Spiders are animals with unusual appearance. To someone they seem frightening, others on the contrary, love them and even contain houses. What you will not refuse to them, so it singularity. Even the number of eyes at a spider differs from that at the majority of animals.
Pairs of eyes of a spider
The spider can have a different number of eyes depending on a look to which it belongs. Their quantity is capable to vary from two to twelve. Some arthropods do without organs of vision at all. For example, cave spiders, all the life carrying out in the dark, do not possess eyes as they are simply not necessary to them.
Though at the majority of spiders eight eyes located in two ranks are available the sight plays a major role in life of these animals not, and, despite such number of visual bodies, they see poorly. The spider able to make out a subject at distance of thirty centimeters can already be considered as sharp-sighted. However the vast majority of spiders also does not need good sight. They spin a web where wait the production.
That the mosquito or a fly were caught in their net these arthropods recognize by vibration of a web which is created by the fluttering victim.
Structure of eyes of a spider
Numerous organs of vision of a spider work not equally. The middle pair of eyes usually has the big sizes, than additional eyes. Principal organs of sight are deprived of pocket mirrors which reflect sunlight, but bunches of muscles thanks to which eyes can move are attached to them. Side bodies, on the contrary, are supplied with pocket mirrors, but deprived of muscular bunches.
Most likely, it is caused by the fact that eyes perform different functions: lobbies at the hunting types monitor production, and side – watch approach of danger.
Eagles among spiders
There is, however, a group of spiders who have extremely acute eyesight. These are vagrant spiders racers who do not sit in place, waiting the production, and actively are engaged in its search. The sight of these representatives of arthropods on sharpness is comparable with sight of the person. Besides, they are capable to distinguish colors that is not characteristic of so primitive animals. At racers eye muscles are perfectly developed that allows this animals to monitor production, and the main eyes are supplied with a large crystalline lens and a little extended in length like the telescope. Side eyes allow a vagrant spider to fix the movement sideways, behind themselves and over themselves. In spite of the fact that an eye at this spider eight, and they possess different functions and show the different picture, together they act as the harmonious visual device providing survival to this small animals.