How many eyes does a spider have: photo and structure of the visual organs

The number of eyes on spiders varies from zero to eight. While most species of spiders have 8 eyes, some spiders, such as Sinopoda Scurion, have no eyes at all!

Arachnophobia, the fear of arachnids, especially spiders, is one of the most common animal phobias. In fact, a study claims that almost 3.5% to 6% of the world's population is afraid of spiders. However, what makes these multi-legged crawling creatures so scary? Is it the fact that they appear and disappear almost instantly? They can be there one second and disappear in the blink of an eye. Poof! Or do movies depict spiders? Or maybe it's the number of beady eyes looking at you? Speaking of eyes...how many eyes should you worry about?

Number of eyes in spiders

A striking difference between spiders and insects is the number of legs, there are always 8 of them. The same cannot be said about the organs of vision. There is no exact number of spider eyes, the figure ranges from 2 to 8 pieces. The largest number of species have exactly eight of them, however:

Caponiidae is a family of small spiders, most of whose representatives have 2 eyes. But during the development of individuals, the number of eyes may change;
Cute big-eyed jumping spider.
Symphytognathates, Uloboridae have 4 eyes;
Tubulars, Spitters have 6 eyes;
There are species, mainly inhabitants of dark caves, that are completely devoid of visual organs.

Simple and complex vision of arthropods

Insects have the most developed vision. In this regard, the eyes of arachnids are often called simple. In developed representatives of insects - bees, dragonflies, flies and the like - compound eyes have a facet structure. The structural visual unit is the ommatidia. These, in fact, make up a complex optical system. Located side by side, they form a visual complex. The ommatidium consists of a biconvex lens (cornea), under which there is a transparent cone, similar in properties to the lens.

Features of the organs of vision

At least 2 or 8 eyes have operating features. To ensure they work in unison and give a complete overview, they are separated and have different functions.

Primary eyes

Spider eye: 1. Muscles 2. Retina 3. Lens

The primary ones are most often the main pair, which is located straight. They have clearly defined edges, but they are motionless. The primary eyes have several functions:

collection of parts;
focusing on an object;
image tracking.

The latter is possible due to the fact that the spider's eyes have muscles that move the retina.

Secondary eyes

Spider eyes.

They are located next to the primary ones and can be located on the sides, in the middle or in the second row. Their main functions depend on the type of spider, but the general meanings are:

motion capture;
hazard analyzer;
enhance vision in low humidity conditions.

Compound eyes

Not all types of spiders have them, only some have them left over from their ancestors. The main function is to notice and reflect light. Due to them, there are no blind spots for the animal.

Types of spiders.

Visual system

In the process of evolution, different types of arachnids have developed a special vision structure. Hunting techniques and lifestyle depend on how many eyes the animal has.

Spiders that hunt by weaving webs have poor eyesight. More active hunters see much better. Basically, visual elements are represented by four pairs , arranged in 2 rows. The need for a large number of eyes is explained by the animal’s lifestyle. Arachnids have access to a 360-degree view.

However, in nature there are varieties that have 12 eyes, but there are also those who make do with one pair of visual elements.

However, these individuals also fully exist, because in nature every little detail is thought out.

How do spider eyes work?

The spider's eyes provide them with excellent visibility and good quality of vision. Some individuals are even sensitive to ultraviolet light. Interestingly, the mechanism works the other way around:

first, the lateral organs of vision are turned on, which see the victim or danger for a long time;
then the primary eyes are turned on, which focus on the object and analyze, regulating further actions.

In fact, the spider first catches movement with its side eyes, and then turns to look close-up with its main ones.

Nutrition

The main diet consists of insects of different sizes. The spider's trapping nets catch flies, wasps, hornets, grasshoppers, locusts, caterpillars, and butterflies. Snakes, frogs, toads, and mice get entangled in large, strong webs.

Cross spider

There is no internal digestive system, food liquefaction occurs externally. The spider bites the victim, injects poison that paralyzes the muscles and immobilizes the prey. The cross releases saliva into the insect’s body, envelops it in a web, and waits for several minutes. In 5-20 minutes, the insides of the prey turn into a liquid mass, which the predator sucks up.

Virtues of vision

Spider with 8 eyes.

Spiders, thanks to their vision, have many advantages over other animals. The advantages are:

the detail is better, people have weeks;
ability to look at a picture close-up;
good quality of vision in ultraviolet;
ability to monitor prey around;
Accurate jumping and movement in the grass, thanks to the ability to determine distance.

