What is vision called in insects? Insect organs of vision

Insects are currently the most prosperous group of animals on Earth.

The body of insects is divided into three sections: head, thorax and abdomen.

On the head of insects there are compound eyes and four pairs of appendages. Some species have simple ocelli in addition to compound eyes. The first pair of appendages is represented by antennae (antennae), which are organs of smell. The remaining three pairs form the oral apparatus. Upper lip (labrum), unpaired fold, covers upper jaws. The second pair of oral appendages forms the upper jaws (mandibles), the third pair - mandibles(maxilla), the fourth pair fuses and forms the lower lip (labium). There may be a pair of palps on the lower jaw and lower lip. The oral apparatus includes the tongue (hypopharynx), a chitinous protrusion of the floor of the oral cavity (Fig. 3). Due to the way they feed, the mouthparts may be various types. There are gnawing, gnawing-licking, piercing-sucking, sucking and licking types of mouthparts. The primary type of oral apparatus should be considered gnawing (Fig. 1).

rice. 1.
1 - upper lip, 2 - upper jaws, 3 - lower jaws, 4 - lower lip,
5 - main segment of the lower lip, 6 - “stem” of the lower lip, 7 - mandibular palp,
8 - internal chewing blade of the lower jaw, 9 - external
chewing lobe of the lower jaw, 10 - chin,
11 - false chin, 12 - sublabial palp, 13 - uvula, 14 - accessory uvula.

The chest consists of three segments, which are called the prothorax, mesothorax and metathorax, respectively. Each of the thorax segments bears a pair of limbs; in flying species, there are a pair of wings on the mesothorax and metathorax. The limbs are articulated. The main segment of the leg is called the coxa, followed by the trochanter, femur, tibia and tarsus (Fig. 2). Due to the way of life, the limbs are walking, running, jumping, swimming, digging and grasping.

rice. 2. Structure diagram
insect limbs:
1 - wing, 2 - coxa, 3 - trochanter,
4 - thigh, 5 - lower leg, 6 - paw.

rice. 3.
1 - compound eyes, 2 - simple ocelli, 3 - brain, 4 - salivary
gland, 5 - goiter, 6 - front wing, 7 - hind wing, 8 - ovary,
9 - heart, 10 - hindgut, 11 - caudal seta (cerci),
12 - antenna, 13 - upper lip, 14 - mandibles (upper
jaws), 15 - maxilla (lower jaws), 16 - lower lip,
17 - subpharyngeal ganglion, 18 - abdominal nerve cord,
19 - midgut, 20 - Malpighian vessels.

The number of abdominal segments varies from 11 to 4. Lower insects have paired limbs on the abdomen; in higher insects they are modified into an ovipositor or other organs.

The integument is represented by the chitinous cuticle, hypodermis and basement membrane, protect insects from mechanical damage, water loss, and are an exoskeleton. Insects have many glands of hypodermal origin: salivary, odorous, poisonous, arachnoid, waxy, etc. The color of the integument of insects is determined by pigments contained in the cuticle or hypodermis.

rice. 4. Longitudinal section through
black cockroach head:
1 - mouth opening, 2 - pharynx,
3 - esophagus, 4 - brain
(suprapharyngeal ganglion),
5 - subpharyngeal nerve ganglion,
6 - aorta, 7 - salivary duct
glands, 8 - hypopharynx, or
subpharyngeal, 9 - preoral
cavity, 10 - anterior section
preoral cavity, or
cibarium, 11 - posterior section
preoral cavity,
or salivary.

Insect muscles histological structure They are classified as striated, they are distinguished by their ability to contract at a very high frequency (up to 1000 times per second).

