Artificial lighting sources cause high mortality in various insect populations. In addition to this environmental concern, the attraction of insects to light sources has aroused human curiosity at least since the light bulb was invented. [By the way, Thomas Alva Edison was not the inventor of the incandescent light bulb].
At first glance, it can be believed that the light dazzles (impresses, attracts) the insects, which are blinded and end up dying, in many cases, burned or exhausted.
Another of the explanations disseminated for decades is that insects head towards the light, believing that it is an indicator of a clear path or exit from the dark place in which they are,
A more recognized interpretation in recent years is that insects confuse artificial light with natural light from the moon (or from the twilight from the sun) and lose their sense of orientation.
A team of researchers from the United Kingdom, the United States and Costa Rica have now presented the preliminary results of a study in which they explain in more detail the reason for this phenomenon of fatal attraction of flying insects towards artificial light points. The results of this work have been published on the website bioRxiv, from the Cold Spring Harbor Laboratory,
The authors note that their groundbreaking 3D imaging study of insect trajectories addresses for the first time in detail the classic puzzle of why insects concentrate on sources such as incandescent light bulbs, and now also LED streetlights.
"We found that, at short distances, most insects do not fly directly towards a light source, but rather orthogonally, in flights at about 90 degrees around, the light source, causing the insects to orbit this light source without be able to walk away, even doing inverted [head-down] flights."
Under normal conditions, insects that fly at night -at least many of these species- maintain more or less straight flights, with respect to the ground, thanks to the orientation system they have on their backs. This system is based on the detection of moonlight, so that the insects fly parallel to the ground with the light always in the upper position.
Insects do not "see the light and go towards it directly, to meet it", the authors explain, but by chance, when they fly at night, they come across an artificial light and this becomes their point of reference, that replaces the moon or the solar penumbra.
When this mistake occurs, the insects begin to fly around the reference light, drawing more or less regular orbits. If they get too close to the light and it emits heat, they end up charred. On other occasions, the insects die of exhaustion from running around without going anywhere or are eaten by specialized predators such as geckos.
"Field data suggest that insects orient their dorsal axes toward light sources, and we confirmed this with motion capture recordings of insects in the laboratory," the authors explain. In short, to explain this phenomenon, the authors propose a model of reflex behavior based on the well-documented response to insect dorsal light. In other words, the artificial light source alters the insects' sense of orientation -which is based on detectors on their backs- and they lose their ability to maintain forward flight. "Our experimental evidence and simulations attribute the light trapping mechanism to a disruption of the insect's vertical perception rather than a navigation signal," concludes the team led by Samuel Fabián.
