The organs of vision are developed in most insects. The greatest development is achieved compound or compound eyes . The number of visual elements - ommatidia, or facets, in the eye of a housefly reaches 4 thousand, and in dragonflies even 28 thousand. The ommatidia consists of a transparent lens, or cornea, in the form of a biconvex lens and an underlying transparent crystal cone. Together they make up optical system. Under the cone is the retina, which perceives light rays. The cells of the retina are connected by nerve fibers to the optic lobes of the brain. Each ommatidium is surrounded by pigment cells.
Depending on the perception of light of varying intensities, appositional and superpositional types of eyes are distinguished. The first type of eye structure is characteristic of diurnal insects, the second - nocturnal.
IN apposition eye each ommatidia is isolated in its upper part by pigment from neighboring ommatidia. Thus, each structural unit of the eye works separately from all the others, perceiving only “its” part external space. The overall picture is formed in the insect’s brain as if from many pieces of a mosaic.
IN superposition eye Ommatidia are only partially, albeit along their entire length, protected from lateral rays: they are semi-permeable. On the one hand, this interferes with insects in intense light, on the other hand, it helps them see better in the twilight.
Ocellus (dorsal simple eyes) - these are small organs of vision that are present in some adults and are usually located on the top of the head. Usually presented in the amount of three, with one lying slightly in front, and two more - behind and to the side of the front. They do not contain ommatidium, and the structure of simple ocelli is significantly simplified. Outside is the cornea, consisting of corneagenic cells, deeper is the light-receiving apparatus made of retinal (sensitive) cells, and even lower are pigment cells that pass into the fibers of the optic nerve.
Of all the types of insect eyes, simple ocelli have the weakest ability to see. According to some reports, they do not perform at all visual function, and are only responsible for improving the function of the compound eyes. This, in particular, is proven by the fact that insects practically do not have simple eyes in the absence of complex ones. Moreover, when painting compound eyes insects cease to navigate in space, even if they have well-defined simple eyes.
Stemmas, or lateral simple eyes– present in insect larvae with complete metamorphosis. During the pupal stage, they "morph" into compound eyes. They perform a visual function, but, due to their simplified structure, they see relatively poorly. To improve vision, larval eyes are often present in several pieces. In sawfly larvae they are similar to the dorsal ones, and in butterfly caterpillars they resemble the ommatidia of the compound eye. Caterpillars perceive the shape of objects and distinguish small details on their surface.
Insect eye high magnification looks like a fine lattice.
This is because the insect's eye is made up of many small "eyes" called facets. The eyes of insects are called faceted. The tiny facet eye is called ommatidium. The ommatidium has the appearance of a long narrow cone, the base of which is a lens shaped like a hexagon. Hence the name compound eye: facette translated from French means "edge".
A tuft of ommatidia makes up the complex, round, insect eye.
Each ommatidia has a very limited field of view: the visual angle of ommatidia in the central part of the eye is only about 1°, and at the edges of the eye - up to 3°. The ommatidium “sees” only that tiny section of the object in front of its eyes at which it is “aimed”, that is, where the extension of its axis is directed. But since the ommatidia are closely adjacent to each other, and their axes are in round eye diverge radially, then the entire compound eye covers the object as a whole. Moreover, the image of the object turns out to be mosaic, that is, made up of separate pieces.
The number of ommatidia in the eye varies from insect to insect. A worker ant has only about 100 ommatidia in its eye, a housefly has about 4,000, a worker bee has 5,000, butterflies have up to 17,000, and dragonflies have up to 30,000! Thus, an ant has very mediocre vision, while huge eyes dragonflies - two iridescent hemispheres - provide maximum field of view.
Due to the fact that the optical axes of ommatidia diverge at angles of 1-6°, the clarity of the image of insects is not very high: they do not distinguish small details. In addition, most insects are myopic: they see surrounding objects at a distance of only a few meters. But compound eyes are excellent at distinguishing flickering (blinking) light with a frequency of up to 250–300 hertz (for humans, the limiting frequency is about 50 hertz). The eyes of insects are able to determine the intensity of the light flux (brightness), and in addition, they have a unique ability: they can determine the plane of polarization of light. This ability helps them navigate when the sun is not visible in the sky.
Insects distinguish colors, but not at all like we do. For example, bees “do not know” the color red and do not distinguish it from black, but they perceive invisible to us ultraviolet rays, which are located at the opposite end of the spectrum. Ultraviolet radiation is also detected by some butterflies, ants and other insects. By the way, it is the blindness of pollinating insects to the red color that explains the curious fact that among our wild flora there are no plants with scarlet flowers.
Light coming from the sun is not polarized, that is, its photons have an arbitrary orientation. However, when passing through the atmosphere, light is polarized as a result of scattering by air molecules, and the plane of its polarization is always directed towards the sun
By the way...
In addition to compound eyes, insects have three more simple ocelli with a diameter of 0.03-0.5 mm, which are located in the form of a triangle on the fronto-parietal surface of the head. These eyes are not suitable for distinguishing objects and are needed for a completely different purpose. They measure the average level of illumination, which is used as a reference point (“zero signal”) when processing visual signals. If you seal these eyes of an insect, it retains the ability to spatially orientate itself, but will only be able to fly in brighter light than usual. The reason for this is that sealed eyes are mistaken for “ intermediate level» black field and thereby give the compound eyes a wider range of illumination, and this, accordingly, reduces their sensitivity.
The brain of a fly is hardly larger than the hole in a sewing needle. But a fly, having such a brain, manages to process more than a hundred static images (frames) per second. As you know, the human limit is approximately 25 frames per second. And the fly found a simpler and effective way image processing. And this could not but interest researchers in the field of robotics.
