Does a snake see with its eyes? Are snakes really deaf? Reptiles

Introduction........................................................ ........................................................ ............3

1. There are many ways to see - it all depends on the goals.................................... ..4

2. Reptiles. General information.............................................................................8

3. Organs of infrared vision of snakes.................................................. ...................12

4. “Heat-visioning” snakes.................................................. ........................................17

5. Snakes strike prey blindly.................................................... .....................20

Conclusion................................................. ........................................................ .......22

References........................................................ ...........................................24

Introduction

Are you sure that the world around us looks exactly the way it appears to us? But animals see it completely differently.

The cornea and lens in humans and higher animals have the same structure. The structure of the retina is similar. It contains light-sensitive cones and rods. Cones are responsible for color vision, rods for vision in the dark.

The eye is an amazing organ of the human body, a living optical device. Thanks to it, we see day and night, distinguish colors and the volume of the image. The eye is designed like a camera. Its cornea and lens, like a lens, refract and focus light. The retina lining the fundus of the eye acts as a sensitive photographic film. It consists of special light-receiving elements - cones and rods.

How do the eyes of our “smaller brothers” work? Animals that hunt at night have more rods in their retinas. Those representatives of the fauna that prefer to sleep at night have only cones in their retinas. The most vigilant in nature are diurnal animals and birds. This is understandable: without acute vision, they simply will not survive. But also the leaders night image The life of animals has its advantages: even with minimal lighting, they notice the slightest, almost imperceptible movements.

In general, humans see more clearly and better than most animals. The fact is that in the human eye there is a so-called yellow spot. It is located in the center of the retina on the optical axis of the eye and contains only cones. They receive rays of light that are least distorted when passing through the cornea and lens.

The “yellow spot” is a specific feature of the human visual apparatus; all other species lack it. It is precisely because of the lack of this important device that dogs and cats see worse than us.

1. There are many ways to see - it all depends on your goals

Each species has evolved its own visual abilities as a result of evolution. as much as is required for its habitat and way of life. If we understand this, we can say that all living organisms have “ideal” vision in their own way.

A person sees poorly under water, but a fish’s eyes are designed in such a way that, without changing its position, it distinguishes objects that for us remain “outside” our vision. U bottom fish, such as flounder and catfish, the eyes are located at the top of the head to see enemies and prey, which usually appear from above. By the way, the eyes of a fish can turn in different directions independently of each other. Predatory fish see under water more clearly than others, as well as inhabitants of the depths that feed on the smallest creatures - plankton and bottom organisms.

Animal vision is adapted to familiar environment. Moles, for example, are short-sighted - they only see up close. But other vision is not needed in the complete darkness of their underground burrows. Flies and other insects have difficulty distinguishing the outlines of objects, but in one second they are able to capture a large number of individual “pictures”. About 200 compared to 18 in humans! Therefore, a fleeting movement, which we perceive as barely perceptible, for a fly is “decomposed” into many individual images - like frames on a film. Thanks to this property, insects instantly find their way when they need to catch their prey in flight or escape from enemies (including people with a newspaper in their hand).

The eyes of insects are one of the most amazing creations nature. They are well developed and occupy most of the surface of the insect's head. They consist of two types - simple and complex. There are usually three simple eyes, and they are located on the forehead in the form of a triangle. They distinguish between light and darkness, and when an insect flies, they follow the horizon line.

Compound eyes consist of many small eyes (facets) that look like convex hexagons. Each eye is equipped with a unique, simple lens. Compound eyes produce a mosaic image - each facet “fits” only a fragment of an object in the field of view.

Interestingly, in many insects, individual facets in compound eyes are enlarged. And their location depends on the insect’s lifestyle. If it is more “interested” in what is happening above it, the largest facets are in the upper part of the compound eye, and if below it, in the lower part. Scientists have repeatedly tried to understand what exactly insects see. Does the world around them really appear before their eyes in the form of a magical mosaic? There is no clear answer to this question yet.

Especially many experiments were carried out with bees. During the experiments, it turned out that these insects need vision for orientation in space, recognition of enemies and communication with other bees. Bees cannot see (or fly) in the dark. But they distinguish some colors very well: yellow, blue, bluish-green, purple and a specific “bee” color. The latter is the result of “mixing” ultraviolet, blue and yellow. In general, bees can easily compete with humans in their visual acuity.

