Vision in insects. Why do insects have round eyes, like insects see? From an insect's point of view

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 4000, worker bee- 5000, for butterflies - up to 17,000, and for dragonflies - up to 30,000! Thus, the ant's vision is very mediocre, while the dragonfly's huge eyes - two iridescent hemispheres - provide the maximum field of vision.

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 They are excellent at distinguishing flickering (blinking) light with a frequency of up to 250–300 hertz (for humans, the maximum 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 more wide range illumination, and this, accordingly, reduces their sensitivity.

Many insects have complex compound eyes, consisting of numerous individual ocelli - ommatidia. Insects see the world as if it were assembled from a mosaic. Most insects are "shortsighted". Some of them, such as the diopsid fly, can be seen at a distance of 135 meters. Butterfly - and she has the most sharp vision among our insects, it does not see further than two meters, and the bee does not see anything at a distance of one meter. Insects whose eyes are made of large quantity ommatidia, are able to notice the slightest movement around them. If an object changes its position in space, then its reflection in the compound eyes also changes its location, moving by a certain number of ommatidia, and the insect notices this. Compound eyes play a huge role in the life of predatory insects. Thanks to this structure of the visual organs, the insect can focus its eyes on the desired object or observe it only with part of the compound eye. Interestingly, moths navigate using vision and always fly towards a light source. The azimuth of their eyes in relation to moonlight always less than 90°.

Color vision

In order to see a certain color, the insect's eye must perceive electromagnetic waves a certain length. Insects perceive well both ultrashort and ultralong light waves and colors of the visible spectrum by the human eye. It is known that a person sees colors from red to violet, but his eye is not able to perceive ultraviolet radiation- waves that are longer than red and shorter than purple. Insects see ultraviolet light, but do not distinguish the colors of the red spectrum (only butterflies see red). For example, a poppy flower is perceived by insects as colorless, but on other eye colors, insects see ultraviolet patterns that are even difficult for humans to imagine. Insects navigate these patterns in search of nectar. Butterflies also have ultraviolet patterns on their wings that are invisible to humans. Bees recognize the following colors: bluish-green, violet, yellow, blue, bee purple and ultraviolet. Insects are also able to navigate using polarized light. When passing through the Earth's atmosphere, a ray of light is refracted, and as a result of the polarization of light, different areas the sky has different wavelengths. Thanks to this, even when the sun is not visible because of the clouds, the insect accurately determines the direction.

Interesting facts

The larvae of some beetles have developed simple eyes, thanks to which they see well and escape from predators. Adult beetles develop compound eyes, but their vision is no better than that of larvae. Complex compound eyes are found not only in insects, but also in some crustaceans, such as crabs and lobsters. Instead of lenses, ommatidia contain miniature mirrors. For the first time, people were able to look at the world through the eyes of an insect in 1918 thanks to the German scientist Exner. The number of small eyes in insects (depending on the species) varies from 25 to 25,000. The eyes of insects, for example, beetles that swim on the surface of the water, are divided into two parts: upper part serves to see in the air, and the lower one - under water. The compound eyes of insects do not see as well as the eyes of birds and mammals because they are unable to capture fine detail (insects can have between 25 and 25,000 facets). But they perceive moving objects well, and even register colors that are inaccessible to the human eye.

The most complex of the sense organs in insects are the organs of vision. The latter are represented by formations of several types, of which the most important are complex faceted eyes of approximately the same structure as the complex eyes of crustaceans.

The eyes consist of individual ommatidia (Fig. 337), the number of which is determined mainly by the biological characteristics of the insects. Active predators and good fliers, dragonflies have eyes with up to 28,000 facets each. At the same time, ants (Hymenoptera order), especially working individuals of species that live underground, have eyes consisting of 8 - 9 ommatidia.

Each ommatidium represents a perfect photooptic sensilla (Fig. 338). It consists of an optical apparatus, including the cornea, a transparent section of the cuticle above the ommatidium and the so-called crystal cone. Together they act as a lens. The perceptive apparatus of the ommatidia is represented by several (4 - 12) receptor cells; their specialization has gone very far, as evidenced by their complete loss of flagellar structures. The actual sensitive parts of the cells - rhabdomeres - are clusters of densely packed microvilli, located in the center of the ommatidium and closely adjacent to each other. Together they form photosensitive element eyes - rhabdom.