Flies were found to process 100 frames per second. And this allows them to detect an obstacle during flight within a few milliseconds (a millisecond is one thousandth of a second). In particular, the researchers focused their attention on optical flows, which they called "optical field flows." It appears that this optical field is processed only by the first layer of neurons. They process the “rough” source signal from each fly “pixel”. And they send the processed information to the next layer of neurons. And, according to the researchers, there are only 60 of these secondary neurons in each hemisphere of the fly brain. However, the fly brain manages to reduce or fragment the field of view into many sequential “motion vectors” that give the fly a vector of direction of movement and “instantaneous” speed. And what’s interesting is that the fly sees it all!
We, people (and not everyone), know what a vector and instantaneous speed are. And the fly, naturally, has no idea about these things. And such abilities of the fly’s brain to process a huge amount of information can only be envied. Why do we see only about 50 frames per second, and the fly 100? It's hard to say, but there are reasonable guesses on this matter. How does a fly fly? Almost “instantly”, with enormous acceleration. We could hardly withstand such an overload. But it is possible to create a robotic brain that is as fast as the brain of a fly in processing information flows.
To try to understand how a tiny fly brain can process such a huge amount of information, researchers in Munich have created a “flight simulator” for a fly. The fly could fly, but was kept on a leash. Electrodes recorded the response of the fly's brain cells. And researchers tried to understand what happens in the fly’s brain during flight.
The first results are obvious. Flies process images from their fixed eyes very differently than humans do. When a fly moves in space, “optical flux fields” are formed in its brain, which give the fly the direction of movement.
How would a person see it? For example, when moving forward, surrounding objects would instantly scatter to the sides. And objects in the field of view would appear larger than they actually are. And it would seem that nearby and distant objects move differently.
The speed and direction with which objects flash before the eyes of a fly generate typical patterns of motion vectors - field flows. Which, at the second stage of image processing, reach the so-called “lobula plate” - the center of vision more high level. In each hemisphere of the fly's brain there are only 60 nerve cells responsible for vision. Each of these nerve cells responds only to a signal with a certain intensity.
But for the analysis of optical flows, information coming from both eyes simultaneously is important. This connection is provided by special neurons called “VS cells”. They allow the fly to accurately assess its location in space and flight speed. It appears that the “VS cells” are responsible for sensing and responding to the torque applied to the fly during its flight maneuvers.
Robotics researchers are working to develop robots that can observe environment with the help digital cameras, study what they see and respond appropriately to changes in the current situation. And communicate and interact with people effectively and safely.
For example, development is already underway on a small flying robot, the position and speed of which will be controlled using a computer system that imitates the vision of a fly.
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Varieties of the structure of the organs of vision
In insects, eyes can be presented in three varieties:
- (faceted);
- (dorsal, ocelli);
- larval (lateral, larval). (photo)
They have different structure and unequal ability to see.
Compound eyes are found in most insects, and the more highly developed the latter are, the better their visual organs are usually developed. They are also called facet lenses, because their outer surface is represented by a set of lenses located next to each other - facets.
Ommatidium
Ommatidium
A (left) - appositional ommatidium,
B (right) - superposition ommatidium
1 - axons of visual cells, 2 - retinal cells,
3 - cornea, 4 - crystalline cone,
5 - pigment cells, 6 - light guide, 7 - rhabdom
The compound eye consists of various, usually large quantity individual structural units - ommatidia. include a number of structures that provide conduction, refraction of light (facet, corneal cells, crystalline cone) and perception of visual signals (retinal cells, rhabdom, nerve cells). In addition, each has a pigment insulation device, due to which it is fully or partially protected from side rays.
Diagram of the structure of a simple eye
Of all types of eyes, insects have the weakest ability to see. According to some reports, they do not perform a visual function at all, and are only responsible for improving the function of the compound eyes. This, in particular, is proven by the fact that in insects there are practically no simple ones without complex ones. In addition, when the compound eyes are painted over, insects cease to orient themselves in space, even if they have well-defined eyes.
Features of insect vision
A huge number of scientific works are devoted to the study of insect vision. Due to such interest on the part of specialists, many of the features of the eyes of Insecta have now been reliably clarified. However, the structure of the visual organs in these organisms is so diverse that the quality of vision, perception of color and volume, discrimination between moving and stationary objects, recognition of familiar visual images and other properties of vision vary enormously in different groups insects The following factors can influence this: in a compound eye - the structure of ommatidia and their number, convexity, location and shape of the eyes; in simple eyes and - their number and subtle structural features, which can be represented by a significant variety of options. The vision of bees has been studied best to date.
The movement of an object plays a certain role in the perception of shape. Insects are more likely to land on flowers that sway in the wind than on stationary ones. dragonflies rush after moving prey, and male butterflies react to flying females and have trouble seeing sitting ones. This is probably due to a certain frequency of irritation of the ommatidia of the eyes during movement, flickering and flickering.
Recognizing familiar objects
Insects recognize familiar objects not only by color and shape, but also by the arrangement of objects around them, so the idea of the exceptional primitiveness of their vision cannot be called true. For example, the Sand Wasp finds the entrance to a burrow, guided by the objects that are located around it (grass, stones). If they are removed or their location is changed, this can confuse the insect.
Perception of distance
This feature is best studied using the example of dragonflies, ground beetles and other predatory insects.
The ability to determine distance is due to the presence of higher insects binocular vision, that is, two eyes whose fields of vision partially intersect. The structural features of the eyes determine how large the distance available for viewing of a particular insect is. For example, jumping beetles react to prey and pounce on it when they are at a distance of 15 cm from the object.
Light-compass movement
Many insects move in such a way that they constantly maintain the same angle of incidence of light on the retina. Thus, sun rays are a kind of compass by which the insect is oriented. By the same principle, moths move in the direction of artificial light sources.
