How many spider eyes are there

The number of spider eyes :

The number of eyes of spiders varies from one species to another, as most of them have eight eyes. A few have six eyes, four eyes, or one pair of eyes, and there are also spiders that do not have eyes at all, which are spiders that live in caves and dark places where light does not reach, so they do not need to see and hunt their prey based on their sense of smell, sense of movement and vibrations.

The spider known scientifically as (Sinopoda scurion) is the first hunter spider discovered in the world that lacks the presence of eyes, and a scientist found it at the Senckenberg Research Institute in Frankfurt in one of the caves of the Republic of Laos, and scientists point out that the decline in the eyesight of this spider is a kind of adaptation to living permanently in a cave that does not reach the light at all.

The reason why most spiders have multiple eyes :

Most spiders need to have many eyes around their head to be able to see the things around them, they do not have a neck, which means that they are unable to move their head to be able to see the things on the sides of the head as humans do, and spiders have different types of eyes, each with a different function; for example, the eyes that surround the head of spiders help them quickly locate prey to be able to catch it, the large central eyes help jumping spiders distinguish shapes, and the small side eyes help to monitor predators.

The structure of the eyes in spiders :

Primary eyes :

When examining spiders that have eight eyes, it can be seen that these eyes are arranged in two rows, a front row and a back row each containing four eyes, and the eight eyes are divided into primary eyes, which are the pair of eyes that are located in the middle of the front row, and secondary eyes, which are the remaining six eyes, and the primary eyes are characterized by containing light-sensitive pigments in the peripheral parts of them that are close to the lens of the eye, and the accuracy of vision in the primary eyes of spiders varies from one species to another, for example, the primary eyes of jumping spiders are characterized by their breadth and their ability to see with high accuracy in places with strong lighting as for the basic eyes of spiders, the Spinning the circular fabric and ground spiders enables them to see too, but with low resolution.

Secondary eyes :

The secondary eyes of spiders differ from the primary eyes in that the photosensitive pigment is in the inner part; that is, near the optic nerve, and the secondary eyes contain a transparent mat or a mirror-like choroidal mat located behind the retina that helps reflect light through photoreceptors, and the secondary eyes adapt to increase the amplitude of vision to see objects located in the lateral periphery of the spider, and they also help to monitor moving objects and determine directions depending on the sun or other celestial bodies.

Anterior lateral eyes :

The importance of the anterior lateral eyes of the spider appeared when the scientist Daniel Zorich and a number of other scientists from Macquarie University in Australia conducted a study on a type of jumping spider known scientifically as (Servaea vestita), with the aim of studying the role of one pair of eyes – the anterior lateral eyes – in the development of the visual system of spiders.to achieve this goal, the scientists covered the front Central eyes of the spider and the rear eyes. after that, the scientists showed the spider moving dots on a screen simulating the movement of flies; the Spider’s favorite food, and monitored the Spider’s reactions.

The experiment showed something amazing; the spider was able to detect, chase, and attack the target despite using one pair of eyes, and the scientists repeated the experiment 52 times using a different Spider each time, and these experiments proved that the pair of front side eyes – which had not previously received sufficient appreciation from scientists – may be the most superior element in the Spider’s visual system, which shows a clear development covering almost 360 degrees with a high degree of accuracy, the scientists concluded that the different eyes of the Spider share different visual tasks, such as: determining movement, analyzing the details surrounding the Spider accurately high.

Eye-brain connection :

Both the primary and secondary eyes connect to the Spider’s brain in different ways, allowing visual inputs from both types of eyes to pass to the brain through the visual processing centers located in the Spider’s head in order to process them, form an integrated image of the spider, and achieve an accurate and wide range of vision.

The mechanism of vision in spiders :

The scientist Elizabeth Jacob was able to obtain a grant at the University of Massachusetts at Amherst to develop a special device to track the eyes of jumping spiders specifically, and through this device, it is possible to accurately determine the location and movement of the eye while tracking the visual target and to know how the brain processes the information that arrives from the eye, and the work of this device can be likened to opening a window in the Spider’s brain to be able to track the mechanism of its work in examining complex images that arrive from the eye to obtain the specific information it is looking for only.

