Program “I love Psychology” 

Do snakes have vision? How do snakes compensate for their poor development of vision and hearing? Comment from drlinux

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

Bibliography................................................ ...........................................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 nocturnal animals also have their 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. Bottom-dwelling fish such as flounder and catfish have eyes located at the top of their heads to see enemies and prey that 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.

The vision of animals is adapted to their 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).

Insect eyes are one of nature's most amazing creations. 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 fauna that inhabit 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 of colors. In the center of the retina are the cones of the “macula,” which are 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 darkness. 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 have visual acuity 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 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 don’t 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 popular 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 by their environment, but in many cases they can regulate it and maintain it at a higher level if necessary. 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 on this diet.

Apparently, among reptiles, only lizards have well-developed vision, since many of them hunt fast-moving prey. Aquatic reptiles rely heavily 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 torpor in frogs when, for example, a snake approaches them is a good 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 snake's quivering, forked tongue, which some people think of as a "snake's stinger," actually collects traces of various substances that quickly disappear in the air and carries them to sensitive depressions on the inside 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 extending and retracting the tongue is an effective method of sampling the air 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 the high respiratory rate leads to high 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 minimal amounts of water.

Reptile eggs contain everything necessary for a 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 the eggshell of 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 sources of heat, that is, it has simply increased the size of the inlet - the aperture. But the larger the aperture, the more blurry the image turns out (we are talking, 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 blurred 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 hardly uses multi-stage iterative mappings, but is, rather, some kind of fast one-step converter that works according to a program permanently hardwired into the nervous system.

In their work, the researchers proved that such a procedure is possible and quite realistic. They carried out mathematical modeling of how a “thermal image” occurs 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.

There was, however, an important nuance in the analysis: 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 across the entire membrane. One can only wonder how nature managed to construct such “non-local vision”, which compensates for the defects of 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 pit bottom 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 by the deep-sea inhabitants of the sea flickers there. 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. The bloodthirsty piranha in the murky waters of the Amazon, for example, perceives the water as dark red, a color more translucent than black. The water appears red due to red-colored vegetation particles that absorb visible light. Only rays of far-red light pass through the murky water and can be seen by the piranha. Infrared rays allow it to see prey, even if it hunts in complete darkness. Like piranha, crucian carp in their natural habitats often have turbid fresh water, 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 pet goldfish can see a lot more than you think, including the "invisible" infrared rays emitted by common household electronics such as the TV 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 uncanny 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 able to kill a rat with an instant blow of poisonous teeth to 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 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, reports 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 unable 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 the unique accuracy of a 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, the 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.

Bibliography

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.

A snake is an animal of the chordate type, class Reptiles, order Squamate, suborder snakes (Serpentes). Like all reptiles, they are cold-blooded animals, so their existence depends on the ambient temperature.

Snake - description, characteristics, structure. What does a snake look like?

The body of the snake has an elongated shape and can reach a length of 10 centimeters to 9 meters, and the weight of the snake ranges from 10 grams to more than 100 kilograms. Males are smaller than females, but have a longer tail. The body shape of these reptiles is varied: it can be short and thick, long and thin, and sea snakes have a flattened body that resembles a ribbon. Therefore, the internal organs of these scaly animals also have an elongated structure.

The internal organs are supported by more than 300 pairs of ribs, movably connected to the skeleton.

The snake's triangular head has jaws with elastic ligaments, which makes it possible to swallow large food.

Many snakes are venomous and use venom as a means of hunting and self-defense. Since snakes are deaf, to navigate in space, in addition to vision, they use the ability to capture vibration waves and thermal radiation.

The main information sensor is the forked tongue of the snake, which allows it to “collect information” about the environment using special receptors inside the palate. Snake eyelids are fused transparent films, scales covering the eyes, therefore snakes don't blink and even sleep with their eyes open.

The skin of snakes is covered with scales, the number and shape of which depends on the type of reptile. Once every six months, the snake sheds its old skin - this process is called molting.