Shielding pigment cells lie along the edges of the ommatidium; the latter differ quite significantly between diurnal and nocturnal insects. In the first case, the pigment in the cell is motionless and constantly separates neighboring ommatidia, preventing light rays from passing from one eye to the other. In the second case, the pigment is able to move in the cells and accumulate only in their upper part. In this case, the light rays hit the sensitive cells of not one, but several neighboring ommatidia, which significantly (almost two orders of magnitude) increases the overall sensitivity of the eye. Naturally, this kind of adaptation arose in twilight and nocturnal insects. Nerve endings that form the optic nerve extend from the sensory cells of the ommatidia.

In addition to compound eyes, many insects also have simple ocelli (Fig. 339), the structure of which does not correspond to the structure of a single ommatidium. The light-refracting apparatus is lens-shaped; immediately below it is a layer of sensitive cells. The entire eye is covered with a cover of pigment cells. The optical properties of simple eyes are such that they cannot perceive images of objects.

Insect larvae in most cases have only simple ocelli, which, however, differ in structure from the simple ocelli of the adult stages. There is no continuity between the ocelli of adults and larvae. During metamorphosis, the eyes of the larvae are completely resorbed.

The visual abilities of insects are perfect. However, the structural features of the compound eye predetermine a special physiological mechanism of vision. Animals with compound eyes have “mosaic” vision. The small size of ommatidia and their isolation from each other lead to the fact that each group of sensitive cells perceives only a small and relatively narrow beam of rays. Rays incident at a significant angle are absorbed by shielding pigment cells and do not reach the photosensitive elements of the ommatidia. Thus, schematically, each ommatidia receives an image of only one small point of an object located in the field of view of the entire eye. As a result, the image is composed of as many light points corresponding to different parts of the object as the number of facets the rays from the object fall perpendicularly to. The overall picture is combined, as it were, from many small partial images by applying them one to another.

The perception of color by insects is also distinguished by a certain originality. Representatives higher groups Insecta have color vision based on the perception of three primary colors, the mixing of which gives all the colorful diversity of the world around us. However, in insects, compared to humans, there is a strong shift to the short-wave part of the spectrum: they perceive green-yellow, blue and ultraviolet rays. The latter are invisible to us. Consequently, the color perception of the world by insects is sharply different from ours.

The functions of simple eyes of adult insects still require serious study. Apparently, they to some extent “supplement” the compound eyes, influencing the activity and behavior of insects in different lighting conditions. In addition, it has been shown that simple ocelli, along with compound eyes, are capable of perceiving polarized light.

Insects, like other multicellular organisms, have many different receptors, or sensilla, sensitive to certain stimuli. Insect receptors are very diverse. Insects have mechanoreceptors ( auditory receptors, proprioceptors), photoreceptors, thermoreceptors, chemoreceptors. With their help, insects capture radiation energy in the form of heat and light, mechanical vibrations, including a wide range of sounds, mechanical pressure, gravity, concentration of water vapor in the air and volatile substances, as well as many other factors. Insects have a developed sense of smell and taste. Mechanoreceptors are trichoid sensilla that perceive tactile stimuli. Some sensilla can detect the slightest vibrations in the air around the insect, while others signal the position of body parts relative to each other. Air receptors perceive the speed and direction of air flows near the insect and regulate flight speed.

Vision

Vision plays a big role in the lives of most insects. They have three types of visual organs - compound eyes, lateral (stemmas) and dorsal (ocellie) ocelli. Diurnal and flying forms usually have 2 complex eyes and 3 ocellia. Stemmas are present in insect larvae with complete metamorphosis. They are located on the sides of the head in the amount of 1-30 on each side. The dorsal ocelli (ocellie) occur together with the compound eyes and function as additional visual organs. Ocellia are noted in the adults of most insects (absent in many butterflies and dipterans, in worker ants and blind forms) and in some larvae (stoneflies, mayflies, dragonflies). As a rule, they are found only in insects that fly well. There are usually 3 dorsal ocelli located in a triangle in the frontoparietal region of the head. Their main function is probably to estimate illumination and its changes. They are also thought to be involved in insect visual orientation and phototaxis reactions.