Digestive system as in all arthropods, it is divided into three sections, the anterior and posterior sections are of ectodermal origin, the middle one is of endodermal origin (Fig. 5). The digestive system begins with the oral appendages and oral cavity, into which the ducts of 1-2 pairs of salivary glands open. The first pair of salivary glands produces digestive enzymes. The second pair of salivary glands can be modified into arachnoid or silk-secreting glands (caterpillars of many species of butterflies). The ducts of each pair unite into an unpaired canal, which opens at the base of the lower lip under the hypopharynx. The anterior section includes the pharynx, esophagus and stomach. In some species of insects, the esophagus has an extension - a goiter. In species that feed on plant foods, the stomach contains chitinous folds and teeth that facilitate the grinding of food. Middle section represented by the midgut, in which food is digested and absorbed. In its initial part, the midgut may have blind outgrowths (pyloric appendages). The pyloric appendages function as digestive glands. In many insects that feed on wood, symbiotic protozoa and bacteria settle in the intestines, secreting the enzyme cellulase and thereby facilitating the digestion of fiber. The posterior section is represented by the hindgut. At the border between the middle and posterior sections, numerous blindly closed Malpighian vessels open into the intestinal lumen. The hindgut has rectal glands that suck water from the remaining food mass.

rice. 5. Structure diagram
digestive system
black cockroach:
1 - salivary glands, 2 -
esophagus, 3 - goiter, 4 -
pyloric appendages,
5 - midgut,
6 - Malpighian vessels,
7 - hindgut,
8 - rectum.

The respiratory organs of insects are the trachea, through which gases are transported. The tracheae begin with openings - spiracles (stigmas), which are located on the sides of the mesothorax and metathorax and on each abdominal segment. The maximum number of spiracles is 10 pairs. Often stigmas have special closing valves. The trachea look like thin tubes and penetrate the entire body of the insect (Fig. 6). The terminal branches of the trachea end in a stellate tracheal cell, from which even thinner tubes extend - tracheoles. Sometimes the trachea forms small expansions - air sacs. The walls of the trachea are lined with a thin cuticle, having thickenings in the form of rings and spirals.

rice. 6. Scheme
buildings
respiratory
black systems
cockroach

Insect circulatory system - open type(Fig. 7). The heart is located in the pericardial sinus on the dorsal side of the ventral body. The heart has the appearance of a tube, blindly closed at the posterior end. The heart is divided into chambers, each chamber has paired openings with valves on the sides - ostia. The number of cameras is eight or less. Each chamber of the heart has muscles that provide its contraction. The wave of heart contractions from the posterior chamber to the anterior provides One Way blood forward.

Hemolymph moves from the heart into a single vessel - into the cephalic aorta and then pours into the body cavity. Through numerous openings, hemolymph enters the cavity of the pericardial sinus, then through the ostia, with the expansion of the cardiac chamber, it is sucked into the heart. Hemolymph has no respiratory pigments and is a yellowish liquid containing phagocytes. Its main function is to supply the organs with nutrients and transfer metabolic products to the excretory organs. Respiratory function hemolymph is insignificant; only in some aquatic insect larvae (larvae of bell-bellied mosquitoes) the hemolymph has hemoglobin, is colored bright red and is responsible for the transport of gases.

The excretory organs of insects are the Malpighian vessels and the fat body. Malpighian vessels (up to 150 in number) are of ectodermal origin, flow into the intestinal lumen at the border between the middle and posterior sections intestines. The excretion product is uric acid crystals. The fatty body of insects, in addition to its main function - storing reserves nutrients, also serves as a “storage bud”. The fat body contains special excretory cells that are gradually saturated with sparingly soluble uric acid.

rice. 7. Structure diagram
circulatory system
black cockroach:
1 - heart, 2 - aorta.

The central nervous system of insects consists of paired suprapharyngeal ganglia (brain), subpharyngeal ganglia and segmental ganglia of the ventral nerve cord. The brain includes three sections: protocerebrum, deutocerebrum and tritocerebrum. The protocerebrum innervates the acron and the eyes located on it. Mushroom-shaped bodies develop on the protocerebrum, to which nerves from the visual organs approach. The deutocerebrum innervates the antennae, and the tritocerebrum innervates the upper lip.

The abdominal nerve chain includes 11-13 pairs of ganglia: 3 thoracic and 8-10 abdominal. In some insects, the thoracic and abdominal segmental ganglia merge to form the thoracic and abdominal ganglia.