By the way, the color of the snake can be either monochromatic in species living in the temperate zone, or variegated in representatives of the tropics. The pattern can be longitudinal, transversely circular or spotted.

Types of snakes, names and photographs

Today, scientists know more than 3,460 species of snakes living on the planet, among which the most famous are adders, vipers, sea snakes, snakes (not dangerous to humans), pit snakes, pseudopods with both lungs, as well as rudimentary remains of the pelvic bones and hind limbs.

Let's look at several representatives of the snake suborder:

  • King cobra (hamadryad) ( Ophiophagus hannah)

The most gigantic poisonous snake on earth. Some representatives grow up to 5.5 m, although the average size of adults usually does not exceed 3-4 m. King cobra venom is a lethal neurotoxin, causing death in 15 minutes. The scientific name of the king cobra literally means “snake eater”, because it is the only species whose representatives feed on snakes of their own kind. Females have an exceptional maternal instinct, constantly guarding the clutch of eggs and completely going without food for up to 3 months. The king cobra lives in the tropical forests of India, the Philippines and the islands of Indonesia. Life expectancy is more than 30 years.

  • Black Mamba ( Dendroaspis polylepis)

The African venomous snake, growing up to 3 m, is one of the fastest snakes, capable of moving at a speed of 11 km/h. The highly toxic snake venom causes death in a matter of minutes, although the black mamba is not aggressive and attacks humans only in self-defense. Representatives of the black mamba species received their name due to the black coloration of the oral cavity. The snake's skin is usually olive, green or brown in color with a metallic sheen. It eats small rodents, birds and bats.

  • Fierce snake (desert taipan) ( Oxyuranus microlepidotus)

The most poisonous of land snakes, the venom of which is 180 times stronger than that of a cobra. This species of snake is common in the deserts and dry plains of Australia. Representatives of the species reach a length of 2.5 m. The color of the skin changes depending on the season: in extreme heat it is straw-colored, when it gets colder it becomes dark brown.

  • Gaboon viper (cassava) ( Bitis gabonica)

The poisonous snake that lives in the African savannas is one of the largest and thickest vipers, up to 2 m long and with a body girth of almost 0.5 m. All individuals belonging to this species have a characteristic, triangular head with small horns located between the nostrils . The Gaboon viper has a calm character, rarely attacking people. It belongs to the type of viviparous snakes, breeds once every 2-3 years, bringing from 24 to 60 offspring.

  • Anaconda ( Eunectes murinus)

The giant (ordinary, green) anaconda belongs to the subfamily of boas; in former times the snake was called a water boa. The massive body, 5 to 11 m long, can weigh over 100 kg. The non-venomous reptile is found in low-flow rivers, lakes and creeks of the tropical part of South America, from Venezuela to the island of Trinidad. It feeds on iguanas, caimans, waterfowl and fish.

  • Python ( Pythonidae)

A representative of the family of non-venomous snakes, it is distinguished by its gigantic size, ranging from 1 to 7.5 m in length, and female pythons are much larger and more powerful than males. The range extends throughout the eastern hemisphere: tropical forests, swamps and savannas of the African continent, Australia and Asia. The diet of pythons consists of small and medium-sized mammals. Adults swallow leopards, jackals and porcupines whole, and then digest them for a long time. Female pythons lay eggs and incubate the clutch, by contracting muscles, increasing the temperature in the nest by 15 -17 degrees.

  • African egg snakes (egg eaters) ( Dasypeltis scabra)

Representatives of the snake family that feed exclusively on bird eggs. They live in savannas and woodlands of the equatorial part of the African continent. Individuals of both sexes grow no more than 1 meter in length. The movable bones of the snake's skull make it possible to open its mouth wide and swallow very large eggs. In this case, the elongated cervical vertebrae pass through the esophagus and, like a can opener, rip open the eggshell, after which the contents flow into the stomach, and the shell is coughed up.

