“Like a moth towards the flame”: the attraction of night insects, such as mosses, flies and beetles, towards the sources of artificial light It is so known that it is proverbial. But why are they attracted by light? Actually, they do not fly “towards” a light that attracts them, But rather they turn around! The most accredited hypothesis is that insects use natural light sources (such as the moon) for orientate in the dark, keeping a stable route thanks to the direction of the rays. But the sources of artificial light, much closer and more numerous, confuse The insects, which find themselves flying disorderly around the light in an attempt to adjust the route. This theory was confirmed by a recent study published on Nature, who showed how night insects tend to turn the back towards light to orient themselves; This leads to disorientation And chaotic flight when the light source of reference is very close.
How come insects are attracted to light: night orientation
We are not the first to ask ourselves this question. The first references written to this behavior are found in the ancient Persian poems, and the use of a bright trap To capture Falene (a stratagem still used today by entomologists) is even mentioned in the writings of the Latin agronomist Columella, dating back to 60 AD
The most accredited theory on why night insects are attracted by the light has to do with theorientation. According to this explanation, night insects would use sources of natural light (such as the moon and the stars) as a point of reference. These are sources of “fixed” light: their distance with our planet means that the corner with which their rays reach the ground is constant. The insect would thus be able to align with this stable corner, as if it had a “Natural compass “ which points not towards the north, but towards the light above.
This orientation mechanism has evolved over millions of years, but the recent introduction of artificial lights – like bulbs, lampposts and other electrical devices – has compromised it. In fact, these sources of light are much closer than the moon and for this reason they project rays in all directionsnot in parallel. And being closer than the natural ones, they end up dominating them in intensity in the eyes of insects. Trying to apply the same orientation principle, the latter are in difficulty: in an attempt to maintain a constant corner With a light that surrounds them from each side, the insects end up flying in a chaotic way, often in trajectories a spiral.
Confirmations to the theory on the disorientation of insects with artificial light
Although it was the most accredited, however this theory was lacking in experimental confirmations because of the difficulty in monitoring the flight of insects with precision. This until an international group of researchers succeeded, thanks to the use of sophisticated stereoscopic cameras high resolution, to precisely track the flight trajectory of the night moths in the laboratory. Their research, published on Nature In 2024, he confirmed that the flight of these insects it is not directed towards the light source, but it revolves around us: from the examination of the trajectories it appears that the moths they turn the back towards the light source reference when they fly.
In the presence of an artificial light like a light bulb, they were observed Three types of flight:
- to “orbit”: the insect runs in a circle tight under the light source;
- “Stall”: the insect ascends rapidly with the back facing the light and then falls down;
- A “inversion”: when the light comes from below, the insect turns upside down and ends up on the ground.
When the researchers “simulated” the angle of natural light with artificial sources (for example by illuminating a white sheet from above), the insects have returned to fly regularly.
Even if the precise mechanism with which insects manage to interpret the angle of origin of the light is not yet confirmed, this study confirms that They are not attracted to artificial light, but that this, rather, induces them in confusion. The shape of the lamps, their arrangement in space and proximity to other superimposed light sources, do only complicate the situation further, and the insects end up flying in chaotic waysometimes slamming against them, giving us the wrong impression that are attracted to the light itself.
The effects of light on different types of night insects
This phenomenon is very pronounced for the ultraviolet and blue light, Towards which many wlehe and flies are particularly sensitive. Attention, not all night insects are influenced in the same way by the light: most of the mosquito species, for example, do not orient themselves with light to look for who to punish but is based on body heat, carbon dioxide and our smells. That’s why the mosquitoes also find us very well in the dark, and That’s why the “zapper” lamps sold just as an anti -media expedient, they don’t work With them and they only end up frying other unravelable night insects.
Other species of insects may be influenced by light for reasons not related to orientation: the firefield use their natural bioluminescence during the courtship And for this reason they could end up being attracted to artificial lights. Also ephemeral and dragonflydespite being daytime insects, they are sometimes attracted to night light, but it is not yet clear if certain sources of polarized light for the reflection of a pond or a watercourse or, in the case of dragonflies, if they use the area around a lamp, wedge of confused insects, like a rich hunting ground.
Other hypotheses on the attraction of insects towards light
There are other possible explanations on the behavior of attraction of night insects towards light, proposed by scientists in the 50-60s, but contrary to the theory of the bright “compass”, they do not have many experimental evidences in their favor.
One of these is that insects interpret the light as a “escape“: To avoid being trapped inside bushes, the insects would prefer areas from which the light comes, an open window between the foliage through which they can escape. However this hypothesis does not reflect the observed behavior of insects at all, who do not fly to the light, but they turn around us.
Another explanation is that night insects are not attracted to light itself, but from heat that generates. Although many insects, both night and daytime, are attracted to heat sources for metabolism reasons, this explanation is not entirely satisfactory: night insects have also been observed to fly also around “cold” artificial lights, the temperature of which was no longer warmer than the surrounding environment.
