Why do insects have round eyes like insects see? Panoramic camera "eye of the fly.

Each of us who has at least once tried to get rid of an annoying fly by running after it with a cracker in hand knows perfectly well that this task is not always easy to accomplish, and sometimes even impossible at all. The reaction of a gray-black small tenant is what you need. The fact is that you are not a competitor to her. Why? Read the article in which we will tell you all about winged annoyances.

What is superior to us this fly:

in the speed of movement (more than twenty kilometers per hour),
in the ability to keep track of her rapid movements.

How flies see

We, the representatives of the human race, who consider ourselves so perfect and omnipotent, have only binocular vision allowing you to focus on specific object or in a certain narrow area in front of us, and are in no way able to see what is happening behind us, but for a fly this is not a problem, since its vision is panoramic, it sees the entire space at 360 degrees (each eye is able to provide a view of 180 degrees).

In addition, these insects are not just due to anatomical structure of their visual apparatus they can see in different directions at once, but they are also able to purposefully survey the space around them. AND all this is provided located on the sides with two large convex eyes that stand out well on the head of the insect. Such a huge field of view determines the special "insight" of these insects. In addition, they need significantly less time to identify objects than we humans. Their visual acuity also exceeds our human 3 times.

The structure of compound eyes

If you look at the eye of a fly under a microscope, you can see that it is composed, like a mosaic, of many small sections - facets - hexagonal structural units, outwardly very similar in shape to honeycombs. Such an eye, respectively called faceted, and the facets themselves are also called ommatidia in a different way. In the eye of a fly, one can count about four thousand such facets. All of them give their image (a small part of the whole), and the brain of a fly forms from them, like from puzzles, a big picture.

panoramic, faceted vision and binocular, which is characteristic of people, have a diametrically opposite purpose. For insects to be able to quickly navigate and not only notice the approach of danger, but also to have time to avoid it, it is important not to see a specific object well and clearly, but, mainly, to carry out timely perception of movements and changes in space.

There is another interesting feature visual perception fly around the world, touching the palette of colors. Some, so familiar to our eyes, of which insects do not distinguish at all, others look different to them than to us, in other tones. As for the beauty of the surrounding space - flies distinguish not only the seven primary colors, but also their subtlest shades, because their eyes are able to see not only visible light, but also ultraviolet, which, alas, people cannot see. It turns out that in the visual perception of a fly the world more iridescent than humans.

It should also be noted that, having certain advantages of the visual system, these representatives of the six-legged world (yes, they have 3 pairs of legs) cannot see in the dark. They sleep at night because their eyes do not allow them to navigate dark time days.

And these small and nimble creatures notice only medium-sized and moving objects. An insect does not perceive such a large object, for example, as a person. And here the approach of a human hand to a fly, its eyes see perfectly and immediately transmit the necessary signal to the brain. Also, any other rapidly approaching danger will not be difficult for them to see, thanks to the complex and reliable structure of the eyes, which allows the insect to see space in all directions at the same time - right, left, up, back and forth and react accordingly, saving itself, which is why they are so difficult slap.

Numerous facets allow the fly to follow very fast moving objects with high image clarity. For comparison, if a person's vision can perceive 16 frames per second, then a fly has 250-300 frames per second. This property is necessary for flies, as already described, to catch movements from the side, as well as for their own orientation in space during a fast flight.

number of eyes in a fly

By the way, in addition to two large complex compound eyes, the fly has three more simple, located on the forehead heads in the interval between the faceted ones. In contrast to the compound eye, these three are needed in order to see objects at close range, since the compound eye in this case is useless.

Thus, when asked how many eyes a housefly has, we can now accurately answer that there are five of them:

two faceted (complex), consisting of thousands of ommatidia and necessary to obtain information about events rapidly changing in space,
and three simple eyes, allowing you to sort of sharpen.

Compound eyes are located in flies on the sides of the head, moreover, in females, the location of the organs of vision is somewhat expanded (separated by a wide forehead), while in males, the eyes are slightly closer to each other.