Well, how do creatures who have very poor vision or those who are completely deprived of it get along? How do they navigate in space? Some people also “see” - just not with their eyes. The simplest invertebrates and jellyfish, consisting of 99 percent water, have light-sensitive cells that perfectly replace their usual visual organs.

The vision of the representatives of the fauna inhabiting our planet still holds many amazing secrets, and they are waiting for their researchers. But one thing is clear: all the diversity of eyes in living nature is the result of the long evolution of each species and is closely related to its lifestyle and habitat.

People

We clearly see objects close up and distinguish the finest shades flowers. The cones are located in the center of the retina macular spot"responsible for visual acuity and color perception. View - 115-200 degrees.

On the retina of our eye, the image is recorded upside down. But our brain corrects the picture and transforms it into the “correct” one.

Cats

Wide-set cat eyes provide a 240-degree field of view. The retina of the eye is mainly equipped with rods, the cones are collected in the center of the retina (the area of ​​acute vision). Night vision is better than day vision. In the dark, a cat sees 10 times better than us. Her pupils dilate, and the reflective layer under the retina sharpens her vision. And the cat distinguishes colors poorly - only a few shades.

Dogs

For a long time it was believed that a dog sees the world in black and white. However, canids can still distinguish colors. This information is simply not very meaningful to them.

Canines' vision is 20-40% worse than that of humans. An object that we can distinguish at a distance of 20 meters “disappears” for a dog if it is more than 5 meters away. But night vision is excellent - three to four times better than ours. The dog is a night hunter: it sees far in the dark. In the dark, a guard dog can see a moving object at a distance of 800-900 meters. View - 250-270 degrees.

Birds

Birds hold the record for visual acuity. They distinguish colors well. Most birds of prey visual acuity is several times higher than that of humans. Hawks and eagles spot moving prey from a height of two kilometers. Not a single detail escapes the attention of a hawk soaring at an altitude of 200 meters. His eyes “magnify” the central part of the image by 2.5 times. The human eye does not have such a “magnifier”: the higher we are, the worse we see what is below.

Snakes

The snake has no eyelids. Her eye is covered with a transparent membrane, which is replaced by a new one when molting. The snake focuses its gaze by changing the shape of the lens.

Most snakes distinguish colors, but the outlines of the image are blurred. The snake mainly reacts to a moving object, and only if it is nearby. As soon as the victim moves, the reptile detects it. If you freeze, the snake will not see you. But it can attack. Receptors located near the snake's eyes capture the heat emanating from a living creature.

Fish

The fish's eye has a spherical lens that does not change shape. To focus their gaze, the fish moves the lens closer or further away from the retina using special muscles.

IN clear water the fish sees on average at 10-12 meters, and clearly at a distance of 1.5 meters. But the angle of view is unusually large. Pisces fix objects in a zone of 150 degrees vertically and 170 degrees horizontally. They distinguish colors and perceive infrared radiation.

Bees

“Bees of day vision”: what to look at at night in the hive?

The bee's eye detects ultraviolet radiation. She sees another bee in a purple color and as if through optics that have “compressed” the image.

The bee's eye consists of 3 simple and 2 complex compound ocelli. Complex ones distinguish between moving objects and the outlines of stationary objects during flight. Simple - determine the degree of light intensity. Bees do not have night vision”: what to look at at night in the hive?

2. Reptiles. General information

Reptiles have a bad reputation and few friends among humans. There are many misunderstandings related to their body and lifestyle that have persisted to this day. Indeed, the very word “reptile” means “an animal that creeps” and seems to recall the common idea of ​​them, especially snakes, as disgusting creatures. Despite the prevailing stereotype, not all snakes are poisonous and many reptiles play a significant role in regulating the number of insects and rodents.

Most reptiles are predators with a well-developed sensory system that helps them find prey and avoid danger. They have excellent vision, and snakes, in addition, have a specific ability to focus their gaze by changing the shape of the lens. Nocturnal reptiles, such as geckos, see everything in black and white, but most others have good color vision.

Hearing is not particularly important for most reptiles, and the internal structures of the ear are usually poorly developed. The majority also lack the outer ear, excluding the eardrum, or “tympanum,” which senses vibrations transmitted through the air; From the eardrum they are transmitted through the bones of the inner ear to the brain. Snakes do not have an external ear and can only perceive vibrations that are transmitted along the ground.