Scorpios: lifestyle

These arthropods are most often found in regions with tropical climates. Some species are diurnal, but the vast majority are nocturnal hunters. They prefer to hide from the scorching heat and hide under stones, snags and other secluded places during this period.

This is partly due to their imperfect vision. They can only notice danger at close range, and are better suited to hunting at night. But this is not only due to the specific features of vision. It doesn’t matter how many eyes a scorpion has (photo below) - they do not play a decisive role in capturing prey. It is believed that the main merit of precise attacks is the sensitive sensors on their paws.

Circular positioning of the legs gives the scorpion the opportunity to feel the smallest vibrations of the soil from all sides. Based on the speed of propagation of such signals (the nearest paws sense them earlier), it determines the exact location of the prey. The eyes play a secondary role in this. It has been noticed that if a scorpion and a victim are separated by a barrier in the form of a thin crevice, it will not be able to attack it even at close range. In this case, soil signals from the movement of prey do not reach its sensitive paws.

Basics

The tarantula's body is divided into two parts - the cephalothorax and abdomen. The cephalothorax contains the main central control organ of the spider - the brain. It is not for nothing that wolf spiders are called one of the smartest arachnids, because their brain volume occupies approximately 30% of the total cephalothorax space!

Four pairs of legs covered with fine hairs are also attached to it. The abdomen of the tarantula is also covered with them. This is his secret weapon.

In case of threat, the tarantula spider rises on its hind legs, and with its front legs it quickly, quickly scrapes off these fibers, which, when they fall on an enemy, say, on a person, cause him an unpleasant itch, like glass wool. But this is not as dangerous as it might seem, the irritation goes away quite quickly.

Danger to humans

This type of arthropod belongs to the category of weakly poisonous arachnids and is not at all prone to attacking warm-blooded animals or people. When danger is detected, the wolf spider quickly turns over with its belly up and stops showing signs of life. In this relatively uncomfortable position for arthropods, without movement, the spider can remain for a long time, until the threat has completely passed.

There are known cases where a sharp and sudden attack on a wolf spider caused aggression in it and provoked the arthropod to bite, which is not capable of directly threatening human life, but can cause pain, redness of the skin and moderate swelling. In this case, it is recommended to apply an ice pack to the bite site, as well as take any antihistamine.

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If I don’t eat it, I’ll bite you!

The structure of the tarantula has one more feature - huge chelicerae. These are the "jaws" of the spider. With them he captures prey and injects poison.

The tarantula's digestive system consists of two stomachs, as well as an intestine and a digestive gland - the liver.

The circulatory system of a tarantula is a tube with a branched network of vessels extending from it, through which a clear liquid flows - the so-called hemolymph.

The tarantula breathes with the help of special holes in the exoskeleton - spiracles. Through them, air enters the spider's lungs, which also have an unusual structure. They are also called pulmonary books, since one of the walls of each of the two lungs is folded like book pages.

Although the tarantula does not spin webs, it does have arachnoid glands. He lines the burrow with this web, and the female weaves a cocoon for her eggs.

Nutrition

Cross spider

General characteristics. External structure

The cross spider can be found in the forest, park, and on the window frames of village houses and cottages. Most of the time, the spider sits in the center of its trapping network of adhesive thread - cobweb.

The spider's body consists of two sections: a small elongated cephalothorax and a larger spherical abdomen. The abdomen is separated from the cephalothorax by a narrow constriction. Four pairs of walking legs are located on the sides of the cephalothorax. The body is covered with a light, durable and quite elastic chitinous cover.

The spider periodically moults, shedding its chitinous cover. At this time it is growing. At the anterior end of the cephalothorax there are four pairs of eyes, and below there is a pair of hook-shaped hard jaws - chelicerae. With them the spider grabs its prey.

There is a canal inside the chelicerae. Through the channel, poison from the poisonous glands located at their base enters the victim’s body. Next to the chelicerae there are short organs of touch, covered with sensitive hairs - the tentacles.

At the lower end of the abdomen there are three pairs of arachnoid warts that produce cobwebs - these are modified abdominal legs.

The liquid released from arachnoid warts instantly hardens in air and turns into a strong web thread. Different parts of arachnoid warts produce different types of webs. Spider threads vary in thickness, strength, and adhesiveness. The spider uses different types of web to build a trapping network: at its base there are stronger and non-sticky threads, and concentric threads are thinner and stickier. The spider uses webs to strengthen the walls of its shelters and to make cocoons for eggs.