How a snake sees a person. Reptile visual organs. Snakes always attack when they see people

There are about three thousand snakes on earth. They belong to the scaly order and like to live in places warm climate. Many, walking through the forest in an area where snakes can live, wonder if they can see us? Or should we look at our feet so as not to disturb the reptile? The fact is that among the diversity in the animal world, only the eyes of a snake are capable of determining shades and colors, but their visual acuity is weak. For a snake, vision is, of course, important, but not as important as smell. IN old times people paid attention to the snake's eye, considering it cold and hypnotic.

How does a snake's eye work?

Reptiles have very dull eyes. This is because they are covered with a film that changes during molting along with the rest of the skin. Because of this, snakes have poor visual acuity. As soon as reptiles shed their skin, their visual acuity immediately increases. During this period they see best. They feel this way for several months.

Most people believe that all snakes are poisonous without exception. This is wrong. Large quantity species are completely harmless. Poisonous reptiles They use poison only in case of danger and when hunting. It occurs both during the day and at night. Depending on this, the pupil changes its shape. So, during the day it is round, and at night it is stretched into a gap. There are whip snakes with an inverted keyhole pupil. Each eye is capable of forming an entire picture of the world.

For snakes, the main organ is the sense of smell. They use it as thermolocation. So, in complete silence, they feel the heat generated by a possible victim and indicate its location. Not poisonous species they pounce on their prey and strangle it, some of them begin to swallow it alive. It all depends on the size of the reptile itself and its prey. On average, the body of a snake is about one meter. There are both small and large species. Directing their gaze at the victim, they focus it. At this time, their tongue picks up the slightest odors in space.

Thermal locators of a different design have recently been studied in snakes. This discovery is worth telling in more detail.

In the east of the USSR, from the Caspian Trans-Volga region and the Central Asian steppes to Transbaikalia and the Ussuri taiga, there are small poisonous snakes, nicknamed copperheads: their heads are covered on top not with small scales, but with large shields.

People who have looked at copperheads up close claim that these snakes seem to have four nostrils. In any case, on the sides of the head (between the real nostril and the eye) two large (larger than the nostril) and deep pits are clearly visible in copperheads.

Cottonmouths are close relatives rattlesnakes America, which local residents sometimes called quartonarians, that is, four-nosed. This means that rattlesnakes also have strange pits on their faces.

Zoologists combine all snakes with four “nostrils” into one family, the so-called crotalids, or pitheads. Pit snakes are found in America (North and South) and Asia. In their structure they are similar to vipers, but differ from them in the mentioned pits on the head.

For more than two hundred years, scientists have been solving nature's puzzle, trying to establish what role these pits play in the life of snakes. What assumptions were made!

They thought that these were organs of smell, touch, hearing amplifiers, glands that secrete lubricant for the cornea of ​​the eyes, detectors of subtle air vibrations (like the lateral line of fish) and, finally, even air blowers that deliver oxygen to the oral cavity, supposedly necessary for the formation of poison.

Thorough research by anatomists thirty years ago showed that the facial pits of rattlesnakes are not connected to the ears, eyes, or

any other known authorities. They are depressions in the upper jaw. Each pit at a certain depth from the inlet is divided by a transverse partition (membrane) into two chambers - internal and external.

The external chamber lies in front and opens outward with a wide funnel-shaped opening, between the eye and nostril (in the area of ​​the auditory scales). The rear (inner) camera is completely closed. Only later was it possible to notice that it communicates with the external environment through a narrow and long channel, which opens on the surface of the head near the anterior corner of the eye with an almost microscopic pore. However, the size of the pore, when necessary, can apparently increase significantly: the opening is equipped with an annular closing muscle.

The partition (membrane) separating both chambers is very thin (about 0.025 millimeters thick). Dense interweaving of nerve endings penetrates it in all directions.

Undoubtedly, the facial pits represent organs of some senses. But which ones?

In 1937, two American scientists, D. Noble and A. Schmidt, published a large work in which they reported the results of their many years of experiments. They managed to prove, the authors argued, that the facial pits are thermolocators! They capture heat rays and determine by their direction the location of the heated body emitting these rays.

D. Noble and A. Schmidt experimented with rattlesnakes artificially deprived of all known to science sense organs. Electric light bulbs wrapped in black paper were brought to the snakes. While the lamps were cold, the snakes did not pay any attention to them. But when the light bulb got hot, the snake immediately felt it. She raised her head and became wary. The light bulb was brought even closer. The snake made a lightning-fast throw and bit the warm “victim.” I didn’t see her, but she bit her accurately, without missing a beat.

Experimenters have found that snakes detect heated objects whose temperature is at least 0.2 degrees Celsius higher than the surrounding air (if they are brought closer to the muzzle itself). Warmer objects are recognized at a distance of up to 35 centimeters.