The visual characteristics of insects are determined by faceted structure eyes, which consist of a large number of ommatidia. Largest number ommatidia were found in butterflies (12-17 thousand) and dragonflies (10-28 thousand). The photosensitive unit of the ommatidium is the retinal (visual) cell. Photoreception of insects is based on the transformation of the visual pigment rhodopsin under the influence of a light quantum into the isomer metarhodopsin. Its reverse restoration makes it possible repetition elementary visual acts. Typically, photoreceptors contain 2-3 visual pigments that differ in their spectral sensitivity. The data set of visual pigments also determines the features color vision insects Visual images in compound eyes are formed from many point images created by individual ommatidia. Compound eyes lack the ability to accommodate and cannot adapt to vision at different distances. Therefore, insects can be called “extremely myopic.” Insects are characterized by an inversely proportional relationship between the distance to the object in question and the number of details discernible by their eye: the closer the object is, the more details they see. Insects are able to judge the shape of objects, but at short distances from them, this requires that the outlines of the objects fit into the field of view of the compound eye.

Insect color vision can be dichromatic (ants, bronze beetles) or trichromatic (bees and some butterflies). At least one species of butterfly has tetrachromatic vision. There are insects that are able to distinguish colors with only one (upper or lower) half of the compound eye (four-spotted dragonfly). For some insects, the visible part of the spectrum is shifted to shorter wavelengths. For example, bees and ants do not see red color (650-700 nm), but they distinguish part of the ultraviolet spectrum (300-400 nm). Bees and other pollinating insects can see ultraviolet patterns on flowers that are hidden from human vision. Similarly, butterflies are able to distinguish elements of wing coloration that are visible only in ultraviolet radiation.

The perception of sounds transmitted through a solid substrate is carried out in insects by vibration receptors located in the shins of the legs near their articulation with the thigh. Many insects have high sensitivity to shaking of the substrate on which they are located. The perception of sounds through air or water is carried out by phonoreceptors. Diptera perceive sounds using Johnston organs. The most complex auditory organs of insects are the tympanic organs. The number of sensilla included in one tympanic organ varies from 3 (some butterflies) to 70 (locusts) and even up to 1500 (in song cicadas). In grasshoppers, crickets and mole crickets, the tympanic organs are located in the tibia of the front legs, in locusts - on the sides of the first abdominal segment. Auditory organs Song cicadas are located at the base of the abdomen in the vicinity of the sound-producing apparatus. The auditory organs of moths are located in the last thoracic segment or in one of the two anterior abdominal segments and can perceive ultrasound emitted bats. Honeybees produce sounds by vibrating part of the thorax through frequent muscle contractions. The sound is amplified by the wing plates. Unlike many insects, bees are able to produce sounds of different pitches and timbres, which allows them to transmit information through different characteristics sound.

Vision

Insects have a developed olfactory apparatus. The perception of odors is carried out thanks to chemoreceptors - olfactory sensilla located on the antennae, and sometimes on the perioral appendages. At the level of chemoreceptors, the primary separation of olfactory stimuli occurs due to the presence of two types of receptor neurons. Generalist neurons recognize a very wide range of chemical compounds, but at the same time have low sensitivity to odors. Specialist neurons respond only to one or a few related chemical compounds. They provide perception odorous substances, triggering certain behavioral reactions (sex pheromones, food attractants and repellents, carbon dioxide). In male silkworms, the olfactory sensilla reach a theoretically possible limit of sensitivity: just one molecule of the female pheromone is enough to excite a specialist neuron. In his experiments, J. A. Fabre determined that males of the pear peacock eye can detect females by pheromones at a distance of up to 10 km.

Contact chemoreceptors form peripheral section insect taste analyzer and allow them to evaluate the suitability of the substrate for feeding or oviposition. These receptors are located on the mouth parts, tips of the legs, antennae and ovipositor. Most insects are able to recognize solutions of salts, glucose, sucrose and other carbohydrates, as well as water. Insect chemoreceptors rarely respond to artificial substances that mimic sweet or bitter tastes, unlike vertebrate chemoreceptors. For example, saccharin is not perceived by insects as a sweet substance.

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 does a compound eye differ from a simple eye, what are its main functions? We'll talk about this in our material today.

Compounded eyes

This optical system, raster, where there is no single retina. And all the receptors are combined into small retinules (groups), forming a convex layer that does not contain any more 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 performing 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.