difference between night and day. when night hits they they think theyve been encapsulated in a trap and attempt to escape back to the daylight by heading for the light. they are mistaking lights for the sun and a way out of the dark

  12. I have trees outside … They're flowering I'm getting moths now I'm getting spiders I think the spiders figured it out …. It's mosquito season so idc

  13. Im just thinking why cant the flies or other insects just go towards the Sun if they are soooo attract with the light to much?

  14. Bull! Bees fly during the day, but if you turn on your porch light they come and play with the bulb!!! So obviously they do not use the moon to navigate!!!

  15. Who else is watching this with some big ass insect flying around your light

  16. im now saying ‘YOU NOCTURNAL I N S E C T’ to all the bugs flying around my tv screen at 12:00am

  17. But none of the theories mentioned in the video address the phenomena of how insects are more attracted to cold light than warmer hues and how heat emitted by the light source is also a factor. I don't really have any particular knowledge on the subject, but I read articles about how 'none heat' emitting LEDs with a warm hue don't attract insects nearly as much as traditional incandescent bulbs.

  18. Earwigs oh God they fly around lights. I just let them out but they freak me out.

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