  • Radiant snake ( Xenopeltis unicolor)

Non-venomous snakes, the length of which in rare cases reaches 1 m. The reptile received its name for the rainbow tint of its scales, which are dark brown in color. Burrowing snakes live in the loose soils of forests, cultivated fields and gardens in Indonesia, Borneo, the Philippines, Laos, Thailand, Vietnam and China. Small rodents and lizards are used as food items.

  • Worm-like blind snake ( Typhlops vermicularis)

Small snakes, up to 38 cm long, resemble earthworms in appearance. Absolutely harmless representatives can be found under stones, melons and watermelons, as well as in thickets of bushes and on dry rocky slopes. They feed on beetles, caterpillars, ants and their larvae. The distribution area extends from the Balkan Peninsula to the Caucasus, Central Asia and Afghanistan. Russian representatives of this species of snake live in Dagestan.

Where do snakes live?

The distribution range of snakes does not include only Antarctica, New Zealand and the islands of Ireland. Many of them live in tropical latitudes. In nature, snakes live in forests, steppes, swamps, hot deserts and even in the ocean. Reptiles lead an active lifestyle both during the day and at night. Species living in temperate latitudes hibernate in winter.

What do snakes eat in nature?

Almost all snakes are predators, with the exception of the Mexican herbivorous snake. Reptiles may only eat a few times a year. Some snakes feed on large and small rodents or amphibians, while others prefer bird eggs. The diet of sea snakes includes fish. There is even a snake that eats snakes: the king cobra can eat members of its own family. All snakes easily move on any surface, bending their body in waves; they can swim and “fly” from tree to tree, contracting their muscles.

Breeding snakes. How do snakes reproduce?

Despite the fact that snakes are solitary individuals by way of life, during the mating period they become quite sociable and “loving.” The mating dance of two snakes of different sexes is sometimes so surprising and interesting that it definitely captivates attention. The male snake is ready to hover around his “chosen one” for hours, seeking her consent to fertilization. Reptiles of the snake order are oviparous, and some snakes are capable of giving birth to live young. The size of a snake's clutch varies from 10 to 120,000 eggs, depending on the type of snake and its habitat.

Having reached sexual maturity at two years of age, snakes begin to mate. The male searches for his “lady” by smell, wraps his body around the female’s neck, rising high above the surface of the earth. By the way, at this time even non-poisonous individuals can be very aggressive due to excitement and excitement.

Mating of snakes occurs in a ball, but immediately after this the pair disperses and never meet again. The snake's parents do not show any interest in newborn babies.

The snake tries to make its clutch in the most secluded place possible: plant roots, crevices in stones, rotten stumps - every quiet corner is important for the future “mother”. The laid eggs develop quite quickly - in just one and a half to two months. Newly born snakes and baby snakes are absolutely independent, poisonous individuals have poison, but these babies can only hunt small insects. Reptiles reach sexual maturity in the second year of life. The average lifespan of a snake reaches 30 years.

What is snake venom? This is saliva produced by the salivary glands of poisonous individuals. Its healing properties have been known for hundreds of years: with the addition of snake venom, pharmacists make homeopathic preparations, creams, ointments and balms. These remedies help with rheumatic joint diseases and osteochondrosis. However, encountering a poisonous bite from this reptile in nature can be not only unpleasant and very painful, but also deadly.

What to do if bitten by a snake? First aid

  • If you have been bitten by a snake, and you do not know whether it was poisonous or non-poisonous, in any case, you should remove the snake’s saliva from the micro-wound! You can suck out and quickly spit out the poison, you can squeeze it out, but all these manipulations will be effective only for the first one to one and a half minutes after the bite.
  • The person who has been bitten definitely needs to be urgently taken to a medical facility (hospital).
  • At the same time, it is advisable to visually remember what the snake looked like, because its belonging to a certain species is most important for doctors who will prescribe anti-snake serum to the victim.
  • If a limb (arm, leg) is bitten, there is no need to tighten it: this manipulation does not localize the spread of snake venom, but may well lead to toxic asphyxia of the affected tissues.
  • Never panic! An increased heart rate due to excitement accelerates blood circulation throughout the body, thereby facilitating the spread of snake venom throughout the body.
  • Provide the bitten person with absolute rest, warm fluids, and take him to professional medical professionals as soon as possible.