Reptiles are characterized as cold-blooded animals, but this is not entirely accurate. Their body temperature is mainly determined environment, but in many cases they can regulate it and, if necessary, maintain it for more high level. Some species are able to generate and retain heat within their own body tissues. Cold blood has some advantages over warm blood. Mammals need to maintain their body temperature at a constant level within very narrow limits. To do this, they constantly need food. Reptiles, on the contrary, tolerate a decrease in body temperature very well; their life span is much wider than that of birds and mammals. Therefore, they are able to inhabit places that are not suitable for mammals, for example, deserts.

Once fed, they can digest food while at rest. In some of the largest species, several months may pass between meals. Large mammals would not survive with this diet.

Apparently, among reptiles, only lizards have well-developed vision, since many of them hunt fast-moving prey. Aquatic reptiles in to a greater extent rely on senses such as smell and hearing to track prey, find a mate, or detect the approach of an enemy. Their vision plays an auxiliary role and operates only at close range, visual images are blurry, and they lack the ability to focus on stationary objects for a long time. Most snakes have fairly poor vision, usually only able to detect moving objects that are nearby. The reaction of numbness in frogs when someone approaches them, for example, is a good thing. defense mechanism, since the snake will not realize the presence of the frog until it makes a sudden movement. If this happens, then visual reflexes will allow the snake to quickly deal with it. Only tree snakes, which coil around branches and grab birds and insects in flight, have good binocular vision.

Snakes have a different sensory system than other hearing reptiles. Apparently, they cannot hear at all, so the sounds of the snake charmer’s pipe are inaccessible to them; they enter a state of trance from the movements of this pipe from side to side. They do not have an external ear or eardrum, but may be able to detect some very low-frequency vibrations using the lungs as sensory organs. Basically, snakes detect prey or an approaching predator by vibrations of the ground or other surface on which they are located. The snake's entire body in contact with the ground acts as one large vibration detector.

Some species of snakes, including rattlesnakes and pit vipers, detect prey by infrared radiation from its body. Under their eyes they have sensitive cells that detect the slightest changes in temperature down to fractions of a degree and, thus, orient the snakes to the location of the prey. Some boas also have sensory organs (on the lips along the mouth opening) that can detect changes in temperature, but these are less sensitive than those of rattlesnakes and pit vipers.

The senses of taste and smell are very important for snakes. The quivering forked tongue of a snake, which some people consider a "snake sting", actually collects traces that quickly disappear into the air various substances and transfers them to sensitive grooves on the inner surface of the mouth. There is a special device in the palate (Jacobson's organ), which is connected to the brain by a branch of the olfactory nerve. Constantly releasing and retracting the tongue is effective method air sampling for important chemical components. When retracted, the tongue is close to the Jacobson's organ, and its nerve endings detect these substances. In other reptiles, the sense of smell plays an important role, and the part of the brain that is responsible for this function is very well developed. The taste organs are usually less developed. Like snakes, the Jacobson's organ is used to detect particles in the air (in some species using the tongue) that carry a sense of smell.

Many reptiles live in very dry places, so keeping water in their bodies is very important to them. Lizards and snakes retain water better than anyone else, but not because of their scaly skin. They lose almost as much moisture through their skin as birds and mammals.

While in mammals high frequency breathing leads to large evaporation from the surface of the lungs; in reptiles, the respiratory rate is much lower and, accordingly, the loss of water through the lung tissue is minimal. Many species of reptiles are equipped with glands that can cleanse salts from the blood and body tissues, releasing them in the form of crystals, thereby reducing the need to separate large volumes of urine. Other unwanted salts in the blood are converted to uric acid, which can be eliminated from the body with minimum quantity water.

Reptile eggs contain everything you need to developing embryo. This is a supply of food in the form of a large yolk, water contained in the protein, and a multi-layered protective shell that does not allow dangerous bacteria to pass through, but allows air to breathe.

The inner membrane (amnion) immediately surrounding the embryo is similar to the same membrane in birds and mammals. The allantois is a thicker membrane that acts as a lung and excretory organ. It ensures the penetration of oxygen and the release of waste substances. The chorion is the membrane surrounding the entire contents of the egg. The outer shell of lizards and snakes is leathery, but in turtles and crocodiles it is harder and calcified, like eggshell in birds.

