Vision in insects. Compounded eyes: how do they differ from simple eyes? How does a fly see the world around him?

It is believed that a person receives up to 90% of knowledge about the outside world with the help of his stereoscopic vision. Hares have acquired lateral vision, thanks to which they can see objects located to the side and even behind them. In deep-sea fish, the eyes can occupy up to half of the head, and the parietal “third eye” of the lamprey allows it to navigate well in the water. Snakes can only see a moving object, but the eyes of the peregrine falcon are recognized as the most vigilant in the world, capable of tracking down prey from a height of 8 km!

But how do representatives of the most numerous and diverse class of living beings on Earth - insects - see the world? Along with vertebrates, to which they are inferior only in body size, it is insects that have the most advanced vision and complex optical systems of the eye. Although the compound eyes of insects do not have accommodation, as a result of which they can be called myopic, they, unlike humans, are able to distinguish extremely fast moving objects. And thanks to the ordered structure of their photoreceptors, many of them have a real “sixth sense” - polarization vision.

Vision fades - my strength,
Two invisible diamond spears...

A. Tarkovsky (1983)

It's hard to overestimate the importance Sveta (electromagnetic radiation visible spectrum) for all inhabitants of our planet. Sunlight serves as the main source of energy for photosynthetic plants and bacteria, and, indirectly through them, for all living organisms of the earth's biosphere. Light directly affects the flow of all diversity life processes animals, from reproduction to seasonal color changes. And, of course, thanks to the perception of light by special sense organs, animals receive significant (and often b O most) of the information about the world around them, they can distinguish the shape and color of objects, determine the movement of bodies, orient themselves in space, etc.

Vision is especially important for animals capable of actively moving in space: it was with the emergence of mobile animals that vision began to form and improve. visual apparatus- the most complex of all known sensory systems. These animals include vertebrates and among invertebrates - cephalopods and insects. It is these groups of organisms that can boast of the most complex organs of vision.

However, the visual apparatus of these groups differs significantly, as does the perception of images. It is believed that insects in general are more primitive compared to vertebrates, not to mention their highest level - mammals, and, naturally, humans. But how different are their visual perceptions? In other words, is the world seen through the eyes of a small creature called a fly much different from ours?

Mosaic of hexagons

The visual system of insects is, in principle, no different from that of other animals and consists of peripheral organs of vision, nerve structures and formations of the central nervous system. But as for the morphology of the visual organs, here the differences are simply striking.

Everyone is familiar with complex faceted insect eyes, which are found in adult insects or in insect larvae developing with incomplete transformation, i.e. without the pupal stage. There are not many exceptions to this rule: these are fleas (order Siphonaptera), fanwings (order Strepsiptera), most silverfish (family Lepismatidae) and the entire class of cryptognathans (Entognatha).

The compound eye looks like the basket of a ripe sunflower: it consists of a set of facets ( ommatidia) - autonomous light radiation receivers that have everything necessary to regulate the light flux and image formation. The number of facets varies greatly: from several in bristletails (order Thysanura) to 30 thousand in dragonflies (order Aeshna). Surprisingly, the number of ommatidia can vary even within one systematic group: for example, a number of species of ground beetles that live in open spaces have well-developed compound eyes with a large number ommatidia, while in ground beetles that live under stones, the eyes are greatly reduced and consist of a small number of ommatidia.

The upper layer of ommatidia is represented by the cornea (lens) - a section of transparent cuticle secreted by special cells, which is a kind of hexagonal biconvex lens. Under the cornea of most insects there is a transparent crystalline cone, the structure of which may vary between different types. In some species, especially those that are nocturnal, there are additional structures in the light-refracting apparatus that play mainly the role of anti-reflective coating and increasing light transmission of the eye.

The image formed by the lens and crystal cone falls on photosensitive retinal(visual) cells, which are a neuron with a short tail-axon. Several retinal cells form a single cylindrical bundle - retinula. Inside each such cell, on the side facing inward, the ommatidium is located rhabdomer- a special formation of many (up to 75–100 thousand) microscopic villi tubes, the membrane of which contains visual pigment. As in all vertebrates, this pigment is rhodopsin- complex colored protein. Due to the huge area of these membranes, the photoreceptor neuron contains large number rhodopsin molecules (for example, in fruit flies Drosophila this number exceeds 100 million!).

Rhabdomeres of all visual cells, combined into rhabdom, and are photosensitive, receptor elements of the compound eye, and all the retinula together constitute an analogue of our retina.

