A41 Artificial light interference

Topic

The nocturnal insect that flies guided by light finds, in artificial nocturnal light, a profound disturbance of its behavior: while this insect evolved using natural light sources as a reference to orient itself, artificial nocturnal light directly interferes with that reference on which it depends to navigate.

The photoreceptors of the nocturnal insect are adapted to function in the dark, with a very high sensitivity that allows them to capture the limited natural light available at night; But that same high sensitivity means that, when receiving artificial light much more intense than the natural light for which they are calibrated, the insect's photoreceptors become saturated or strongly desensitized.

This saturation of the photoreceptors of the nocturnal insect follows the behavior described by Michaelis-Menten kinetics: as the irradiance of the received light increases, the photoreceptor response grows less and less, until, above a saturation irradiance threshold, the photoreceptor stops being able to distinguish any additional difference in intensity, no matter how much the light continues to increase.

Beyond this sensory saturation, the nocturnal insect typically navigates with a very specific mechanism: it maintains a natural light source, typically the moon or stars, at a constant angle within its visual field, and adjusts its flight to maintain that constant angle as it moves forward. This constant-angle navigation mechanism works well with a natural light source, because that source is so far away that its angle barely changes no matter how far the insect moves.

When a nearby artificial light source replaces the natural light source, or is added to it within the insect's visual field, the same mechanism that normally orients it well begins to fail: as the artificial source is much closer than the moon or stars, its angle with respect to the insect changes rapidly as the insect moves, and the insect, trying to keep that angle constant as it always has, ends up generating an orientation error that forces it to fly in increasingly tighter spirals towards the artificial source itself.

Beyond directly attracting the nocturnal insect to the artificial source, artificial night light also reduces the visual contrast with which the insect perceives its environment at night, and this loss of contrast prevents it from detecting both the silhouettes of predators that could attack it and the spots on the flowers that normally guide its search for food. Thus, the same artificial night light that first saturates the insect's photoreceptors and then diverts it from its natural course also ends up leaving it exposed and unable to feed properly.

ID:2558