Why are they flying into the light?

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agki, 29.05.2007 19:50

I remember when I was a small schoolboy, a street lamp with a working light bulb was the only way to see many insects. On warm nights after dusk, by 11-12 o'clock, a lot of things just flew in: there was no point in mentioning butterflies, there were a great many of them, but the lit walls were literally covered with cicadas, mosquitoes, winged individuals of small black ants, caddis flies, freckles, golden eyes, mayflies, sometimes ant lions, sometimes in a general whirlwind, otherwise you can not say, there were small fillies, in rainy weather all sorts of water lovers and water beetles were added, gladyshi like, the last one was remembered - that moths like to circle the light, it is well known, and that different straight-winged and water insects can circle with them, in my childhood was a discovery for me. It was absolutely incomprehensible what the insects, who spend most of their lives in the water, were doing here, and why the light makes earwigs and bears fly up, which hide in darker places during the day. If, for example, ground beetles are shown under a street lamp with a clearly gastronomic interest, then why do mantises come to the light - also to have dinner? Does anyone know any versions on this?

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01.06.2007 11:05, Sungaya

"....Light can attract more than just insects. For example, birds in large numbers sometimes fly during their seasonal migrations to the light of lighthouses. Saury fish are caught in nets, attracting them there with the help of powerful light sources. Therefore, this is a general biological phenomenon.

Representatives of almost all orders of insects with a wide variety of lifestyles fly to the light. These are mostly insects that are active at dusk and at night, but sometimes typical diurnal forms also appear at the light source. The arrival of daytime insects at night is explained by the fact that they stayed at the light source in the evening or someone disturbed them. In principle, the time to light is not limited only to night time. Many small daytime insects fly to the light of a UV-emitting lamp . Therefore, insects, if they are active, react equally to an artificial light source, regardless of their lifestyle.

An explanation of the summer of insects into the world should take into account the following facts::
1) insects with a very diverse ecology are exposed to light;
2) the insect's flight path near the light source is usually a complex broken curve;
3) near the light source, the insect's coordination of movements is often disrupted and it sometimes falls to the ground;
4) the insect is attracted not only by a point light source, but also by an illuminated screen
5) insects do not fly towards the Moon or the Sun, although it is possible for insects to fly towards dawn;
6) UV radiation is particularly attractive for some insects;
7) the insect may leave the illuminated area after some time after arriving at the lamp;

There are a number of hypotheses that explain the years of light.

Zh. Loeb (1924). Draws attention to the relationship between the tone of the limbs and the flow of light falling on the eyes. Experiments have shown that lighting the left eye increases muscle tone on the right side and vice versa. Accordingly, an increase in tone leads to a more energetic work of the muscles from the unlit side, as a result of which the insect turns to the light.

However, the Lebesgue mechanism is not sufficient to explain the attraction of insects by light. It does not allow us to understand why an insect that has flown to a light source can then leave the illuminated area, nor the special attraction of UV radiation, the sensitivity of the insect's eye to which is not so high, nor why insects flying in nature at different angles to the rays of the Sun and Moon do not turn to them as they should would be by Loeb's hypothesis.

V. Buddenbroke (1917). It is known that in insects it is possible to observe menotaxis, i.e. movement at a certain angle to the light rays (this is easy for insects to do, keeping the image of the light source in a certain omatidia of the eye or in their group). It is obvious that if an insect moves while being guided by the rays of the Sun or Moon, which can be considered parallel to each other, then its course is a straight line. However, if you try to maintain a constant angle with respect to radially divergent light rays, its course turns into a logarithmic spiral (and the appearance of random deviations and turns does not change the final result).

From this point of view, it is difficult to explain the attraction of insects not by a point source, but by a large illuminated screen, why an insect that has arrived can then fly away from the light, as well as the special attractiveness of UV radiation. In addition, menotactic orientation to the rays of the Sun and Moon occurs only in special cases. Usually in nature, insects use a variety of ground landmarks, survey objects that attract them, and their course is a complex and rather erratic curve.

G. A. Masokhin-Porshnyakov (1960). Light is the most versatile and reliable indicator of an open space. Here, a special role is played by UV radiation, which is practically not reflected by land objects, with the exception of the water surface. Indeed, day or night insects that have accidentally flown into the room beat against the window panes, trying to get out of the confined space. At night, on a lighted screen, insects behave in a similar way. When an insect gets caught in a beam of light at night, it perceives the surrounding darkness as a closed space and, trying to escape, flies towards the light.

From this point of view, however, it is difficult to explain how an insect that has already flown to the lamp can fly away from it again, why there are no similar behavioral disorders under the influence of moonlight. In addition, not all individuals of the same species, getting into the illuminated space, somehow change their behavior.

It is most likely that the flight of insects into the light is a complex multi-stage phenomenon, and at each stage there are different mechanisms.

The first stage. It is obvious that insects in search of favorable light conditions are guided by the gradient of light. For an insect coming out of hiding , the light is a reliable indicator of entering the open space. After entering an area with favorable light conditions, the insect feeds, looks for a sexual partner, a place to lay eggs, etc. However, if it migrates, it is more economical for it to follow a straight course, which is easy to maintain in the way mentioned above (while maintaining the angle to the light rays). A migrating insect may choose an artificial light source as a reference point . Then it must inevitably approach it, and at a sufficient distance from the lamp, its course will be relatively close to a straight line and will begin to bend sharply only when approaching the lamp (Buddenbroke's hypothesis). Both the sun and the night sky are sources of UV radiation, so it is most likely that a source that emits ultraviolet light will be chosen as a reference point.

The second stage begins when the insect approaches the light source at a distance of 30-10 m. If an insect uses a natural light source (Sun, Moon) as a reference point, then when moving in its direction, its intensity does not change. When moving to an artificial light source, the illumination increases dramatically (especially at a close distance from the lamp). The sharply increasing intensity of light literally blinds the insect (orientation and coordination of movements are disrupted, sometimes due to a nervous shock, the insect falls to the ground). However, the insect continues to strive for light for the following reason. When fleeing from any irritating influence, insects use light as an indicator of access to open space. However, in this case, the closer the insect is to the light, the greater the irritating effect of the latter. It is possible that turning away from the lamp for an approaching insect is difficult because the anterior ommatidia of the eye begin to adapt to the light earlier. Then what is behind will be perceived as a closed space and will increase the movement of the insect towards the light.

In principle, such a reaction can also be observed when an insect unexpectedly enters bright sunlight. However, for sunlight within the Earth's limits, the amount of illumination does not change when "approaching" the Sun. Therefore, an insect moving in bright sunlight does not have such a reaction, since its eyes quickly adapt to the light. It is possible that the Lebowski movement mechanism is implemented in the vicinity of the lamp.

The third stage. This stage begins if the insect has come almost close to the lamp and has not burned down or died for any other reason. While it is beating around the lamp, trying to get out into the "open space", its eyes gradually adapt to the light and the general excitement subsides. Often, the nocturnal insect perceives artificial lighting as the onset of day and takes a pose near it that is characteristic of daytime rest or even flies away.

References: V. B. Chernyshev (Department of Entomology) "Ecology of insects", MSU Publishing House, 1996 ... "

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