The light-refracting and light-sensitive apparatus of the facet is surrounded along the perimeter by cells with pigments that play the role of light insulation: thanks to them, the light flux, when refracted, reaches the neurons of only one ommatidia. But this is how the facets are arranged in the so-called photopic eyes adapted to bright daylight.

For species leading a twilight or nocturnal lifestyle, eyes of a different type are characteristic - scotopic. Such eyes have a number of adaptations to insufficient light flux, for example, very large rhabdomeres. In addition, in the ommatidia of such eyes, light-isolating pigments can freely migrate within the cells, due to which the light flux can reach the visual cells of neighboring ommatidia. This phenomenon underlies the so-called dark adaptation insect eyes - increased sensitivity of the eye in low light.

When rhabdomeres absorb photons of light, nerve impulses are generated in retinal cells, which are sent along axons to the paired optic lobes of the insect brain. Each optic lobe has three associative centers, where the flow of visual information simultaneously coming from many facets is processed.

From one to thirty

According to ancient legends, people once had a “third eye” responsible for extrasensory perception. There is no evidence for this, but the same lamprey and other animals, such as the tufted lizard and some amphibians, have unusual light-sensitive organs in the “wrong” place. And in this sense, insects do not lag behind vertebrates: in addition to the usual compound eyes, they have small additional ocelli - ocelli located on the frontoparietal surface, and stemms- on the sides of the head.

Ocelli are found mainly in well-flying insects: adults (in species with complete metamorphosis) and larvae (in species with incomplete metamorphosis). As a rule, these are three ocelli arranged in the form of a triangle, but sometimes the middle one or two lateral ones may be missing. The structure of ocelli is similar to ommatidia: under a light-refracting lens they have a layer of transparent cells (analogous to a crystalline cone) and a retinal retina.

Stemmas can be found in insect larvae that develop with complete metamorphosis. Their number and location varies depending on the species: on each side of the head there can be from one to thirty ocelli. In caterpillars, six ocelli are more common, arranged so that each of them has a separate field of vision.

In different orders of insects, stemma may differ from each other in structure. These differences are possibly due to their origin from different morphological structures. Thus, the number of neurons in one eye can range from several units to several thousand. Naturally, this affects the insects’ perception of the surrounding world: if some of them can only see the movement of light and dark spots, then others are able to recognize the size, shape and color of objects.

As we see, both stemmas and ommatidia are analogues of single facets, albeit modified. However, insects have other “backup” options. Thus, some larvae (especially from the order Diptera) are able to recognize light even with completely shaded eyes using photosensitive cells located on the surface of the body. And some species of butterflies have so-called genital photoreceptors.

All such photoreceptor zones are structured in a similar way and represent a cluster of several neurons under a transparent (or translucent) cuticle. Due to such additional “eyes,” dipteran larvae avoid open spaces, and female butterflies use them when laying eggs in shaded areas.

Faceted Polaroid

What can the complex eyes of insects do? As is known, any optical radiation can have three characteristics: brightness, spectrum(wavelength) and polarization(orientation of oscillations of the electromagnetic component).

Insects use the spectral characteristics of light to register and recognize objects in the surrounding world. Almost all of them are capable of perceiving light in the range from 300–700 nm, including the ultraviolet part of the spectrum, inaccessible to vertebrates.

As a rule, different colors perceived various areas compound eye insects Such “local” sensitivity can vary even within the same species, depending on the sex of the individual. Often, the same ommatidia may contain different color receptors. So, in butterflies of the genus Papilio two photoreceptors have a visual pigment with an absorption maximum at 360, 400 or 460 nm, two more at 520 nm, and the rest between 520 and 600 nm (Kelber et al., 2001).

But this is not all that the insect eye can do. As mentioned above, in visual neurons, the photoreceptor membrane of the rhabdomeral microvilli is folded into a tube of circular or hexagonal cross-section. Due to this, some rhodopsin molecules do not participate in light absorption due to the fact that the dipole moments of these molecules are located parallel to the path of the light beam (Govardovsky and Gribakin, 1975). As a result, the microvillus acquires dichroism- the ability to absorb light differently depending on its polarization. The increase in the polarization sensitivity of the ommatidium is also facilitated by the fact that the molecules of the visual pigment are not randomly located in the membrane, as in humans, but are oriented in one direction, and, moreover, are rigidly fixed.