In a cold room, thermolocators work more accurately. They are apparently adapted for night hunting. With their help, the snake searches for small warm-blooded animals and birds. It is not the smell, but the warmth of the body that gives away the victim! Snakes have poor eyesight and sense of smell and very poor hearing. A new, very special feeling came to their aid - thermal location.

In the experiments of D. Noble and A. Schmidt, the indicator that the snake had found a warm light bulb was its throw. But the snake, of course, even before it rushed to attack, already felt the approach of a warm object. This means that we need to find some other, more accurate signs by which one could judge the subtlety of the snake’s thermolocation sense.

American physiologists T. Bullock and R. Cowles conducted more thorough studies in 1952. As a signal notifying that an object was detected by the snake's thermolocator, they chose not the reaction of the snake's head, but a change in biocurrents in the nerve serving the facial fossa.

It is known that all processes of excitation in the body of animals (and humans) are accompanied by those occurring in the muscles and nerves. electric currents. Their voltage is low - usually hundredths of a volt. These are the so-called “biocurrents of excitation”. Biocurrents are easy to detect using electrical measuring instruments.

T. Bullock and R. Cowles anesthetized snakes by injecting a certain dose of curare poison. We cleared one of the nerves branching in the membrane of the facial fossa from muscles and other tissues, brought it out and pressed it between the contacts of a device that measures biocurrents. Then the facial pits were subjected to various influences: they were illuminated with light (without infrared rays), strong-smelling substances were brought close to them, and they were irritated with strong sound, vibration, and pinches. The nerve did not react: biocurrents did not arise.

But as soon as a heated object, even just a human hand (at a distance of 30 centimeters), was brought closer to the snake’s head, excitement arose in the nerve - the device recorded biocurrents.

They illuminated the pits with infrared rays - the nerve became even more excited. The weakest reaction of the nerve was detected when it was irradiated with infrared rays with a wavelength of about 0.001 millimeters. As the wavelength increased, the nerve became more excited. The greatest reaction was caused by the longest wavelength infrared rays (0.01 - 0.015 millimeters), that is, those rays that carry the maximum thermal energy emitted by the body of warm-blooded animals.

It also turned out that the thermolocators of rattlesnakes detect not only objects that are warmer, but even colder than the surrounding air. It is only important that the temperature of this object is at least a few tenths of a degree higher or lower than the surrounding air.

The funnel-shaped openings of the facial fossae are directed obliquely forward. Therefore, the thermolocator's coverage area lies in front of the snake's head. Up from the horizontal it occupies a sector of 45 degrees, and downward - 35 degrees. To the right and left of the longitudinal axis of the snake’s body, the field of action of the thermolocator is limited to an angle of 10 degrees.

Physical principle, on which the thermolocators of snakes are based, is completely different from that of squids.

Most likely, perception is in the thermoscopic eyes of squids radiating heat object is achieved through photochemical reactions. Processes of the same type probably occur here as on the retina of an ordinary eye or on a photographic plate at the time of exposure. The energy absorbed by the organ leads to the recombination of light-sensitive (in squids, heat-sensitive) molecules, which act on the nerve, causing the brain to imagine the observed object.

Snake thermal locators They act differently - on the principle of a kind of thermoelement. The thinnest membrane separating the two chambers of the facial fossa is exposed from different sides to two different temperatures. The internal chamber communicates with the external environment through a narrow channel, the inlet of which opens in the opposite direction from the working field of the locator.

Therefore, the ambient air temperature is maintained in the inner chamber (neutral level indicator!) The outer chamber is directed towards the object under study with a wide opening - a heat trap. The heat rays it emits heat the front wall of the membrane. Based on the temperature difference on the inner and outer surfaces of the membrane, which are simultaneously perceived by the nerves in the brain, the sensation of radiating thermal energy subject.

In addition to pit snakes, thermolocation organs have been found in pythons and boas (in the form of small pits on the lips). The small pits located above the nostrils of the African, Persian and some other species of vipers apparently serve the same purpose.

Snakes are one of the most mysterious inhabitants of our planet. Primitive hunters, when meeting any snake, hurried to escape from it, knowing that just one bite could doom them to death. Fear helped avoid being bitten, but prevented us from learning more about these mysterious creatures. And where precise knowledge was lacking, the gaps were filled by fantasies and conjectures, which became more and more sophisticated over the centuries. And, despite the fact that many of these reptiles have already been quite well studied, old rumors and legends about snakes, passed down from generation to generation, still dominate the minds of people. To somehow break this vicious circle, we've collected 10 of the most common myths about snakes and debunked them.

