Why are moths attracted to light?
The sources I found agreed that moths normally use the moon as a means of orientation and navigation. With their flight pattern, it makes things easier if they have some way of knowing which way is up and the moon provides that for them. Our artificial lights now seem to provide that as well. For navigation, moths use the moon as we used to (and sometimes still) use the North Star. As they fly at night, they head straight in their desired direction with the moon directly overhead. After each hour, they adjust their line of flight about 16 degrees to account for the movement of the moon around the Earth’s surface. (so impressive!)
Most moths that use the moon to navigate (noctuid moths) also have geomagnetic compasses that they use to navigate on moonless nights. This is a more difficult way of navigation, thus it is only used when there is no moon. Nights without a moon are also the times when moths are more likely to congregate at your porch light.
Other interesting details and theories were that moths also use light sources as the direction to safety. Whenever they were in danger, moths would fly towards to moon because that would normally get them away from predators. Now, artificial lights are becoming that for moths in addition to the moon.
Moths are more sensitive to the wavelength of white lights, so they are attracted to them.
Another interesting question on this topic is: Why do moths stay around lights? Moths eyes take a longer time than humans do to adjust to light, so when they hang out around a light and someone turns it off, they are essentially blind for a long time. If they experience this, why would they go near our lights during the darkness? Some possible answers are that they simply forget this experience and therefore continue to do it. Another possibility is that once they get to a light at night, they don’t want to leave because they won’t be able to see if they do.
Finally, the reason a moth that is near a light will fall from the wall if you tap it is that their muscles require some shivering or warming before they are able to fly again.
Hopefully this was interesting, and now you know!
~Agora você konw
[sources include: http://animals.howstuffworks.com/insects/question675.htm and http://butterflies.freeservers.com/moth_light.html and http://www.livescience.com/33156-moths-drawn-artificial-lights.html]