The peripheral nervous system is represented by nerves extending from the central nervous system, and sense organs. There are neurosecretory cells, the neurohormones of which regulate the activity of the endocrine organs of insects.

The more complex the behavior of insects, the more developed their brain and mushroom bodies are.

The sensory organs of insects reach a high degree of perfection. The capabilities of their sensory apparatus often exceed those of higher vertebrates and humans.

The organs of vision are represented by simple and with complicated eyes(Fig. 8). Compound or compound eyes are located on the sides of the head and consist of ommatidia, the number of which in different insect species varies from 8-9 (ants) to 28,000 (dragonflies). Many insect species have color vision. Each ommatidia perceives a small part of the visual field of the entire eye, the image is composed of many small particles of the image, such vision is sometimes called “mosaic”. The role of simple ocelli has not been fully studied; it has been established that they perceive polarized light.

rice. 8.
A - compound eye (ommatidia are visible on the section), B - diagram
structure of an individual ommatidium, B - diagram of the structure of a simple
eyes: 1 - lens, 2 - crystal cone, 3 - pigment
cells, 4 - visual (retinal) cells,
5 - rhabdom (optic rod), 6 - facets (external
surface of the lens), 7 - nerve fibers.

Many insects are capable of making sounds and hearing them. The hearing organs and organs that produce sounds can be located in any part of the body. For example, in grasshoppers, the hearing organs (tympanal organs) are located on the shins of the front legs; there are two narrow longitudinal slits leading to eardrum related to receptor cells. The organs that produce sounds are located on the front wings, with the left wing corresponding to the “bow” and the right wing to the “violin”.

The olfactory organs are represented by a set of olfactory sensilla located mainly on the antennae. The antennae of males are more developed than those of females. By smell, insects search for food, places for laying eggs, and individuals of the opposite sex. Females secrete special substances - sexual attractants that attract males. Male butterflies find females at a distance of 3-9 km.

Taste sensilla are located on the jaw and labial palps of beetles, on the legs of bees, flies, and butterflies, and on the antennae of bees and ants.

Tactile receptors, thermo- and hygroreceptors are scattered over the surface of the body, but most of them are on the antennae and palps. Many insects perceive magnetic fields and their changes; where the organs that perceive these fields are located is still unknown.

Insects are dioecious animals. Many insect species exhibit sexual dimorphism. The male reproductive system includes: paired testes and vas deferens, unpaired ejaculatory duct, copulatory organ and accessory glands. The copulatory organ includes cuticular elements - the genitals. The accessory glands secrete a secretion that dilutes the sperm and forms the spermatophore membrane. The female reproductive system includes: paired ovary and oviducts, unpaired vagina, spermatic receptacle, accessory glands. Females of some species have an ovipositor. The genitalia of males and females have a complex structure and taxonomic significance.

Insects reproduce sexually; parthenogenesis (aphids) is known for a number of species.

The development of insects is divided into two periods - embryonic, including the development of the embryo in the egg, and postembryonic, which begins from the moment the larva emerges from the egg and ends with the death of the insect. Postembryonic development occurs with metamorphosis. Based on the nature of metamorphosis, these arthropods are divided into two groups: insects with incomplete transformation (hemimetabolous) and insects with complete transformation (holometabolous).

In hemimetabolous insects, the larva is similar to the adult animal. It differs from it in its underdeveloped wings - gonads, the absence of secondary sexual characteristics, and its smaller size. Such imago-like larvae are called nymphs. The larva grows, molts, and after each molt the wing rudiments enlarge. After several molts, the older nymph emerges as an adult.

In holometabolous insects, the larva is not similar to the imago not only in structure, but also ecologically; for example, the larva of the cockchafer lives in the soil, while the imago lives in trees. After several molts, the larvae turn into pupae. During the pupal stage, the larval organs are destroyed and the body of an adult insect is formed.

rice. 9.
A - open (rider), B -
covered (butterfly),
B - hidden (fly).