Scientists have been observing the behavior of snakes for quite some time. The main organs for reading information are thermal sensitivity and smell.

The sense of smell is the main organ. The snake constantly works with its forked tongue, taking samples of air, soil, water and objects surrounding the snake.

Thermal sensitivity. A unique sensory organ that snakes have. allows you to “see” mammals while hunting even in complete darkness. In the viper, these are sensory receptors located in deep grooves on the muzzle. A snake like a rattlesnake has two large spots on its head. The rattlesnake not only sees warm-blooded prey, it knows the distance to it and the direction of movement.
The snake's eyes are covered with completely fused transparent eyelids. Vision varies among snake species, but serves primarily to track the movement of prey.

All this is interesting, but what about hearing?

It is absolutely known that snakes do not have hearing organs in the usual sense. The eardrum, auditory ossicles and cochlea, which transmit sound through nerve fibers to the brain, are completely absent.


However, snakes can hear, or rather feel, the presence of other animals. The sensation is transmitted through vibrations of the soil. This is how reptiles hunt and hide from danger. This ability to perceive danger is called vibration sensitivity. The vibration of the snake is felt throughout the body. Even very low sound frequencies are transmitted to the snake through vibration.

Quite recently, a sensational article appeared by zoologists from the Danish University of Aarhus (Aarhus University, Denmark) who studied the effect on the neurons of the python’s brain from a speaker turned on in the air. It turned out that the basics of hearing are present in the experimental python: there is an inner and outer ear, but there is no eardrum - the signal is transmitted directly to the skull. It was even possible to record the frequencies “heard” by the python bones: 80-160 Hz. This is an extremely narrow low-frequency range. Man is known to hear 16-20000 Hz. However, whether other snakes have similar abilities is not yet known.

There are about three thousand snakes on earth. They belong to the scaly order and like to live in places with warm climates. 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 ancient 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. Most species are completely harmless. Poisonous reptiles 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. Non-venomous species 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.

Of all the many different animals living on Earth, the eyes of a snake are capable of distinguishing colors and shades. Vision for a snake plays a big role in life, although it is not the main sense for familiarizing itself with the outside world. Snakes on our planet are about . As many people know from school, snakes belong to the order of squamates. Their habitat is areas with a warm or temperate climate. .

How do snake eyes work?

The snake eye, unlike other animals, does not have visual acuity. This is because their eyes are covered with a thin leathery film, they are very cloudy, and this greatly affects visibility. During molting, the snake sheds its old skin, and along with it the film. Therefore, after molting, snakes are especially “big-eyed”. Their vision becomes sharper and clearer for several months. Because of the film on the eyes, people since ancient times have given the snake's gaze a special coldness and hypnotic power.

Most snakes living near humans are harmless and do not pose any danger to humans. But there are also poisonous ones. Snake venom is used for hunting and protection.

Depending on the way of hunting - in the daytime or at night, the shape of the pupil of snakes changes. For example, the pupil is round, and snakes that engage in twilight hunting have acquired vertical and elongated eyes with long slits.

But the most unusual eyes have the species of whip snakes. Their eye is very similar to a keyhole located horizontally. Because of this unusual structure of the eyes, the snake skillfully uses its binocular vision - that is, each eye forms a complete picture of the world.

But the main sense organ of snakes is still smell. This organ is the main one for thermolocation of vipers and pythons. The sense of smell allows one to sense the warmth of its victims in pitch darkness and quite accurately determine their location. Snakes that are non-venomous strangle or wrap their bodies around their prey, and there are also those that swallow their prey alive. Most snakes are small in size, no more than one meter. During a hunt, the snake's eyes focus on one point, and their forked tongue, thanks to the Jacobson's organ, tracks the subtlest odors in the air.