Flies perceive the world in a way that differs significantly from human vision, making certain colors more appealing or repelling to them. Understanding these distinctions is useful for various applications, including pest management. Their visual system processes light and color cues that guide their behavior, from finding food sources to locating mates and breeding sites.
Colors That Attract Flies
Flies are attracted to a range of colors, often those associated with food, decaying matter, or warmth. Blue light, particularly in the ultraviolet (UV) spectrum, is a significant attractant for many fly species, including house flies. Blue traps can attract a substantially higher number of flies compared to neutral gray controls. This strong attraction to blue is thought to stem from flies perceiving visual contrast differently than humans, where blue light balances UV wavelengths and shadow, making it highly stimulating to their compound eyes.
Beyond blue, yellow is another color known to attract various flying insects, including some flies like fruit flies. Yellow can mimic the color of plants under stress, flowers, or ripe fruit, which are appealing as food sources or breeding grounds. Some studies suggest that yellow may attract certain flies because of its association with decaying organic matter. Orange can also be attractive, as fruit flies are drawn to the scent of citrus, which is often orange in color. Additionally, dark colors, like black, can attract flies, especially in outdoor settings, as these surfaces absorb heat and create shadow contrasts that may resemble shelter or food cues.
UV light, though invisible to the human eye, is a strong attractant because it mimics the natural reflective properties of flowers, fruits, and organic matter they feed on or use for laying eggs. Specific UV wavelengths between 350 and 370 nanometers are particularly appealing, triggering a strong attraction to the light source. This phototactic response is why UV lights are widely used in fly control devices.
Colors That Repel Flies
Certain colors are less appealing to flies and may even repel them. White is generally considered a color that flies tend to avoid or are less attracted to. This may be because white reflects all light, offering little contrast or cues that would signify food or shelter. Similarly, some shades of green can be less attractive to flies, as they might blend into foliage and not signal potential food sources or breeding sites.
Warm tones like yellow and orange have been observed to repel some fly species, even though yellow can also be attractive to others. This effect often depends on the specific fly species and context. For instance, while some fruit flies are drawn to yellow, other types of flies might avoid it. Light gray shades, such as soft dove gray, are also known to deter insects like mosquitoes and flies, as these colors reflect light well and are less attractive.
The Science of Fly Vision
The way flies perceive color is fundamentally different from humans due to their unique visual anatomy. Flies possess compound eyes, made up of thousands of individual visual units called ommatidia. Each ommatidium acts like a miniature eye, containing photoreceptor cells that capture light independently. The fly’s brain then processes these inputs from multiple ommatidia to form a mosaic-like image of the world.
This compound eye structure gives flies a very wide field of view, almost 360 degrees, allowing them to detect movement from nearly any direction. While their resolution is generally poorer than human vision, their ability to detect rapid changes in light intensity, known as flicker fusion frequency, is much higher, enabling them to react quickly to movement. Unlike humans, whose vision relies on red, green, and blue cones, flies perceive a broader spectrum of light, including ultraviolet (UV) light. They are highly sensitive to UV wavelengths, which play a significant role in their navigation, foraging, and mating behaviors. However, flies are typically blind to the color red.
The specific distribution of screening pigments within each ommatidium allows different fly species to perceive distinct permutations of color. Flies navigate a visually complex environment.
Practical Applications
Understanding how flies perceive color has significant practical applications, particularly in pest control. The strong attraction of many flies to blue and UV light has led to the development of effective fly traps that use these wavelengths as lures. UV light traps, often combined with adhesive surfaces or electric grids, are widely used in homes, schools, offices, and food handling areas to attract and capture flies. Some modern traps utilize blue LED lights, which are particularly effective due to their high output in the blue spectrum.
In agriculture and other outdoor settings, knowledge of fly color preferences can inform pest management strategies. For example, using blue-colored devices has proven more effective than traditional yellow traps for some fly species. For personal use, choosing certain clothing colors can help reduce fly annoyance. Flies are generally more attracted to dark colors like black and navy blue, and less attracted to light-colored clothing, especially white. This is partly because they use heat receptors to locate warm bodies, which dark colors tend to absorb. Therefore, wearing lighter colors might help deter them when outdoors.