4. Infrared vision organs of snakes

Infrared vision of snakes requires non-local image processing

The organs that allow snakes to “see” thermal radiation provide an extremely blurry image. Nevertheless, the snake forms a clear thermal picture of the surrounding world in its brain. German researchers have figured out how this can be.

Some species of snakes have a unique ability to capture thermal radiation, allowing them to look at the world around them in absolute darkness. However, they “see” thermal radiation not with their eyes, but with special heat-sensitive organs.

The structure of such an organ is very simple. Next to each eye is a hole about a millimeter in diameter, which leads into a small cavity of approximately the same size. On the walls of the cavity there is a membrane containing a matrix of thermoreceptor cells measuring approximately 40 by 40 cells. Unlike the rods and cones of the retina, these cells do not respond to the “brightness of light” of heat rays, but to the local temperature of the membrane.

This organ works like a camera obscura, a prototype of cameras. A small warm-blooded animal against a cold background emits “heat rays” in all directions - far infrared radiation with a wavelength of approximately 10 microns. Passing through the hole, these rays locally heat the membrane and create a “thermal image”. Thanks to the highest sensitivity of receptor cells (temperature differences of thousandths of a degree Celsius are detected!) and good angular resolution, a snake can notice a mouse in absolute darkness from a fairly long distance.

From a physics point of view, it is precisely good angular resolution that poses a mystery. Nature has optimized this organ so as to better “see” even weak heat sources, that is, it has simply increased the size of the inlet - the aperture. But the larger the aperture, the blurrier the image ( we're talking about, we emphasize, about the most ordinary hole, without any lenses). In a snake situation, where the camera aperture and depth are approximately equal, the image is so blurry that nothing more than “there is a warm-blooded animal somewhere nearby” can be extracted from it. However, experiments with snakes show that they can determine the direction of a point source of heat with an accuracy of about 5 degrees! How do snakes manage to achieve such high spatial resolution with such terrible quality of “infrared optics”?

A recent article by German physicists A. B. Sichert, P. Friedel, J. Leo van Hemmen, Physical Review Letters, 97, 068105 (9 August 2006) was devoted to the study of this particular issue.

Since the real “thermal image,” the authors say, is very blurry, and the “spatial picture” that arises in the animal’s brain is quite clear, it means that there is some kind of intermediate neural apparatus on the way from the receptors to the brain, which, as it were, adjusts the sharpness of the image. This apparatus should not be too complex, otherwise the snake would “think about” each image received for a very long time and would react to stimuli with a delay. Moreover, according to the authors, this device is unlikely to use multi-stage iterative mappings, but is, rather, some kind of fast one-step converter that works according to a permanently hardwired nervous system program.

In their work, the researchers proved that such a procedure is possible and quite realistic. They spent mathematical modeling how a “thermal image” appears, and developed an optimal algorithm for repeatedly improving its clarity, dubbing it a “virtual lens”.

Despite the big name, the approach they used, of course, is not something fundamentally new, but just a type of deconvolution - restoring an image spoiled by the imperfection of the detector. This is the reverse of image blurring and is widely used in computer image processing.

In the analysis, however, there was important nuance: The deconvolution law did not need to be guessed; it could be calculated based on the geometry of the sensitive cavity. In other words, it was known in advance what specific image would be produced by a point source of light in any direction. Thanks to this, a completely blurred image could be restored with very good accuracy (ordinary graphic editors with a standard deconvolution law would not have been able to cope even close to this task). The authors also proposed a specific neurophysiological implementation of this transformation.

Whether this work said any new word in the theory of image processing is a moot point. However, it undoubtedly led to unexpected conclusions regarding the neurophysiology of “infrared vision” in snakes. Indeed, the local mechanism of “ordinary” vision (each visual neuron takes information from its own small area on the retina) seems so natural that it is difficult to imagine something very different. But if snakes really use the described deconvolution procedure, then each neuron that contributes to the whole picture of the surrounding world in the brain receives data not from a point at all, but from a whole ring of receptors running throughout the membrane. One can only wonder how nature managed to construct such “non-local vision”, compensating for defects in infrared optics with non-trivial mathematical transformations of the signal.

