Although the main focus of this blog is human vision, from time to time we take a look at how other creatures see the world. A while back we examined the amazing eyes of several sea creatures and in another post we discussed the anatomy of eagles’ eyes. So, in that tradition, I thought in this post we’d take a look at the eye of the common housefly.
One of the most compelling facts I turned up in my research is that flies’ brains are very highly evolved for processing visual information. Pest-management experts estimate that about 70 percent of a fly’s brainpower is devoted to seeing. That makes the fly essentially an airborne eye—a very cool way to think of these pesky little creatures.
Flies have “compound eyes” a term that describes eyes that comprise thousands of light-capturing structures called ommatidia. An adult housefly has about 3,000 ommatidia in each eye—the hexagonal patterns we see in close-ups of fly eyes are the outermost section of these structures. Compound eyes are particularly handy for seeing things up close, and things that are moving—attributes very important to flies and their insect brethren.
Each of the thousands of ommatidia in a fly’s eye has sensory cells that contain a photopigment that responds to specific light wavelengths. The structure ensures, as one source puts it, that “…light from any point is collected by six different ommatidia, and therefore the intensity of the image on the retina is greatly enhanced. This makes the vision of the flies much more sophisticated than that of almost any other insect.”
Of course, all flies do not see the world the same way; as one expert says, “Each fly species has different visual sensitivity that changes according to the sex of the fly, its age, its feeding status, its reproductive stage, etc.”
We’ve only just scratched the surface of a topic that I am sure is the subject of many doctoral dissertations and perhaps even entire careers, but I’ve hoped it’s help you understand why it’s so hard to swat a fly—it’s those amazing eyes that allow them to always see you coming!
