Which Spiders Have 12 Eyes?
WouterThe number of eyes in spiders varies. Some genera have four, six or eight eyes, while others have none. There are also a few species that have twelve eyes.
In general, spiders have two types of eyes. They are called principal and secondary. The difference between the two is important to understanding the spider’s visual system. The principal eyes are located on the front of the head and are used for hunting prey. The secondary eyes are located on the sides or back of the head. They help the spider detect movement. They aid in locating prey, and they enhance the spider’s ability to defend itself.
The main function of the principal eye is to track an image. It also contains muscles to move the retina. This allows the spider to view ultraviolet light.
The secondary eye is a motion detector. It expands the range of the primary eyes. It has a tapetum lucidum, which reflects light. This helps the spider see better at night. The tapetum lucidum also shows a shine when illuminated. It may be oval, round, or semilunar. The size and sensitivity of the secondary eye vary from species to species. The position of the secondary eyes will determine how useful they are for the spider.
The arrangement of the eyes on the head is very helpful when identifying a family of spiders. Some groups show large displacements of up to 15 degrees. This indicates that major differences in retinal development exist.