Infrared detectors, of course, are difficult to distinguish from the thermoreceptors discussed above. The Triatoma thermal bedbug detector could be discussed in this section. However, some thermoreceptors are so specialized in detecting distant heat sources and determining the direction towards them that they are worth considering separately. The most famous of these are the facial and labial pits of some snakes. The first indications are that the family of pseudopods Boidae (boa constrictors, pythons, etc.) and the subfamily of pit vipers Crotalinae (rattlesnakes, including the true rattlesnake Crotalus and the bushmaster (or surukuku) Lachesis) have infrared sensors, were obtained from an analysis of their behavior when searching for victims and determining the direction of attack. Infrared detection is also used for defense or escape, which is caused by the appearance of a heat-emitting predator. Subsequently, electrophysiological studies of the trigeminal nerve innervating the labial fossae of propopods and the facial fossae of pit snakes (between the eyes and nostrils) confirmed that these recesses indeed contain infrared receptors. Infrared radiation provides an adequate stimulus to these receptors, although a response can also be generated by washing the fossa with warm water.

Histological studies have shown that the pits do not contain specialized receptor cells, but unmyelinated endings of the trigeminal nerve, forming a wide, non-overlapping branching.

In the pits of both pseudopods and pit snakes, the surface of the bottom of the pit reacts to infrared radiation, and the reaction depends on the location of the radiation source relative to the edge of the pit.

Activation of receptors in both pseudopods and pit snakes requires a change in the flow of infrared radiation. This can be achieved either as a result of the movement of a heat-emitting object in the "field of view" relative to the colder surroundings, or by the scanning movement of the snake's head.

The sensitivity is sufficient to detect the radiation flux from a human hand moving in the “field of view” at a distance of 40 - 50 cm, which means that the threshold stimulus is less than 8 x 10-5 W/cm2. Based on this, the temperature increase detected by the receptors is on the order of 0.005 ° C (i.e., approximately an order of magnitude better than the human ability to detect temperature changes).

5. Heat-visioning snakes

Experiments carried out by scientists in the 30s of the 20th century with rattlesnakes and related pit snakes (crotalids) showed that snakes can actually see the heat emitted by a flame. Reptiles were able to detect at great distances the subtle heat emitted by heated objects, or, in other words, they were able to sense infrared radiation, the long waves of which are invisible to humans. The ability of pit snakes to sense heat is so great that they can sense the heat emitted by a rat from a considerable distance. Snakes have heat sensors in small pits on their snouts, hence their name - pitheads. Each small, forward-facing pit located between the eyes and nostrils has a tiny, pinprick-like hole. At the bottom of these holes there is a membrane, similar in structure to the retina of the eye, containing the smallest thermoreceptors in quantities of 500-1500 per square millimeter. Thermoreceptors have 7,000 nerve endings connected to a branch of the trigeminal nerve located on the head and muzzle. Because the sensory zones of both pits overlap, the pit snake can perceive heat stereoscopically. Stereoscopic perception of heat allows the snake, by detecting infrared waves, not only to find prey, but also to estimate the distance to it. Fantastic thermal sensitivity is combined in pit snakes with a quick response, allowing snakes to respond instantly, in less than 35 milliseconds, to a thermal signal. It is not surprising that snakes with this reaction are very dangerous.

The ability to detect infrared radiation gives pit vipers significant capabilities. They can hunt at night and stalk their main prey, rodents, in their underground burrows. Although these snakes have a highly developed sense of smell, which they also use to find prey, their deadly strike is guided by heat-sensitive pits and additional thermoreceptors located inside the mouth.

Although infrared sense in other groups of snakes is less well understood, boa constrictors and pythons are also known to have heat-sensitive organs. Instead of pits, these snakes have more than 13 pairs of thermoreceptors located around the lips.

There is darkness in the depths of the ocean. The light of the sun does not reach there, and only the light emitted there flickers deep sea inhabitants seas. Like fireflies on land, these creatures are equipped with organs that generate light.

Possessing a huge mouth, the black malacoste (Malacosteus niger) lives in complete darkness at depths from 915 to 1830 m and is a predator. How can he hunt in complete darkness?

Malacost is able to see what is called far red light. Light waves in the red part of the so-called visible spectrum have the longest wavelength, around 0.73-0.8 micrometers. Although this light is invisible to the human eye, some fish, including the black malacoste, can see it.

On the sides of a malacoste's eyes are a pair of bioluminescent organs that emit a blue-green light. Most other bioluminescent creatures in this realm of darkness also emit a bluish light and have eyes that are sensitive to the blue wavelengths of the visible spectrum.