The larvae of holometabolous insects do not have complex eyes or wing rudiments. Their mouthparts are of the gnawing type, and their antennae and limbs are short. According to the degree of development of the limbs, four types of larvae are distinguished: protopod, oligopod, polypod, apod. Protopod larvae have only rudiments chest legs(bees). Oligopod larvae have three pairs of normal walking legs (beetles, lacewings). Polypod larvae, in addition to three pairs of thoracic legs, have several more pairs of false legs on the abdomen (butterflies, sawflies). The abdominal legs are projections of the body wall, bearing spines and hooks on the sole. Apodal larvae do not have limbs (diptera).

According to the methods of movement, the larvae of holometabolous insects are divided into campodeoid, eruciform, wireworm and vermiform.

Campodeoid larvae have a long flexible body, running legs and sensory cerci (ground beetles). Eruciform larvae are a fleshy, slightly curved body with or without limbs (chafer beetles, bronze beetles, dung beetles). Wireworms - with a rigid body, round in diameter, with supporting cerci (click beetles, darkling beetles). Vermiformes - by appearance worm-like, legless (diptera and many others).

Pupae are of three types: free, covered, hidden (Fig. 9). In free pupae, the rudiments of wings and limbs are clearly visible, freely separated from the body, the integument is thin and soft (beetles). In covered pupae, the rudiments grow tightly to the body, the integument is highly sclerotized (butterflies). Hidden pupae are free pupae located inside a false cocoon - puparia (flies). The puparia is an unshed hardened larval skin.

Question "How many eyes does a common fly have?" is not as simple as it seems. Two big eyes located on the sides of the head can be seen with the naked eye. But in reality, the structure of the fly's visual organs is much more complex.

If you look at a magnified view of a fly's eyes, you can see that they are honeycomb-like and made up of many individual segments. Each part has the shape of a hexagon with regular edges. This is where the name for this eye structure comes from – facet (“facette” translated from French means “edge”). Many arthropods can boast of complex faceted eyes, and the fly is far from holding the record for the number of facets: it has only 4,000 facets, while dragonflies have about 30,000.

The cells we see are called ommatidia. Ommatidia have a cone-shaped shape, the narrow end of which extends deep into the eye. The cone consists of a cell that perceives light and a lens protected by a transparent cornea. All ommatidia are closely pressed to each other and connected by the cornea. Each of them sees “their” fragment of the picture, and the brain puts these tiny images into one whole.

The arrangement of the large compound eyes is different in female and male flies. In males, the eyes are set close together, while in females they are more spaced apart, since they have a forehead. If you look at a fly under a microscope, then in the middle of the head above the facet organs of vision you can see three small dots arranged in a triangle. In fact, these points are simple eyes.

In total, the fly has one pair of compound eyes and three simple ones - five in total. Why did nature take such a difficult path? The fact is that facet vision was formed in order to primarily cover as much space as possible with the gaze and capture movement. Such eyes perform basic functions. With simple eyes, the fly was “provided” to measure the level of illumination. Compound eyes are the main organ of vision, and simple eyes are a secondary organ. If a fly did not have simple eyes, it would be slower and could only fly in bright light, and without compound eyes it would go blind.

How does a fly see the world around it?

Large, convex eyes allow the fly to see everything around it, that is, the visual angle is 360 degrees. This is twice as wide as a human's. The insect's motionless eyes simultaneously look in all four directions. But the visual acuity of a fly is almost 100 times lower than that of a human!

Since each ommatidia is an independent cell, the picture turns out to be a mesh, consisting of thousands of individual small images that complement each other. Therefore, for a fly, the world is an assembled puzzle consisting of several thousand pieces, and a rather vague one at that. The insect sees more or less clearly at only a distance of 40 - 70 centimeters.

The fly is able to distinguish colors and even invisible to the human eye polarized light and ultraviolet. The fly's eye senses the slightest changes in the brightness of light. She is able to see the sun hidden by thick clouds. But in the dark, flies see poorly and lead a predominantly diurnal lifestyle.

