Ricky Howard, age 12, of Spokane, Washington, for his question:
Do insects really have more than two eyes?
We cannot judge the insects by our way of doing things. For example, some have ears in their legs or abdomens. They sense smells, touch and possibly taste with their antennas. A few have no eyes at all. When young, some insects have a dozen or so simple eyes. Some adult insects have two eyes but many of them have five.
Many adult insects have the same sort of vision as the bee. She has two large compound eyes and three small simple eyes called ocelli. The two compound eyes are those big bulges, one on each side of her head. She cannot turn her head to look around. But her domed eyes can see the scenery on all sides, also front and back. We know, more or less how they work. But we know less about the three small ocelli, set in a triangle on her forehead.
When an insect's compound eye is greatly magnified, it looks like a dome set with honeycomb cells, all neatly fitted together. Each cell is a tiny lens that captures a picture of the scenery. It has a tiny retina screen and a tiny nerve to relay information to the insect's brain. A clear picture depends on the number of lens in these compound eyes.
Certain worker ants have only six compound lens. Each catches a glimpse of the scenery from a slightly different direction. But the total effect must be very dim and blurry. The house fly has 4,000 lens in each compound eye. Together they form a picture that must look like a neat mosaic of six sided sections. She gets a clear view from all directions which makes her so hard to swat. The dragonfly has even sharper vision for each of her bulging compound eyes is fitted with about 30,000 little lenses.
These compound eyes are able to detect the slightest movement in the scenery. This is important because an insect needs to know when to flit from a possible foe. However, compound eyes cannot be focused on objects near and far. They catch a good picture of the scenery only up to a few feet.
Some, but not all, insects have three ocelli on the forehead. These organs are called simple eyes, though nobody is quite sure how they help the vision, if at all. Researchers have covered a bee's compound eyes to see what happens. The remaining ocelli do not seem to help, for she acts as if she is blind.
When only the ocelli are covered, a bee can see but not quite so well. It takes her a little longer to notice changes in the light. For this reason, it is thought that perhaps the three little extra eyes help the compound eyes to sense brightness and perhaps give sharper pictures.
Many insects have color vision, though there is no way to know whether a yellow flower looks the same as it does to us. In their own way, they can detect blues and violets, yellows and greens. But apparently they see red as black, or colorless. And some insects can see colors in the ultraviolet range which we cannot see. However, humans see 100 times better than a sharp sighted fly.