Spiders are not blind, as most of the spider species use their eyes to spot their prey. The number of eyes, however, varies depending on the spider species. For determining the family of a spider, the arrangement of its eyes is often considered.
Jumping spiders of the family Salticidae, flower spiders of Thomisidae, net-casting spiders of Deinopidae, and wolf spiders of Lycosidae are some of the groups of spiders that have good vision, which helps them in hunting prey and recognizing rivals and mates.
While most spiders have eight eyes, some can have six or fewer or none at all. Some of the common spiders with eight eyes include the jumping spiders and the huntsman spiders.
The front-eyes are typically used for identifying and hunting prey, while the side-eyes are employed for detecting motion, which is also crucial for its safety. Some spiders possess median eyes, which are used for detecting polarized light. During hunting, they use this ability for navigation.
The eyes of a spider do not move, which means it cannot shift its vision. Although the lenses inside its eyes can slightly shift, it does not give a complete view of its surroundings. It needs extra pairs of eyes for its safety.
Most spiders, being nocturnal hunters, move around in the dark. These nocturnal species, unlike the daylight hunting spiders, have poor vision. They are only able to see different light and dark shades, which helps them in wandering, web building, and feeling potential danger. These spiders mostly rely on their ability to sense web vibrations for finding their prey.
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