The black malacoste's second pair of bioluminescent organs are located below its eyes and produce a distant red light that is invisible to others living in the depths of the ocean. These organs give the black malacoste an advantage over its rivals, as the light it emits helps it see prey and allows it to communicate with other members of its species without revealing its presence.

But how does the black malacost see far red light? According to the saying, "You are what you eat," it actually gets this opportunity by eating tiny copepods, which in turn feed on bacteria that absorb far-red light. In 1998, a team of scientists in the UK, including Dr. Julian Partridge and Dr. Ron Douglas, discovered that the retina of the black malacoste's eyes contains a modified version of the bacterial chlorophyll, a photopigment that can detect rays of far-red light.

Thanks to far-red light, some fish can see in water that would appear black to us. Bloodthirsty Piranha in the murky waters of the Amazon, for example, it perceives the water as dark red, a color more permeable than black. The water appears red due to red-colored vegetation particles that absorb visible light. Only far red light rays pass through muddy water, and the piranha can see them. Infrared rays allow it to see prey, even if it hunts in complete darkness. Just like piranha, crucian carp in their natural habitats fresh water often muddy and overcrowded with vegetation. And they adapt to this by being able to see far red light. Indeed, their visual range (level) exceeds that of the piranha, since they can see not only in far-red light, but also in true infrared light. So your favorite is homemade goldfish can see much more than you think, including the "invisible" infrared rays emitted by common household electronic devices such as television remote control and security alarm system beams.

5. Snakes strike prey blindly

It is known that many species of snakes, even when deprived of vision, are capable of striking their victims with supernatural accuracy.

The rudimentary nature of their thermal sensors makes it difficult to argue that the ability to perceive the heat radiation of prey alone can explain these amazing abilities. A study by scientists from the Technical University of Munich shows that it's probably all about snakes having a unique "technology" for processing visual information, Newscientist reports.

Many snakes have sensitive infrared detectors, which helps them navigate in space. In laboratory conditions, snakes' eyes were covered with adhesive tape, and it turned out that they were capable of infecting a rat. instant blow poisonous teeth into the victim's neck or behind the ears. Such accuracy cannot be explained solely by the snake's ability to see the heat spot. Obviously, the whole point is in the ability of snakes to somehow process the infrared image and “clean” it from interference.

Scientists have developed a model that takes into account and filters both thermal “noise” emanating from moving prey, as well as any errors associated with the functioning of the detector membrane itself. In the model, a signal from each of 2 thousand thermal receptors causes excitation of its neuron, but the intensity of this excitation depends on the input to each of the others nerve cells. By integrating signals from interacting receptors into the models, scientists were able to obtain very clear thermal images even with high levels of extraneous noise. But even relatively small errors associated with the operation of membrane detectors can completely destroy the image. To minimize such errors, the thickness of the membrane should not exceed 15 micrometers. And it turned out that the membranes of pit snakes have exactly this thickness, says cnews.ru.

Thus, scientists were able to prove the amazing ability of snakes to process even images that are very far from perfect. Now it's a matter of confirming the model with studies of real snakes.

Conclusion

It is known that many species of snakes (in particular from the group of pit snakes), even being deprived of vision, are capable of striking their victims with supernatural “accuracy”. The rudimentary nature of their thermal sensors makes it difficult to argue that the ability to perceive the heat radiation of prey alone can explain these amazing abilities. A study by scientists from the Technical University of Munich shows that it may be because snakes have a unique “technology” for processing visual information, Newscientist reports.

It is known that many snakes have sensitive infrared detectors, which help them navigate in space and detect prey. In laboratory conditions, snakes were temporarily deprived of vision by covering their eyes with a plaster, and it turned out that they were able to hit a rat with an instant blow of poisonous teeth aimed at the victim’s neck, behind the ears - where the rat was not able to fight back with its sharp incisors. Such accuracy cannot be explained solely by the snake's ability to see a vague heat spot.

On the sides of the front of the head, pit snakes have depressions (which give the group its name) in which heat-sensitive membranes are located. How does a thermal membrane “focus”? It was assumed that this organ works on the principle of a camera obscura. However, the diameter of the holes is too large to implement this principle, and as a result, only a very blurry image can be obtained, which is not capable of providing unique accuracy snake throw. Obviously, the whole point is in the ability of snakes to somehow process the infrared image and “clean” it from interference.