Snakes drink milk

This myth became known to many of us thanks to Conan Doyle’s “The Speckled Band.” In fact, trying to feed a snake milk can be fatal: they do not digest lactose at all.

When attacking, snakes sting

For unknown reasons, many people believe that snakes sting with their sharp, forked tongue. Snakes bite with their teeth, like all other animals. Language serves them for completely different purposes.

Before throwing, snakes stick out their tongues threateningly.

As already stated, a snake's tongue is not intended to attack. The fact is that snakes do not have a nose, and all the necessary receptors are located on their tongue. Therefore, in order to better smell the scent of prey and determine its location, snakes have to stick out their tongues.

Most snakes are poisonous

Of the two and a half thousand species of snakes known to serpentologists, only 400 have poisonous teeth. Of these, only 9 are found in Europe. Most poisonous snakes V South America– 72 species. The rest are almost equally distributed across Australia, Central Africa, South-East Asia, Central and North America.

You can “safety” a snake by pulling out its teeth

This might actually work for a while. But the teeth will grow back, and the snake during the period of their growth, not being able to express the venom, can become seriously ill. And by the way, it is impossible to train a snake - for them, any person is nothing more than just a warm tree.

Snakes always attack when they see people

Statistics show that most often snakes bite people in self-defense. If a snake hisses and makes threatening movements when it sees you, it means it just wants to be left alone. As soon as you retreat a little, the snake will immediately disappear from view, rushing to save its life.

Snakes can be fed meat

Most snakes eat rodents, but there are species that eat frogs and fish and even insectivorous reptiles. A king cobras, for example, they prefer to eat only snakes of other species. So, what exactly to feed the snake depends only on the snake itself.

Snakes are cold to the touch

Snakes are typical representatives cold-blooded animals. And therefore the snake's body temperature will be the same as the temperature external environment. Therefore, without being able to support optimal temperature bodies (just above 30 ° C), snakes love to bask in the sun.

Snakes covered in mucus

Another story that has nothing to do with snakes. The skin of these reptiles contains virtually no glands and is covered with dense, smooth scales. It is from this pleasant-to-touch snake skin that shoes, handbags and even clothes are made.

Snakes wrap around branches and tree trunks

Quite often you can see the image of the tempting serpent entwining the trunk of the tree of knowledge. However, this has nothing to do with their actual behavior. Snakes climb onto tree branches and lie on them, but they have absolutely no need to wrap their bodies around them.

Sense organs in snakes

In order to successfully detect, overtake and kill animals, snakes have at their disposal a rich arsenal of various devices that allow them to hunt depending on the prevailing circumstances.

One of the first places in importance among snakes is the sense of smell. Snakes have a surprisingly delicate sense of smell, capable of detecting the smell of the most insignificant traces of certain substances. The snake's sense of smell involves a forked, mobile tongue. The flickering tongue of a snake is as common a touch to a portrait as the absence of limbs. Through the trembling touches of the tongue, the snake “touches” - touches. If the animal is nervous or is in an unusual environment, the frequency of tongue flickering increases. With quick movements “outward - into the mouth,” she seems to take a sample of the air, receiving detailed chemical information about the environment. The forked tip of the tongue, curving, presses against two small pits on the palate - Jacobson's organ, consisting of chemically sensitive cells, or chemoreceptors. By vibrating its tongue, the snake captures microscopic particles of odorous substances and brings them to this unique organ of taste and smell for analysis.

Snakes lack auditory openings and eardrums, making them deaf in the usual sense. Snakes do not perceive sounds that are transmitted through the air, but they subtly detect vibrations passing through the soil. They perceive these vibrations with their ventral surface. So the snake is absolutely indifferent to screams, but it can be scared by stomping.

Snakes' vision is also quite weak and is of little importance to them. There is an opinion that snakes have some kind of special hypnotic snake look and can hypnotize their prey. In fact, there is nothing like that, it’s just that, unlike many other animals, snakes do not have eyelids, and their eyes are covered with transparent skin, so the snake does not blink, and its gaze seems intent. And the shields located above the eyes give the snake a gloomy, angry expression.

Three groups of snakes - boas, pythons and pit vipers - have a unique additional sensory organ that no other animal has.
This is a thermolocation organ, presented in the form of thermolocation pits on the snake’s face. Each hole is deep and covered with a sensitive membrane, which senses temperature fluctuations. With its help, snakes can detect the location of a warm-blooded animal, i.e. their main prey, even in complete darkness. Moreover, by comparing signals received from fossae on opposite sides of the head, i.e. Using the stereoscopic effect, they can accurately determine the distance to their prey and then strike. Boas and pythons have a whole series of such pits located in the labial scutes bordering the upper and lower jaw. Pit vipers have only one pit on each side of their head.

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