If the eye is able to distinguish between two light sources based on their spectral characteristics, regardless of the intensity of the radiation, we can talk about color vision . But if he does this by fixing the polarization angle, as in this case, we have every reason to talk about polarization vision of insects.

How do insects perceive polarized light? Based on the structure of the ommatidium, it can be assumed that all photoreceptors must be simultaneously sensitive to both a certain length(s) of light waves and the degree of polarization of light. But in this case there may be serious problems- the so-called false color perception. Thus, light reflected from the glossy surface of leaves or water surface is partially polarized. In this case, the brain, analyzing photoreceptor data, may make a mistake in assessing the color intensity or shape of the reflective surface.

Insects have learned to successfully cope with such difficulties. Thus, in a number of insects (primarily flies and bees), a rhabdom is formed in ommatidia that perceive only color closed type, in which rhabdomeres do not contact each other. At the same time, they also have ommatidia with the usual straight rhabdoms, which are also sensitive to polarized light. In bees, such facets are located along the edge of the eye (Wehner and Bernard, 1993). In some butterflies, distortions in color perception are eliminated due to significant curvature of the microvilli of the rhabdomeres (Kelber et al., 2001).

In many other insects, especially Lepidoptera, the usual straight rhabdoms are retained in all ommatidia, so their photoreceptors are capable of simultaneously perceiving both “colored” and polarized light. Moreover, each of these receptors is sensitive only to a certain polarization angle of preference and a certain wavelength of light. This complex visual perception assists butterflies in feeding and oviposition (Kelber et al., 2001).

Unfamiliar Land

You can delve endlessly into the features of the morphology and biochemistry of the insect eye and still find it difficult to answer such a simple and at the same time incredibly complex question: how do insects see?

It is difficult for a person to even imagine the images that arise in the brain of insects. But it should be noted that it is popular today mosaic theory of vision, according to which the insect sees the image in the form of a kind of puzzle of hexagons, does not entirely accurately reflect the essence of the problem. The fact is that although each single facet captures a separate image, which is only part of the whole picture, these images can overlap with images obtained from neighboring facets. Therefore, the image of the world obtained using the huge eye of a dragonfly, consisting of thousands of miniature facet cameras, and the “modest” six-faceted eye of an ant will be very different.

Regarding visual acuity (resolution, i.e., the ability to distinguish the degree of dismemberment of objects), then in insects it is determined by the number of facets per unit convex surface eyes, i.e. their angular density. Unlike humans, insect eyes do not have accommodation: the radius of curvature of the light-conducting lens does not change. In this sense, insects can be called myopic: they see more details the closer they are to the object of observation.

At the same time, insects with compound eyes are able to distinguish very fast moving objects, which is explained by their high contrast and low inertia visual system. For example, a person can distinguish only about twenty flashes per second, but a bee can distinguish ten times more! This property is vital for fast-flying insects that need to make decisions in flight.

The color images perceived by insects can also be much more complex and unusual than ours. For example, a flower that appears white to us often hides in its petals many pigments that can reflect ultraviolet light. And in the eyes of pollinating insects, it sparkles with many colorful shades - pointers on the way to nectar.

It is believed that insects “do not see” the color red, which in “ pure form"and is extremely rare in nature (with the exception of tropical plants pollinated by hummingbirds). However, flowers colored red often contain other pigments that can reflect short-wave radiation. And if you consider that many insects are capable of perceiving not three primary colors, like a person, but more (sometimes up to five!), then their visual images should be simply an extravaganza of colors.

And finally, the “sixth sense” of insects is polarization vision. With its help, insects manage to see in the world around them what humans can only get a faint idea of using special optical filters. In this way, insects can accurately determine the location of the sun in a cloudy sky and use polarized light as a “celestial compass.” And aquatic insects in flight detect bodies of water by partially polarized light reflected from the water surface (Schwind, 1991). But what kind of images they “see” is simply impossible for a person to imagine...

Anyone who, for one reason or another, is interested in the vision of insects may have a question: why have they not developed a chamber eye similar to to the human eye, with a pupil, lens and other devices?

This question was once answered exhaustively by the outstanding American theoretical physicist, Nobel laureate R. Feynman: “Several rather interesting reasons prevent this. First of all, the bee is too small: if it had an eye similar to ours, but correspondingly smaller, then the size of the pupil would be on the order of 30 microns, and therefore the diffraction would be so great that the bee would still not be able to see better. Too much small eye- this is not very good. If such an eye is made of sufficient size, then it should be no smaller than the head of the bee itself. The value of a compound eye lies in the fact that it takes up practically no space - just a thin layer on the surface of the head. So before you give advice to a bee, don't forget that it has its own problems!

