Now, most of us have probably noticed that artificial lighting at night seems to attract insects like bees around honey pots (if that’s an apt analogy). But we couldn’t figure out why, other than maybe the insects mistook the streetlights for the sun and were trying to pass by them. But now, with the help of lightning-fast photography, Sam Fabian of Imperial College London thinks he’s gotten to the bottom of it…
Samuel – The question that was really interesting to us was why bugs appear when you turn off the lights at night. I think almost every human being on the planet has seen it. The problem was that many of the explanations, and much of the discussion around them, didn’t seem to match our understanding of how insects behave. They didn’t seem too happy. So we thought, what is the data? In fact, it turns out there isn’t that much data about how insects fly around lights at night.
Chris – You’re right about this being ubiquitous. Because I have certainly read Greek mythology literature. There, people mentioned that insects are attracted to flames like moths. People have been speculating about what’s going on.
Samuel – There are quite a few theories. Some of them were that insects are inherently attracted to heat. We now know that that’s not actually true, or at least that’s not the effect causing this problem. You can stick out the LEDs and emit much less heat, but you’ll still see so many insects. Another theory was that it had something to do with the animals thinking they were seeing specks of light peeking through the trees and heading towards them, so they tried to escape to where they could see the bright spots. However, if you actually look at the trajectory of insects, they do not fly straight towards the light. In fact, they envision a strange, circuitous path that will lead them toward the light.
Chris – So how did you test it? Did you set up a bonfire or bright lights? What was the experimental setup like, and how did you objectively observe what the insects were actually doing?
Samuel – The way we approached the first question was this compass clue or ultimately ruled it out. One way to approach this was, are you using something as a kind of landmark reference and are you maintaining that? In certain areas, it should most often be placed on the right or left side of the body. Well, if you want to turn off that light and turn on a new light at the exact same time, after a little confusion in the middle, you’ll have to start rotating this other light in the same direction. Please stay on the left. But what I’ve found is that when I actually sit there and switch these lights around, the direction they go around the lights actually changes, and it changes whether the lights are on the left or the right. And they didn’t seem to care which side it was on, which is totally against this compass signal. The light in this example was a UV LED bulb. They hung these and watched the insects fly around them, which they recorded with a high-speed camera. So these are the ones that can take pictures at 500 to 1000 frames per second.
Chris – So, does something emerge from these photos that could explain why insects seem disorientated when you turn the lights on and off? What are they actually doing? They obviously don’t care about right and left, otherwise they would have circled in one direction as you suggested. So what are they doing?
Samuel – I think it really clicked when I had this beautiful subwing moth. When it landed on my hand and took off, ultraviolet light was shining upwards. What happens is that the moth cruises over her UV light and as soon as it passes over the UV bolt, it flips over and falls out of the air. It doesn’t fit with any explanation or theory we currently have. In fact, it is known that animals have a behavioral reaction in which they think the light is empty and upward, and turn away from the light. The sky was the brightest area that insects could see for his 370 million years of flying around. So, assuming the bright area is the sky and therefore above, you can quickly determine which is above. Using “bright spots” to determine which side is facing up is a very robust, simple and beautiful way to solve this problem. This is a really great idea until someone invents street lights, at which point it suddenly isn’t such a good idea.
Chris – Putting all this together, I would argue that what’s happening when that moth or insect goes to a streetlight at night is that they see this as a light source and think it’s the sky. Next, continue changing your position so that your back is facing the light. But why does it rotate in a circle?
Samuel – If they are always leaning their back towards the light, on average they would think that gravity or gravitational acceleration should be pulling them in a different direction. If they tilt their back, it’s like if they had a helicopter or a plane and they just tilted it. Suddenly, their forces become asymmetrical, which causes the animal to drift. Its drift depends on its position relative to the light. But what happens is, especially if there’s very little wind and you’re flying very stable, you end up getting stuck in a very circular orbit. When something like a dragonfly flies around while tilting its body sideways, it can draw a very tight and beautiful circle with a diameter of about 60 centimeters. This creates an asymmetry in the direction the squadron is heading, forcing it to constantly change directions. As they rotate, the light moves relative to them and they keep adjusting it, and they just get stuck in this pile.
Chris – So, when I try to go to sleep at night, the blue bottle in my bedroom won’t stop, is there anything I can do to help? Is there anything I can do to attract better?
Samuel – Sure, we can think of better ways to lure this. What seems important is that wavelength is very important. This is important because wavelength is actually just the color of light, and we know that things like ultraviolet light are very important and affect a variety of insects. But we also think about this in another way. The question is how to ensure night lighting that does not affect insects. Whether you like insects or not, you should be concerned about insects and not want to influence their behavior. This shows that the direction in which you actually shine the light is very important, and if you want to limit the impact on insects, you shouldn’t just shine the light into the atmosphere or to the side. night.