Many flying insects fly directly into a light-bulb & end up dead. There are some interesting theories, but scientists and researchers are not at all in agreement about these.
An organism’s response to light with motion is known as phototaxis. Positively phototactic organisms, such as moths and flies, move towards light sources.
Negatively phototactic organisms, on the other hand, move away from light. Like cockroaches that scuttle into a dark corner when you switch the light on. Mosquitoes are attracted to light, but will then hide in some dark corner or beneath furniture; in order to bite you unseen.
Outdoor insects, however, they move towards the light. One theory is that moths and other nocturnal insects use the moonlight to navigate their way around.
This light-angle is constant as the insect flies because the moon is so distant. When a month or night-flying insect flies towards the artificial light, like candles or bulbs, they try to align themselves with the light-source and end up flying in circles.
Yet another, perhaps more logical, the theory is that flying insects attracted to light see an unobstructed light source as a beacon that indicates that their pathway is clear. Therefore insects fly directly towards the light source, to avoid obstacles. Of course, to us, it seems they are kamikazeing or committing suicide!
More theories about flying insects
Flying insects seem to be more attracted to artificial light sources that also emit UV light. They are more attracted to UV light than yellow or red light. Since flowers reflect UV light, one theory says, insects may mistake it for flowers (a food source).
Candle flames have similar light to the light from pheromones of female moths. One entomologist suggested that male moths dive into a candle-flame, as they think it is a female moth looking for a mate (instead of getting lucky, they burn themselves to death).
There is no single scientific explanation as to why moths and flies circle around a street light at night. Some scientists suggest that the insect’s eyes, which frequently contain composite multiple-lenses, cannot easily adjust from light to dark, which leaves the insect vulnerable to predators while flying “night blind”, as it were. Thus it may be safer for the insect to remain in the light, rather than fly away into the dark and be too “night-blind” to react to obstacles and other threats.
A greater understanding of why insects like flies, flying ants, and many beetles are attracted to artificial light could help to develop more effective insect light traps, like fly-killers. This would constantly help the hotel, food and hospitality industry in a big way.
LED light produce UV-A as intense beams of light, which penetrate further than phosphorus lamps. House flies are particularly attracted to LED (UV-A) as their eyes are sensitive to light at that particular wavelength.