Therefore, it is not surprising that insects have chosen their own path in visual cognition of the world. Yes, and in order to see it from the point of view of insects, we would have to acquire huge compound eyes in order to maintain our usual visual acuity. It is unlikely that such an acquisition would be useful to us from an evolutionary point of view. To each his own!

Literature
1. Tyshchenko V. P. Physiology of insects. M.: graduate School, 1986, 304 p.
2. Klowden M. J. Physiological Systems in Insects. Academ Press, 2007. 688 p.
3. Nation J. L. Insect Physiology and Biochemistry. Second Edition: CRC Press, 2008.

Both flies and bees have five eyes. Three simple eyes are located in the upper part of the head (one might say, on the crown), and two complex, or facet, eyes are located on the sides of the head. The compound eyes of flies, bees (as well as butterflies, dragonflies and some other insects) are the subject of enthusiastic study by scientists. The fact is that these organs of vision are arranged in a very interesting way. They are made up of thousands of individual hexagons, or, in other words, scientific language, facets. Each of the facets is a miniature peephole that gives an image of a separate part of the object. The housefly's compound eyes have approximately 4,000 facets, worker bee- 5000, for a drone - 8000, for a butterfly - up to 17,000, for a dragonfly - up to 30,000. It turns out that the eyes of insects send to their brain several thousand images of individual parts of an object, which, although they merge into an image of the object as a whole, but all this object looks like it was made of a mosaic.

Why are compound eyes needed? It is believed that with their help insects orient themselves in flight. While simple eyes are designed to look at objects that are nearby. So, if a bee's compound eyes are removed or covered, it behaves as if it were blind. If the simple eyes are sealed, then it seems that the insect has a slow reaction.

1,2 -Compound (compound) eyes of a bee or fly
3 -three simple eyes of a bee or fly

Five eyes allow insects to cover 360 degrees, that is, to see everything that happens in front, on both sides and behind. Maybe that’s why it’s so difficult to get close to a fly unnoticed. And if you consider that compound eyes see a moving object much better than a stationary one, then one can only wonder how a person sometimes manages to swat a fly with a newspaper!

The ability of insects with compound eyes to capture even the slightest movement is reflected in the following example: if bees and flies sit down with people to watch a movie, it will seem to them that bipedal viewers are looking at one frame for a long time before moving on to look at the next. In order for insects to watch a movie (and not individual frames, like a photo), the projector film needs to be spun 10 times faster.

Should we envy the eyes of insects? Probably not. For example, the eyes of a fly see a lot, but are not capable of looking closely. That's why they discover food (a drop of jam, for example) by crawling across the table and literally bumping into it. And bees, due to the peculiarities of their vision, do not distinguish the color red - for them it is black, gray or blue.

During the evolution of vision, some animals develop rather complex optical devices. These, of course, include compound eyes. They were formed in insects and crustaceans, some arthropods and invertebrates. How is it different? compound eye from simple, what are its main functions? We'll talk about this in our material today.

Compounded eyes

This is an optical system, raster, where there is no single retina. And all the receptors are combined into small retinula (groups), forming a convex layer that no longer contains any nerve endings. Thus, the eye consists of many individual units - ommatidia, united into common system vision.

Compounded eyes, inherent in them, differ from binocular ones (inherent in humans as well) in their poor definition of small details. But they are able to distinguish between light fluctuations (up to 300 Hz), while for humans the maximum capabilities are 50 Hz. And the membrane of this type of eye has a tubular structure. In view of this, facet eyes do not have such refractive features as farsightedness or myopia; the concept of accommodation is not applicable to them.

Some structural and vision features

In many insects, they occupy most of the head and are virtually motionless. For example, the compound eyes of a dragonfly consist of 30,000 particles, forming complex structure. Butterflies have 17,000 ommatidia, flies have 4 thousand, bees have 5. The worker ant has the smallest number of particles - 100 pieces.

Binocular or facet?

The first type of vision allows you to perceive the volume of objects, their small details, estimate the distance to objects and their location in relation to each other. However, humans are limited to an angle of 45 degrees. If a more complete review is needed, eyeball carries out movement at the reflex level (or we turn our head around the axis). Compounded eyes in the form of hemispheres with ommatidia allow you to see the surrounding reality from all sides without turning your visual organs or head. Moreover, the image that the eye conveys is very similar to a mosaic: one structural unit the eyes perceive a separate element, and together they are responsible for recreating the complete picture.