Another interesting ability of a fly is its quick reaction to movement. A fly perceives a moving object 10 times faster than a human. It easily “calculates” the speed of an object. This ability is vital for determining the distance to the source of danger and is achieved by “transmitting” the image from one cell - the ommatidia - to another. Aviation engineers took advantage of this feature of the fly's vision and developed a device for calculating the speed of a flying aircraft, repeating the structure of its eye.

Thanks to such fast perception, flies live in a slower reality compared to us. A movement that lasts a second, from a human point of view, is perceived by a fly as a ten-second action. Surely people seem to them to be very slow creatures. The insect's brain works at the speed of a supercomputer, receiving an image, analyzing it and transmitting the appropriate commands to the body in thousandths of a second. Therefore, it is not always possible to swat a fly.

So, the correct answer to the question “How many eyes does an ordinary fly have?” the number will be five. The main ones are a paired organ in the fly, as in many living beings. Why nature created exactly three simple eyes remains a mystery.

From an insect's point of view

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 largest and most diverse class of living creatures 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” - polarized 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 entire variety of life processes of animals, from reproduction to seasonal color changes. And, of course, thanks to the perception of light by special sensory organs, animals receive a significant (and often most) part 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 the visual apparatus began to form and improve - 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 form an image. The number of facets varies greatly: from a few 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 living in open spaces have well-developed compound eyes with a large number of ommatidia, while ground beetles living under stones have greatly reduced eyes 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.

Species that lead a twilight or nocturnal lifestyle are characterized by eyes of a different type - 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 light photons in retinal cells, nerve impulses, 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: while some of them can only see the movement of light and dark spots, 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 places.

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.

Typically, different colors are perceived by different areas of an insect's compound eye. 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 of 360, 400 or 460 nm, two more - 520 nm, and the rest - from 520 to 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 removed 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 helps butterflies when feeding and laying eggs (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 difficult 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 of convex surface of the eye, 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 the high contrast and low inertia of their 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 its “pure form” 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 did they not develop a chamber eye, similar 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: “This is hindered somewhat interesting reasons. 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. An eye that is too small is not a good thing. 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. 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

Tyshchenko V. P. Physiology of insects. M.: graduate School, 1986, 304 S.

Klowden M. J. Physiological Systems in Insects. Academ Press, 2007. 688 p.

Nation J. L. Insect Physiology and Biochemistry. Second Edition: CRC Press, 2008.

Even in distant childhood, many of us asked such seemingly trivial questions about insects, such as: how many eyes does an ordinary fly have, why a spider weaves a web, and why a wasp can bite.

The science of entomology has answers to almost any of them, but today we will call on the knowledge of researchers of nature and behavior in order to understand the question of what the visual system of this species is.

In this article we will analyze how a fly sees and why this annoying insect is so difficult to swat with a fly swatter or to catch with your palm on a wall.

Room dweller

The housefly or housefly belongs to the family of true flies. And even though the topic of our review concerns all species without exception, for convenience we will allow ourselves to consider the entire family using the example of this very familiar species of domestic parasites.

The common house fly is a very unremarkable insect in appearance. It has a grey-black body coloration, with some hints of yellow on the lower abdomen. The length of an adult individual rarely exceeds 1 cm. The insect has two pairs of wings and compound eyes.

Compound eyes - what's the point?

The fly's visual system includes two large eyes located at the edges of the head. Each of them has a complex structure and consists of many small hexagonal facets, hence the name of this type of vision as faceted.

In total, the fly eye has more than 3.5 thousand of these microscopic components in its structure. And each of them is capable of capturing only a tiny part of the overall image, transmitting information about the resulting mini-picture to the brain, which puts all the puzzles of this picture together.

If you compare facet vision and binocular vision, which a person has, for example, you can quickly see that the purpose and properties of each are diametrically opposed.

More developed animals tend to concentrate their vision on a certain narrow area or on specific object. For insects, it is important not so much to see a specific object as to quickly navigate in space and notice the approach of danger.

Why is she so difficult to catch?