Scientist Elizabeth Jacob during her experiment found that spiders, like other living beings, are able to see a lot of things that surround them at a certain moment, but they need to classify the visual information they receive to focus on the information that interests them only as the presence of Prey, an enemy, or a potential mating partner, and spiders are able to achieve this thanks to the primary and secondary eyes specialized in detecting various information, as the six fairly simple secondary eyes equipped with a lens and a fixed retina are adapted to monitor any movement around the Spider.

As for the basic eyes, they are more complex; they consist of a fixed lens that is part of the external structure of the spider, and a retina inside the head at the end of the eye tube that contains a lot of photoreceptors that enable the spider to see objects with high accuracy, although its field of vision is narrow not exceeding ten degrees due to its small size, this obstacle can be overcome thanks to the muscles that control the eye tube that carries the retina, which enables the spider to direct the eye tube like the radiation of flashlights, then the visual information received by the Spider’s eyes is transmitted to the brain, which interprets these images and enables the spider to See what interests him.

Adaptation of the eyes of some species of spiders :

There are many types of spiders in the world, so they have very diverse visual systems, as the eight spider eyes show a large variation in eye size, position, and field of vision, depending on the lifestyle of the spider and the way it feeds, and some differences in the characteristics of the eyes in some species of spiders can be reviewed as follows:

Active hunting spiders: examples of them are hunting spiders (scientific name: Sparassidae), as this type of spider has large middle-sized eyes with two directions front and back that provide the necessary information to identify and track prey.

Spiders that build webs to catch their prey: such as long-jawed spiders, the tropical spinning spider, and spiders that lurk their prey such as crab spiders (scientific name: Thomisidae), as these types of spiders are characterized by smaller eyes distributed on the top of the Spider’s head so that they are separated by equal distances, and some reticular spiders also have eight eyes, including a pair of large-sized rear eyes called Searchlight eyes, where they have large forward-curved lenses that help to collect and focus the available light very efficiently, thanks to the light-sensitive membrane that is made inside the eye every night and is destroyed at dawn because it is not needed during the day, which helps the spider to monitor the prey and catch it with the net accurately during the night.

Wolf spider: most spiders belonging to the wolf spider type have reflective eyes; the four large rear eyes have a developed transparent mat that helps them monitor the movement of prey during the night, and when the lighting is dim.

Hunting prey by the multidirectional vision :

The jumping spider is able to detect and catch its prey using three different sets of eyes according to the following steps:

  • The spider uses the lateral eyes to create a wide-angle but blurred image of the prey far from him and monitors its movement.
  • The Spider changes its direction to face the prey, and uses the large front eyes located in the center of its head to create a close-up and focused image of the prey – it may be colored-and the spider is able to chase the insect without losing its image thanks to the muscles that are able to rotate the eye capsule internally so that the retina of each eye remains fixed on the prey.
  • The Spider hunts its prey using the lateral front eyes to judge how close it is to the prey, and when it gets 2 to 3 cm away from it, it jumps on it with a short tight jump and grabs it.

Classification of spiders and their types :

Spiders belong to the arachnids or arachnids that belong to the largest division of animals, the arthropod division, and it is worth noting that spiders are not insects as some think, but are animals that feed on insects and play an important role in regulating the numbers of insects on the surface of the Earth. arachnids are also characterized by having an exoskeleton, eight legs, simple eyes, and strong jaws that enable them to tear their prey.

Scientists were able to identify more than 45 thousand species of spiders, the smallest of which is a spider known as (the Samoan moss spider) with a length of 0.28 mm, and the largest is a bird-eating spider belonging to the tarantula group, where the distance between the ends of two opposite legs of its legs is about 30 cm. spiders also include only a few poisonous species that may pose a danger to human life, including Black Widow, Brown hermit Spider.