Varieties

Ommatidia have anatomical features, as a result of which their optical properties differ (for example, among different insects). Scientists define three types of facet:

By the way, some types of insects have mixed type facet organs of vision, and many, in addition to those we are considering, also have simple eyes. So, in a fly, for example, on the sides of the head there are paired facet organs located quite large sizes. And on the crown there are three simple eyes that perform auxiliary functions. The bee has the same organization of visual organs - that is, only five eyes!

In some crustaceans, compound eyes seem to sit on movable stalks.

And some amphibians and fish also have an additional (parietal) eye, which distinguishes light, but has object vision. Its retina consists only of cells and receptors.

Modern scientific developments

IN lately Compounded eyes are a subject of study and delight for scientists. After all, such organs of vision, due to their original structure, provide the basis for scientific inventions and research in the world of modern optics. The main advantages are a wide overview of space, the development of artificial facets, used mainly in miniature, compact, secret surveillance systems.

SENSE ORGANS IN INSECTS

The sense organs of insects are intermediaries between external environment and the body. In accordance with external stimuli, or irritants, insects perform certain actions that make up their behavior.

The sense organs of insects are mechanical sense, hearing, chemical sense, hydrothermal sense and vision.

The basis of the sense organs is made up of nervous sensory units - sensilla. They consist of two components: a receptive structure in the skin and adjacent nerve cells. Sensilla protrude above the surface of the skin in the form of hairs, bristles, and cones (Fig. 7).

Mechanical feeling. Represented by mechanoreceptors. These are receptors, as well as sensitive structures that perceive shock, body position, its balance, etc. Tactile, or tactile, receptors are scattered throughout the body in the form of simple sensilla with sensory, i.e. sensitive hair. A change in the position of the hair upon contact with objects or air is transmitted to the sensitive cell, where excitation occurs, transmitted along its processes to the nerve center.

Mechanoreceptors also include bell-shaped sensilla. They lack sensitive hairs and are embedded in the skin. Their receptor surface in the form of a cuticular cap is located on the surface of the cuticle. The rod process of the sensitive cell - the pin - approaches the cap from below. Bell-shaped sensilla are found on the wings, cerci, legs, and tentacles. They perceive body shocks, bending, and tension.

Mechanoreceptors also include chordotonal organs as organs of hearing. Their neurons end in a rod-shaped pin. This is a series of special sensilla stretched between two sections of the cuticle. Chordotonal sensilla are called scolopophores and consist of three cells: sensory neuron, cap and parietal cells.

Not all insects have developed hearing. Orthoptera (grasshoppers, locusts, crickets), singing cicadas, some bugs and a number of lepidopterans have auditory receptors - tympanic organs. These insects chirp or sing. Tympanic organs are a collection of scolopophores that are associated with areas of the cuticle, which are presented as eardrum(Fig. 8).

In locusts, the tympanal organs are located on the sides of the 1st abdominal segment, in grasshoppers and crickets - on the tibia of the front legs (Fig. 9).

In mosquitoes, the function of the hearing organ is performed by the Johnston's organ. On the cerci of cockroaches and Orthoptera and on the body of caterpillars, neurons are located on hairs that detect sound waves.

The importance of the hearing organs:

– signals coming from individuals of their own species are perceived, which ensures a connection between the sexes, i.e. this is one of the forms of sexual signal location;

- pick up other sounds (whistles, sharp sounds, searching for a victim).

Chemical feeling. Serves to perceive the chemistry of the environment, namely taste and smell. Presented by chemoreceptors. The sense of smell perceives and analyzes a gaseous medium with a low concentration of a substance, and taste – a liquid medium with a high concentration. Chemoreceptor sensilla are presented in the form of hairs, plates or cones immersed in the body. On the antennae, the olfactory function is performed by placoid and coeloconic sensilla. The sense of smell is used by insects to search for individuals of the opposite sex, to recognize individuals of their own species, to find food and places for laying eggs. Many insects secrete attractive substances - sexual attractants or epagons.

Taste serves only to recognize food. Insects distinguish 4 main tastes - sweet, bitter, sour and salty.

Most sugars, such as glucose, fructose, maltose and others, attract bees and flies even at relatively low concentrations; other sugars, such as galactose, mannose and others, are recognized only at high concentrations, and the bees reject them. Some butterflies are very sensitive to sugars, distinguished from clean water sugar solution with a negligible concentration - 0.0027%.

