Dear Kathryn,
Most spiders have quite a few eyes, but they usually can’t see very well. Then again, seeing isn’t everything.
That’s what I found out when I went to visit my friend Rich Zack, a scientist at Washington State University who knows a lot about insects and spiders.
Zack explained that spiders have a number of small lenses on the top of their heads. These simple lenses let them see changes in light and dark. It’s probably a pretty blurry view, he said.
There are more than 40,000 spider species on Earth. We can often identify a spider by counting its eyes and seeing how they are arranged.
A wolf spider, for example, has three rows of eyes to help it hunt in the dark. The first row has four small eyes, the second has two large ones, and the third has two medium-sized ones.
A jumping spider has two huge eyes and two small ones on the front of its face. On top are two tiny eyes and two medium eyes. This way, it can see all around.
Some scientists are curious about how different spider eyes work. For example, the size and location of some eyes appear to help spiders see more details. Others help them see a wider view of the world, even if it’s fuzzy.
A few years ago, scientists discovered a kind of spider that lived in dark caves. It didn’t have eyes, but it didn’t really need them either.
In fact, most spiders live in the dark. We see some scurrying around during the day, but most are nocturnal, which means they move around at night.
If you pointed a flashlight in the direction of a wolf spider, you could see its eyes shining in the dark. They have iridescent layers called tapeta. Cats and other animals who have evolved to look for food at night also have tapeta to help them see better in the dark.
With or without eyes, spiders are pretty good at using their other senses to survive, too.
“Most spiders rely on smell or touch to capture prey and perceive their environments,” Zack said. “Some spiders can feel the vibrations on their webs, then move out to see if that vibration was caused by a potential item of food.”
Finding food is one big responsibility for spiders. Finding a mate is another. Jumping spiders use their bright colors to attract one.
A group of scientists thought that if these brightly colored spiders were attracting mates, then maybe the spiders saw colors, too. They found out from their experiments that some jumping spiders have special filters in their eyes to help them see certain colors.
So, even though spiders may not have the best eyesight, they view the world in all kinds of ways. Some can see near, some can see far, some see color, and some don’t see at all.
Sincerely,
Dr. Universe