This pest is really very difficult to take by surprise. The reason is not only the increased reaction of the insect in comparison with a slow person and the ability to take off almost instantly. Mainly, such a high level of reaction is due to the timely perception by the brain of this insect of changes and movements within the viewing radius of its eyes.

A fly's vision allows it to see almost 360 degrees. This type of vision is also called panoramic. That is, each eye provides a 180-degree view. It is almost impossible to take this pest by surprise, even if you approach it from behind. The eyes of this insect allow you to control the entire space around it, thereby providing one hundred percent all-round visual defense.

There is another interesting feature of the fly’s visual perception of the color palette. After all, almost all species perceive differently certain colors familiar to our eyes. Some of them cannot be distinguished by insects at all, others look different to them, in different colors.

By the way, in addition to two compound eyes, the fly has three more simple eyes. They are located in the space between the facets, on the frontal area of ​​the head. Unlike compound eyes, these three are used by insects to recognize an object in the immediate vicinity.

Thus, to the question of how many eyes does an ordinary fly have, we can now safely answer – 5. Two complex facet eyes, divided into thousands of ommatidia (facets) and designed for the most extensive control over changes in the environment around it, and three simple eyes , allowing, as they say, sharpening.

View of the world

We have already said that flies are colorblind, and they either do not distinguish all colors, or they see objects familiar to us in other color tones. This species is also able to distinguish ultraviolet light.

It should also be said that, despite the uniqueness of their vision, these pests practically cannot see in the dark. At night, the fly sleeps because its eyes do not allow this insect to hunt in the dark.

And these pests also tend to perceive well only smaller and moving objects. An insect cannot distinguish objects as large as a person, for example. For a fly, it is nothing more than another part of the interior of the environment.

But the approach of a hand to an insect is perfectly detected by its eyes and promptly gives the necessary signal to the brain. Just like seeing any other rapidly approaching danger, it will not be difficult for these sneakers, thanks to the complex and reliable tracking system that nature has provided them with.

Conclusion

So we analyzed what the world looks like through the eyes of a fly. We now know that these ubiquitous pests have, like all insects, amazing visual apparatus, allowing them not to lose vigilance, and during daylight hours to maintain a circular observation defense at one hundred percent.

The vision of a common fly resembles a complex tracking system, including thousands of mini-surveillance cameras, each of which provides the insect with timely information about what is happening in the immediate range.

The functions of the chordotonal organs appear to be different. In cases where the sensilla are adjacent to the cuticle, they, as a rule, serve to perceive low-frequency vibrations. True, in some cases (chordotonal organs located in the antennae of mosquitoes) they are also sensitive to high-frequency vibrations. Internal chordotonal organs probably record changes in pressure and mechanical stress occurring in the insect's body.

The true auditory organs of insects are the tympanic organs, in which the scolpophores are associated with thin cuticular membranes (tympanic membranes), which act as eardrums.

The tympanal organs of grasshoppers, located on the shins of the front legs, have a typical structure. In the upper part of the tibia there are two narrow longitudinal slits leading into two tympanic pockets. Inner walls The pockets facing each other are thin and represent eardrums, while the outer ones are thickened and are called tympanic operculum. Between both eardrums, closely adjacent to them, there are two tracheal trunks, which, perhaps, serve as resonators. Finally, the main part of the tympanic organ consists of three groups of scolpophores. The scolpophores are partly adjacent to the tympanic membrane and partly to the resonating trachea. The central processes of sensory cells form the tympanic nerve. Exactly the same principle - a combination of scolpophores and tympanic membranes - is used to structure the tympanic organs of other insects - locusts, crickets, butterflies, etc. True, they can be located in different places of the body - on the anterior segments of the abdomen, at the base of the wings, etc.

Chordotonal sensilla of the tympanic organs serve to perceive vibrations of different frequencies - there are “high-frequency” and “low-frequency” sensilla. As a rule, one of these groups is tuned to the frequencies that are most represented in the sounds produced by individuals of the same species. In general, insects perceive sounds in a very wide range: from infrasound (8-10 Hz) to ultrasound (45000 Hz).