Many other substances - acids, salts, amino acids, oils and others - can be rejected at high concentrations, but sometimes weak solutions Some acids and salts have an attractive effect.

Taste buds are located primarily on the mouth, but other locations are possible. So, in a bee, some flies and a number of daytime butterflies, they are located on the paws of their feet and are found high sensitivity; when the plantar side of the legs touches the sugar solution, the hungry butterfly reacts by unfolding its proboscis. Finally, in bees and folded wasps (Vespidae), these receptors are also found on the terminal segments of the antennae.

The high degree of development of the chemical sense in insects is an essential aspect of their physiology and serves scientific basis when researching and applying certain methods of chemical control of harmful species. In the practice of pest control, the bait method is used, the essence of which is that certain attracting food substances are treated with poisons and distributed in places where the pest is concentrated; Such poisoned baits are widely and very successfully used in the fight against locusts. In the fight against pests, attractive substances, or attractants, are also sought.

Hygrothermic feeling. It is essential in the life of a number of insects and, depending on humidity conditions and environmental temperature, regulates the behavior of the individual; it also controls water balance and body temperature. The corresponding receptors have not been studied enough, but it has been established that the sensation of moisture is localized in some insects on the head and its appendages - antennae and tentacles, and the sensation of warmth - on the antennae, paws and other organs. The perception of heat is highly developed in insects, and individual species have their own optimal temperature zone to which they strive. However, the boundaries of the temperature optimum depend on the temperature and humidity conditions of the environment in which the insect developed, as well as on the phase of its development.

Vision. Together with chemical sense, it probably plays a decisive role in the life of insects. The organs of vision have a complex structure and are represented by two types of eyes: complex and simple (Fig. 10).

Rice. 10. Schematic section (A) and facets on the surface (B) of a compound eye: 1 – cornea; 2 – crystal cone; 3 – retinal cells.

Compound, or facet, eyes, two of them, are located on the sides of the head, are often very developed and can then occupy a significant part of the head. Each compound eye consists of multivisual units - sensilla, which are called ommatidia; their number in a compound eye can reach many hundreds, as well as thousands.

The ommatidium consists of three types of cells, forming the somatic, sensitive and pigment parts (Fig. 11). On the outside, each ommatidium forms a round or hexagonal cell on the surface of the eye - a facet, which is why compound eyes get their name. The optical, or refractive, part of the ommatidium consists of a transparent lens and an underlying transparent crystal cone. The lens, or cornea, is essentially a transparent cuticle and usually looks like a biconvex lens. The crystal cone is formed by four elongated transparent cells and, together with the lens, forms a single optical system - a cylindrical lens; the length of its optical axis significantly exceeds its diameter. The sensitive part is located under the optical one, forms the retina, or retina, which perceives light rays, and consists of a series of retinal cells. These cells are elongated along the ommatidium, located sectorially and form the lining of its central rod - the optic rod, or rhabdom. At their base, retinal cells pass into nerve fibers, going to the visual lobes of the brain. The pigment part is formed by pigment cells, which together form the lining of the sensitive part and the crystal cone; due to this, each ommatidium is optically isolated from the neighboring one. Consequently, the pigment part performs the function of an optical isolation apparatus.

Diurnal insects have so-called appositional vision. Thanks to optical isolation using pigment cells, each ommatidium is transformed into an isolated thin tube; therefore, only rays coming through the lens and, moreover, only strictly coinciding with the longitudinal axis of the ommatidium can penetrate into it. These rays reach the optic rod, or rhabdom; the latter is precisely the perceptive element of the retina. Consequently, the field of view of each ommatidium is very small and it sees only an insignificant part of the object in question. But large number ommatidia allows you to dramatically increase the field of view by mutual application to each other or apposition; As a result, from individual smallest parts of the image, a single overall image is formed, like in a mosaic. Thus, insects have mosaic vision.

Nocturnal and twilight insects have superposition vision, which is associated with the morphological and physiological differences of their ommatidia. In the superposition eye, the sensitive part is more distant from the optical part, and pigment cells isolate mainly the optical part. Thanks to this optic rod 2 types of rays penetrate - straight and oblique; the former enter the ommatidia through the lens, and the latter from neighboring ommatidia, which enhances the light effect. Consequently, the image of an object is obtained in this case not only by combining individual perceptions, but also by superimposing them, or superposition.

