Why Do Spiders Have 8 Eyes?
WouterThe number of eyes that spiders have is a very important factor. They need a way to track motion and detect danger. Having eight eyes can give them this advantage. However, a spider cannot see all eight at once. In order to be effective, all of their eyes have to work together.
There are two types of spider eyes: primary and secondary. Secondary eyes are the smaller ones that are usually immobile and can be found on the sides or on top of the head.
These small, oval-shaped eyes can help the spider sense movement and detect motion. Aside from providing better night vision, secondary eyes also enhance the spider’s ability to catch and defend against predators.
Spiders use their secondary eyes to detect polarized light. This light tells them where they are in relation to the sun. When illuminated, the eye reflects the light back through the retina, giving them a clear, silvery image.
Spiders also have primary eyes, which are used to view images. The main eyes are located in the cephalothorax, or the front of the head. Primary eyes can detect motion, but are not as good as human eyes. Generally, they are used for hunting.
Spiders also have a series of other eyes that are used for different purposes. Some species have fewer eyes. Others have four, six, or eight. Some of these spiders are hunters, while others are web-casters.
The arrangement of spider eyes can be useful for arachnologists in identifying species. Most spiders have eight eyes.
