Updated: Jan 27, 2022
Despite the constant innovation of the modern world, one thing's for certain―you can’t invent a new color. Humans are only able to see the rainbow of colors that we know to exist, known as the visible light spectrum, caused by the signal that our red, blue, and green cones send to our brain when our eyes point at a colored object. These colors have wavelengths ranging from about 400-800 nanometers, allowing us to see purple, red, and everything in between. Now, what if I were to tell you that a housefly, generally ranging from a miniscule 6 to 7 millimeters in length, can see colors that you can’t?
The term “bug eyes” isn’t spoken without reason. A typical insect can see colors with wavelengths ranging from 300-650 nanometers. This means that although they cannot see the red-orange-yellow section of the human visible light spectrum, they are able to see ultraviolet rays. Consequently, instead of having blue, green, and red cones like humans, insects have blue, green, and ultraviolet cones. Ultraviolet light is invisible to the human eye since its wavelength covers the range of 100-400 nanometers in the electromagnetic spectrum―however, flies can detect this light. Specifically, they can see UVA rays, which are 315-400 nanometers, and partially see UVB rays, at 280-315 nanometer. The sun’s rays naturally emit UVA, UVB, and UVC rays, though UVA rays make up 95% of the rays that beam onto the Earth.
Not only can house flies see unique colors unknown to humans, but they can clearly identify them with fine resolution. Due to their compound eyes, with thousands of lens-capped “eye-units,” it has long been believed that insects can only see pixelated and low-resolution images. Compared to the single lens present in human eyes that allows for sharp focus, scientists previously assumed that the compound eyes of insects were much less capable of capturing high-resolution images.
It was not until recently that researchers from the University of Sheffield’s Department of Biomedical Science proved the previous assumption wrong. They discovered that the unique composition of insect eyes can capture clear images. This ability is derived from the ways in which the photoreceptor cells in insect eyes react to image motion. Although the thousands of “eye-units” cannot move in and out of focus to accommodate images like humans do, the photoreceptor cells inside of their compound eyes can. This allows the housefly to sample an image of the world with a fairly high resolution.
A tiny housefly is far more sophisticated than we may assume. Despite the fact that their brains are the size of our freckles, they can see colors that we cannot begin to comprehend.
 Lucas, Jim. "What Is Ultraviolet Light?" Livescience, Future US Inc, 16 Sept. 2017, www.livescience.com/50326-what-is-ultraviolet-light.html.
 Turpin, Tom. "Insects See the Light." Agricultural Sciences Education and Communication, Purdue, June 2012, www.asec.purdue.edu/natural_resources/4-H,NR,Projects/Projects/entomology/TurpinArticles/Insects%20See%20the%20Light.pdf.
 University of Sheffield. "News Archive." The University of Sheffield, 5 Sept. 2017, www.sheffield.ac.uk/news/nr/insects-can-see-better-than-scientists-thought-1.727290.