In strong daylight superposition eye acquires some physiological similarities with the appositional eye. This happens because the pigment in the pigment cells begins to move in the light and is distributed so that it forms a dark tube around the ommatidium; Thanks to this, the ommatidia are almost optically isolated from each other and receive rays predominantly from their lens. This ability of the eye to respond to the degree of illumination can be considered as accommodation. To some extent, it is also characteristic of the appositional eye, which allows diurnal insects to quickly adapt the eye to vision in bright light and in the shade, for example, when flying from an open place to a forest.

With the help of compound eyes, insects distinguish shape, movement, color and distance to an object, as well as polarized light. However, the wide variety of insects, their lifestyle and habits, undoubtedly creates a variety of features of their vision. The latter depend on the structural features of the eyes and their ommatidia; diameter, length, number of latter and other properties determine the quality of vision. It is believed that many species are myopic and can only distinguish movement at a distance. This is confirmed by many experiments. Thus, dragonfly larvae rush at moving prey and do not notice stationary prey. A mesh placed in front of the wasp nest with cells exceeding the length of their body still blocks the entrance to the nest, but after some time the wasps will learn to crawl through the cells of this mesh.

Most insects are blind to the color red, but they can see ultraviolet radiation and are attracted by it; The range of visible light waves lies in the range of 2500–8000 A. The honey bee has the ability to distinguish polarized light emitted by the blue sky, which allows it to navigate in space when flying. A number of insects are also characterized by changes in movement depending on the direction of the sun's rays, i.e. Sun compass orientation. The essence of this phenomenon is that the angle of incidence of the rays on certain parts of the retina remains constant for some time; the interrupted movement is resumed at the same angle, but due to the movement of the sun, the direction of movement changes by the same number of degrees.

Closely related is the photocompass movement, which explains the arrival of nocturnal insects to the light. Light rays diverge radially and when moving obliquely in relation to them, the angle of their incidence will change; To maintain a fixed angle, the insect is forced to constantly change its path towards the light source. The movement follows a logarithmic spiral and ultimately leads the insect to the light source itself (Fig. 12).

Simple eyes, or ocelli, are located between the compound eyes on the forehead and crown, or only on the crown (Fig. 13). They are small, usually numbering three, and arranged in a triangle. Due to their position at the top of the head, they are often also called dorsal ocelli. Morphologically, the ocelli do not correspond to the ommatidia of the compound eyes. Thus, they are innervated not from the optic lobes of the brain, but from the middle part of the protocerebrum. In addition, for one optical part they have a series of sensitive parts. They also lack a crystal cone and their optical part is represented only by a cuticular lens, i.e. one lens.

Not all insects have eyes; in particular, they are absent in many dipterans and butterflies. In wingless or short-winged insects they are also absent or rudimentary. Their role is not clear enough. It has been established that in a number of forms the focus of the eye lies behind the sensitive part, therefore there cannot be image perception in this case; Painting over the compound eyes makes these insects blind. At the same time, there is an anatomical connection between the ocellar nerves and the nerves of the compound eyes, which indicates the existence functional connection between these bodies. Undoubtedly, the eyes of different insects can play a different role. In any case, for many they have a regulating effect on the compound eyes, ensuring stability of vision in conditions of fluctuating light intensity. At low intensity, the ocelli enhance the reaction of the compound eyes, i.e. become segments of the latter; at high levels, they exhibit an inhibitory effect on the compound eyes.

The lateral or lateral ocelli, characteristic of insect larvae with complete metamorphosis, should be distinguished from the dorsal ocelli. These ocelli, also called stemmas, are located on the sides of the head in the place where compound eyes are found in adults. Their number is different and even variable within the same species. Some species have only one eye on each side, while others have six or more pairs. When an insect moves into adult state the lateral ocelli atrophy and are replaced by compound eyes.

Stemmata vary in structural details, but they are characterized by the presence of a lens. Butterfly caterpillars also have a crystal cone and only one rhabdom is developed, which makes this ocellus similar to the ommatidium of a compound eye. But in the larvae of sawflies, some beetles and other insects, several or even many rhabdoms are present in the eye, and the crystal cone may be absent. This makes such stemmata similar not to ommatidia, but to dorsal ocelli.

The lateral ocelli are innervated from the optic lobes of the brain and their visual function is indisputable.

