Flying insects often gather around artificial light sources at night, a behavior that involves insect navigation, physiology, and the disruptive presence of human-made illumination. This article explores the scientific reasons behind this attraction, identifies the types of insects involved, examines their light preferences, and discusses how this understanding is applied in insect control.
The Science of Light Attraction
The scientific principle explaining why many insects move towards light is called phototaxis, where an organism exhibits positive phototaxis by moving towards a light source. For many nocturnal flying insects, light plays a fundamental role in their natural navigation. Historically, these insects relied on distant celestial bodies like the moon and stars, which are fixed points of light, to maintain a straight flight path through transverse orientation.
In transverse orientation, an insect maintains a constant angle between its body and a distant light source like the moon. Since the moon is far away, its light rays are parallel, allowing the insect to fly in a straight line. However, when an insect encounters a much closer artificial light source, the light rays radiate outwards. As the insect attempts to maintain a fixed angle, it inadvertently curves its flight path, leading to a spiraling motion that brings it closer to the bulb.
Recent research suggests insects are not necessarily attracted to artificial light but become disoriented, mistaking it for the direction of “up” or the open sky. This “dorsal light response” causes them to tilt their backs towards the brightest point, leading to erratic flight patterns and trapping them in looping turns around the light.
Insects Drawn to Light
Many flying insects exhibit positive phototaxis and are commonly observed around artificial lights. These species are often nocturnal or crepuscular, active during the night or twilight hours. Common examples include moths, various types of flies, midges, gnats, and mosquitoes.
Beetles, including ground beetles and leafhoppers, are frequently found near light sources. Other insects showing this behavior include caddisflies, mayflies, and some species of wasps and bees. While some insects are drawn to heat from older light sources, the main attraction for many is the light itself, particularly for those using light for navigation.
Light Preferences and Aversions
Not all light is equally attractive to insects; some wavelengths are more appealing. Many insects, unlike humans, perceive ultraviolet (UV) light, which is highly attractive to a wide range of species. Insects often have photoreceptors sensitive to UV, blue, and green light, with their vision spanning wavelengths from approximately 300 to 650 nanometers.
UV light is a strong attractant because it mimics natural light cues for navigation, such as sunlight or moonlight, and is associated with food sources like flowers that reflect UV patterns. Blue and green light are also attractive to insects due to their visibility within the insect visual spectrum. In contrast, warmer colors like yellow, orange, and red are less attractive to most insects.
These colors have longer wavelengths and lower energy, making them less detectable or invisible to many insect species whose visual range does not extend into these warmer hues. While some insects, like cockroaches and certain beetles, exhibit negative phototaxis by moving away from light, this is often a survival strategy to avoid predators or unsuitable environments.
Leveraging Light for Insect Control
Understanding insect phototaxis allows for targeted pest control strategies. Insect light traps, commonly known as bug zappers, exploit the strong attraction of many insects to UV light. These devices contain a UV fluorescent lamp that lures insects towards an electrified grid, where they are electrocuted. Bug zappers are effective against insects with strong positive phototaxis, such as moths and certain flies.
Another practical application involves using light to deter insects from specific areas. Yellow “bug lights” are a common example; they attract significantly fewer insects compared to white or blue lights. This is because yellow light falls outside the optimal visual range for many insects, making it less visible and less enticing. Choosing light sources with wavelengths less perceptible to pest insects can reduce bug concentration around outdoor living spaces.