Why Spiders Have 8 Eyes
WouterUnlike humans, spiders have eight eyes. These are arranged in two rows. The first row contains the primary eyes. The second row consists of the secondary eyes. This eye arrangement varies depending on the species.
Primary eyes serve a number of purposes. They help spiders detect danger and track prey. Some spiders use their main eyes to look at a wide range of details. Others rely on other senses to help them locate their prey.
Secondary eyes are specialized to perform a specific task. Often, they are small and round. When turned toward a light source, they may appear silvery or shiny. Most of these eyes have a tapetum lucidum which reflects light back through the retina.
Secondary eyes are important to spiders. They enhance their ability to detect movement, especially in the dark. Spiders are capable of seeing polarized light. This tells them where to focus in relation to the sun.
Although spiders have eight eyes, not all of them are used for the same functions. The principal eyes are the most important. Two of them, located at the front of the head, are responsible for providing spiders with a stereoscopic view. Combined with the other eyes, they form an “X” pattern of high-resolution color vision.
Secondary eyes can also provide spiders with better night vision. However, many spiders do not have good vision. As a result, they have to rely on other senses, such as vibrations picked up through their hairs, to find their prey.