Some insects retain the ability to respond to light when the eyes and ocelli are removed or covered with black varnish; cockroaches avoid light, as in in good condition, and the caterpillars maintain a positive reaction and move towards the light source. Eyeless cave insects can also respond to light. Obviously, the surface of their body is capable of sensing light and therefore we can talk about cutaneous photosensitivity.

Ability to see the world around us in the entire spectrum of its colors and shades - unique gift nature to man. The world of colors that our eyes can perceive is bright and amazing. But man is not the only living creature on this planet. Do animals and insects also see objects, colors, night shapes? How do flies or bees see our room, for example, or a flower?

insect eyes

Modern science, with the help of special instruments, has been able to see the world through the eyes of different animals. This discovery became a sensation in its time. It turns out that many of our smaller brothers, and especially insects, see a completely different picture from the one we see. Do flies even see? Yes, but not at all like that, and it turns out that we and flies, and other flying and crawling ones, seem to live in the same world, but completely different.

It's all about Insects, he is not alone, or rather, not entirely alone. The eye of an insect is a collection of thousands of facets or ommatidia. They look like cone lenses. Each such ommatidia sees a different part of the picture, accessible only to it. How do flies see? The image they observe looks like a picture assembled from a mosaic, or a puzzle.

The visual acuity of insects depends on the number of ommatidia. The most sighted is the dragonfly, it has an ommatidia - about 30 thousand. Butterflies are also sighted - about 17 thousand, for comparison: a fly has 4 thousand, a bee - 5. The most visually impaired is the ant, its eye contains only 100 facets.

All-round defense

Another ability of insects that differs from humans is the ability to see all around. The eye-lens is capable of seeing everything at 360 o. Among mammals, the hare has the largest visual angle - 180 degrees. That’s why he’s nicknamed the oblique one, but what to do if there are so many enemies. The lion is not afraid of enemies, and his eyes look at less than 30 degrees of the horizon. In small insects, nature compensated for the lack of growth with the ability to see everyone who creeps up on them. What else distinguishes the visual perception of insects is the speed at which the picture changes. During a fast flight, they manage to notice everything that people cannot see at such speed. For example, how do flies see TV? If our eyes were like those of a fly or a bee, we would need to spin the film ten times faster. It is almost impossible to catch a fly from behind; it sees the wave of the hand faster than it occurs. A person seems like a slow turtle to an insect, and a turtle looks like a generally motionless stone.

Rainbow colors

Almost all insects are color blind. They distinguish colors, but in their own way. It is interesting that the eyes of insects and even some mammals do not perceive red color at all or see it as blue or violet. To a bee, red flowers look black. Plants that need bee pollination do not bloom red. Most bright colors are scarlet, pink, orange, burgundy, but not red. Those rare ones that allow themselves a red outfit are pollinated in a different way. This is the relationship in nature. It’s hard to imagine how scientists managed to figure out how flies see the colors of a room, but it turns out that their favorite color is yellow, and blue and green irritate them. Just like that. To have fewer flies in your kitchen, you just need to paint it correctly.

Can flies see in the dark?

Flies, like most flying insects, sleep at night. Yes, yes, they need sleep too. If a fly is constantly driven away and not allowed to sleep for three days, it dies. Flies see poorly in the dark. These are insects with round eyes, but shortsighted. They do not need eyes to find food.

Unlike flies, worker bees see well at night, which allows them to work in night shift Same. At night, the flowers smell more intensely and there are fewer competitors for nectar.

They see well at night, but the undoubted leader in vision in the dark is the American cockroach.

Item Shape

The perception of the shape of an object by different insects is interesting. The specificity is that they may not perceive simple forms at all, which are not necessary for their viability. Bees and butterflies do not see objects of simple shapes, especially stationary ones, but they are attracted to everything that has complex flower shapes, especially if they move or sway. This explains, in particular, the fact that bees and wasps rarely sting a person standing motionless, and if they do, it is in the area of the lips when he is talking (moving his lips). Flies and some other insects do not perceive a person; they sit on him simply in search of food, which they look for by smell and see with sensors on their paws.

General features of insect vision

Only butterflies can distinguish the red color - they pollinate rare flowers of this range.
All eyes have a facet structure, the difference being in the number of ommatidia.
Trichromasia, or the ability to transform colors into three primary colors: violet, green and ultraviolet.
The ability to break and reflect light rays and see the whole picture of the surrounding reality.
The ability to look at pictures that change very quickly.
Insects can navigate by sunlight, so moths flock to the lamp.
Binocular vision helps predators in the insect world accurately determine distances to their prey.