Scientists have developed a model that takes into account and filters both thermal “noise” emanating from moving prey, as well as any errors associated with the functioning of the detector membrane itself. In the model, a signal from each of the 2 thousand thermal receptors causes the excitation of its neuron, but the intensity of this excitation depends on the input to each of the other nerve cells. By integrating signals from interacting receptors into the models, scientists were able to obtain very clear thermal images even with high levels of extraneous noise. But even relatively small errors associated with the operation of membrane detectors can completely destroy the image. To minimize such errors, the thickness of the membrane should not exceed 15 micrometers. And it turned out that the membranes of pit snakes have exactly this thickness.

Thus, scientists were able to prove the amazing ability of snakes to process even images that are very far from perfect. All that remains is to confirm the model with studies of real, not “virtual” snakes.

References

1. Anfimova M.I. Snakes in nature. - M, 2005. - 355 p.

2. Vasiliev K.Yu. Reptile vision. - M, 2007. - 190 p.

3. Yatskov P.P. Snake breed. - St. Petersburg, 2006. - 166 p.

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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 studied quite well, 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 have collected 10 of the most common myths about snakes and refuted 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 may end in failure. 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 in South America– 72 species. The rest are almost equally distributed across Australia, Central Africa, Southeast 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 only snakes of other species as food. So, what exactly to feed the snake depends only on the snake itself.

Snakes are cold to the touch

Snakes are typical representatives of cold-blooded animals. And therefore the body temperature of the snake will be the same as the temperature of the external environment. Therefore, not being able to maintain optimal body temperature (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.
My royal python or ball python or python regius (Python regius)

Remember the movie "The Speckled Band"? There they whistled to call the snake, and then there was a conversation that snakes were deaf and so on. So, I hasten to inform you that snakes are not deaf at all! But they hear a little differently, or rather not at all like we do.
Let us recall the biology course: the organ of hearing consists of the outer ear, the eardrum, to which bones from one to three are connected (depending on the type of animal) they transmit a signal to the cochlea, a three-dimensional spiral-twisted organ in which there are ciliated cells that actually read sound vibrations due to the fluid filling the cochlea. Well, something like this. What's the problem with snakes? And they do not have an eardrum, nor an external organ of hearing.

But there is a cochlea (blue) and an auditory ossicle (green). And not only that, the auditory ossicle (green) is attached to the large quadrate bone (blue). So why? Ahh... this is where the fun begins! The square bone, together with the jaw, replaces the eardrum. It turns out to be a kind of resonator due to a system of levers, which perceives vibration from the ground and low-frequency waves. The snake can hear you several meters away, even if you walk carefully and quietly. But whistling at a snake like in the movies is really useless. But they perfectly distinguish all the low sounds that we hear. Let’s say from my snakes, I see how they flinch from the low bark of my dogs, and how they smell a heavy car driving on the street, and we ourselves are on the fifth floor.

What else is interesting about snakes? And they have thermoreception. These are thermopits in vipers, pythons, boas, and some strange African colubrids.

Here you can clearly see the thermopits on my Python regius on the upper jaw

The most advanced thermal apparatus, let's say, is that of pit vipers ( Crotalinae). There, inside each hole there are several layers of membranes and a bunch of different thermoreceptors. They are all terribly sensitive! No, they don't see like a thermal imager! Don’t believe the BBC films - the snake doesn’t see any outline of anything there. There is no rhodopsin protein in thermopits; information is read there due to ion channels in the receptor membranes! they show the strength of the object's heat radiation and the direction towards it. All.

In general, whatever you say: but in terms of the number of sense organs and their complexity, the snake will surpass almost any land animal. Next time I’ll tell you how snakes see and why they stick out their tongues.
Well, about the evolution of their poisonous apparatus - that’s a whole different story!

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 Volga region and the Central Asian steppes to Transbaikalia and Ussuri taiga, there are medium-sized poisonous snakes, nicknamed copperheads: their heads are covered on top not with small scales, but with large shields.

People who have examined 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 of America's rattlesnakes, which locals sometimes call quartonaris, that is, four-nosed snakes. 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 organs. 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 outwards 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 was communicating with external environment a narrow and long canal that 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 great job, 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. They brought the snakes wrapped in black paper light bulbs. 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 you brought a heated object closer to the snake’s head, even just human hand(at a distance of 30 centimeters), as 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, in the thermoscopic eyes of squids, the perception of a heat-emitting 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 subjected to different sides exposed 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.