Insects are capable of not only perceiving, but also making sounds. This feature is characteristic of representatives of many groups: Orthoptera, beetles, Hymenoptera, butterflies, etc. Sound organs insects are very diverse.

The chirping of Orthoptera, for example, is caused by the development of the well-known chirping adaptations, which are most often associated with the wings. So, in grasshoppers these organs are located on the front wings. Some veins of the left wing become jagged and turn into a so-called bow, which the animal moves along the right wing, where a resonator is located in the corresponding place. The latter consists of a platform on the wing limited by a high vein - a mirror. The movement of the jagged bow along the edge of the mirror leads to vibration of the part of the wing surface stretched on it.

In locusts, the bow is formed by a row of tiny denticles on the thighs hind legs. When the thighs rub against the upper wings, the denticles touch the radial vein of the wing, which is very prominent in the male. Male cicadas have a peculiar " voice apparatus"on bottom side metathorax: its action is based on extremely rapid vibration of the chitinous membrane, driven by muscle contraction. The significance of the ability to make sounds lies, apparently, in attracting females by chirping males.

Insect chemoreceptors are represented by olfactory and gustatory sensilla. The cuticular formations of the olfactory sensilla are very diverse in shape: bristles, cone-shaped appendages, plates, etc. General feature- the presence of thin pores penetrating the cuticle. Through these pores, access to the sensitive elements of the sensilla is open for molecules of odorous substances. The olfactory sensilla are located mainly on the palps and maxillary palps.

Insects use their sense of smell both to find food and when mating: males often find females by smell. The latter highlight special odorous substances- sexual attractants. A tiny amount (100 molecules per 1 cm 3 of air) of such a substance is enough to cause excitement in male silkworms.

Taste sensilla are located in insects on the oral limbs and distal segments of the legs. Their cuticular elements are represented by hairs or cone-shaped appendages and are also riddled with pores. Each sensilla includes several receptor cells, each of which reacts to a specific taste stimulus: one cell reacts to salts, another to sugary substances, the third to clean water. One of the sensory cells of the taste sensilla is mechanoreceptor. Thus, in insects, as well as in vertebrates, the sense of taste is accompanied by the sense of touch.

The most complex of the sense organs in insects are 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, the number of which is determined mainly biological features 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. 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 the photosensitive element of the eye - the 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. Ommatidia originate from sensory cells nerve endings forming the optic nerve.

In addition to compound eyes, many insects also have simple eyes, 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.

Visual abilities of insects 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 of 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 “supplement” the compound eyes to some extent, influencing the behavioral activity 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.

In addition to the listed sense organs, insects also have a number of receptor apparatuses. These are the sensilla that perceive the temperature of the environment and its humidity. Aquatic insects are able to detect changes in pressure, etc.

Respiratory organs. For breathing, a complexly developed tracheal system is used. On the sides of the body there are up to 10 pairs, sometimes fewer, of spiracles, or stigmas: they lie on the mesothorax and metathorax and on 8 abdominal segments.

Stigmas are often equipped with special closing devices and each lead into a short transverse canal, and all transverse canals are connected to each other by a pair (or more) of the main longitudinal tracheal trunks. Thinner tracheas originate from the trunks, branching repeatedly and entangling all the organs with their branches. Each trachea ends in a terminal cell with radiating processes pierced by the terminal tubules of the trachea. The terminal branches of this cell (tracheoles) even penetrate into individual cells of the body. Sometimes the trachea forms local expansions, or air sacs, which serve in terrestrial insects to improve air ventilation in the tracheal system, and in aquatic insects, probably as reservoirs that increase the supply of air in the animal’s body. Tracheas appear in insect embryos in the form of deep invaginations of the ectoderm; like other ectodermal formations, they are lined with cuticle. IN surface layer the latter forms a spiral thickening, which gives the trachea elasticity and prevents the walls from collapsing.

In the simplest cases, the entry of oxygen into the tracheal system and the removal of carbon dioxide from it occurs by diffusion through constantly open stigmas. This is observed, however, only in inactive insects living in conditions of high humidity.