Spiders have an extensive visual system. Their eyes are complex and can detect polarized light and motion. In addition to their visual system, spiders also have specialized senses. Some spiders have very good night vision and are able to spot predators.
There are two main types of eyes in spiders. The first type is called the “primary” eye. These are fixed, and are used to detect prey. They can only shift their lenses very slightly. However, they have excellent night vision and can detect polarized light.
The other type of eye is called the “secondary” eye. This type of eye can enhance spider vision. It is smaller than the primary eye, and can be oval, round or semilunar. Usually, it has a tapetum lucidum, which reflects light back through the retina.
Most spiders have eight eyes. There are some species that have fewer, or even none. One of the most common groups of spiders has only six eyes. Others have as many as 12.
Spiders need a certain number of eyes to perform different tasks. For instance, jumping spiders need to be able to actively hunt. Those with fewer eyes can still catch prey, but may have a hard time recognizing their surroundings.
Jumping spiders are active hunters. Their front pair of eyes is great for identifying detail, while their side pairs are important for warning them of potential danger. Having a good number of eyes also helps spiders detect movement.