The visible light spectrum for humans is made up of seven different colors: red, orange, yellow, green, blue, indigo, and violet, in length from 400 to 700 billionths of a meter in length.
Insects see things different to humans. The human eyes distinguish colors in only a small part of the solar spectrum that we call visible. We distinguish colors because our vision is trichromatic. Different animals perceive colors differently due to variations in spectral sensitivity. Most insects also have trichromatic vision like us but with color sensitivities shifted to the ultraviolet range (Ashfaq et al, 2005). They are attracted to blue and ultraviolet wavelengths because they are shorter with a higher frequency while red wavelengths are longer and have a lower frequency. The latter is much harder for the insects to detect (Luettich, 2003; Pate J and A Curtis, 2001). So the spectrum of colors visible to insects is a little higher in frequency than what we humans can see
In short, light becomes visible to insects around the ultraviolet part of the color spectrum and ends at yellow light and that’s why many insects do not see red. This makes colors in the red spectrum a suitable choice for use in anti-insect gear.
Summaries of important related scientific articles are listed below.
This experiment was conducted in the area of Punjab Agriculture Research Station (PARS) and Chak No.33 JB Faisalabad to evaluate the response insects to varying wavelengths of light. During experiment, lights of six different colors (blue, green, yellow, red, black and white) were tested. All lights were arranged in a line on agriculture land, close to Faisalabad Airport. Tree rows/blocks, forest nursery, fruit garden, wheat, maize and fodder crops were the main vegetative covers in the vicinity. Each selected color light was properly projected on 1m2 vertical screen (made of white cotton fabric) placed one meter high above the ground. All lights were kept on simultaneously for half an hour and the insects attracted on both sides of the screens were collected in tubs containing soapy water. At the end of experiment, the collection was shifted to properly labeled storage bottles for counting and identification into respective orders. The highest number of insects was observed in container placed under black light (ultraviolet light), while the lowest in that of red light. Similarly, the common insect orders frequented among all color lights were Diptera, Coleoptera and Lepidoptera respectively. The experimental results indicated that insects are attracted in more number on lights with short wavelengths and high frequencies and vice a versa.
Luettich K. Field Biology and Ecology. University of North Carolina at Charlotte, Summer Ventures in Science and Mathematics. July 19, 2003, pp 1-8.
The purpose of this study is to determine the relationship between the differential responses of insects to the different wavelengths of light. Out of the seven different light wavelengths, three were used. A total of twelve different orders were attracted to the light. Through the Chi-square tests it was found that there was a difference between the insect orders and their attraction to light wavelengths. Overall the blue and ultraviolet wavelengths attracted the most insects in each of the twenty-minute periods. Red light attracted the lowest number of insects.
Insect response to different wavelengths of light in New River State Park, Ashe County, North Carolina
Pate J and A Curtis. Field Biology and Ecology. University of North Carolina at Charlotte, Summer Ventures in Science and Mathematics. July 13, 2001, pp 1-8.
The purpose of an experiment performed in Ashe County, North Carolina was to find out how different insects respond to varying wavelengths of light. We used six colors of light: blue, green, yellow, red, ultraviolet (“black”) and white. The lights were arranged in a circular pattern in a parking lot and set on top of soapy trays of water. The lights were on for half an hour. The insects were counted and classified according to their order. The lowest number of insects was in the red light container and the highest number was in the ultraviolet light container. Also, the most common order of insect found among all the colors of light was Trichoptera. The results of the experiment indicated that insects are more attracted to lights with short wavelengths and high frequencies.