If we consider the eye of an insect under a strong magnifying glass, we will see that it consists of the smallest round lattice. And this seems to be for the reason that the eye of an insect consists of many small eyes, on scientific language called "facets". Today we are trying to understand why insects have round eyes, how do insects see the objects around them? These are so often interested in the child, but?

Features of the structure of the organs of vision

The eyes of insects are divided into three types:

complex (faceted);
simple;
larval.

The structure of such eyes is different, and insects are able to see them differently.

The complex structure of the eyes predominates in maximum number insects, depends on the development of the living being itself. These eyes are made up of multiple individual structural elements- ommatidians.

Through them, light is transmitted, refracted, visual signals are perceived. Each individual ommatidium is distinguished by the presence of a pigment isolation apparatus, which completely or partially protects against lateral light.

Ommatidia are divided into two main types, which affects the structural features of the eyes.

Appasial eye has isolated ommatidia. Each of them is able to work individually from the rest, seeing only certain part surrounding space. The picture is formed in the brain of an insect, like the smallest mosaic.
In the second group - superposition, ommatidia, though partially, but have protection from lateral rays. This somewhat prevents insects from seeing at light intensity, but improves vision at dusk.

Simple eyes include organs of vision that some insects have and are usually located on the top of the head.

The structure of such eyes is significantly simplified, they see weaker than others. It is believed that such eyes are completely devoid of visual ability, and are only responsible for improving the functions of compound eyes.

And if you paint over faceted insects, it will not be able to navigate in space, even having well-defined eyes of a simple structure.

Larval eyes are the organs of vision that insect larvae have, which have the ability to completely turn into compound eyes. Their structure is somewhat simplified, which does not allow the insect to see well.

Distinctive features of insect vision

Insect vision has been studied for a long time. Thanks to the increased interest of scientists, it was possible to find out a lot of distinctive features associated with the performance of the eyes.

And anyway, the building visual organs so different that the quality of image perception, color, volume, movement different groups insects is different. Several factors influence this:

compound eye is different structural structure ommatidia and number, convexity, arrangement and forms;
simple eyes and stemmas differ in the number and subtlety of the structure, having great amount options.

Eyes of insects with different numbers of ommatidia:

an ant has 6000 facets
the fly has 4000
in beetles 9000
butterflies 17000
and the most complex eye of a dragonfly has 28,000-30,000 facets.

Insects see differently: the visible beam spectrum is reduced on the left side, and increased on the right.

In a dragonfly, only the lower facets distinguish colors, the upper ones distinguish the shape. Dragonfly eyes occupy most head, so the dragonfly is able to see - feel what is happening behind her back. The dragonfly does not see the object, but feels its heat, sees in the infrared range.

Insects are able to distinguish forms, but this does not happen in the same way as in humans. Butterflies and bees ignore the circle or oval, but are attracted to the radial structure, which resembles a flower corolla. An object that is distinguished by the complexity of the figure and the play of shadows will attract attention much more quickly. It is also interesting that bees like objects that are small in size.
It is noteworthy that insects are able to "recognize" objects even by location.

Even in early childhood, many of us asked such seemingly trifling questions about insects, such as: how many eyes does common fly why a spider spins a web, and a wasp can bite.

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

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

room resident

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

The common house fly is a very unremarkable external insect. It has a gray-black coloration of the body, with some hints of yellowness in the lower part of the abdomen. Length adult 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 consists of two big eyes located along 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 facet.

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

If you compare facet vision and binocular vision, which a person has, for example, you can quickly make sure 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 a 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 hard 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 slow person and the ability to take off almost instantly. Mainly so high level The reaction is due to the timely perception of the brain of this insect of changes and movements within the viewing radius of its eyes.

The fly's vision allows it to see almost 360 degrees. This type of vision is also called panoramic. That is, each eye gives a 180-degree view. This pest is almost impossible to take 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.

Is there some more interesting feature visual perception by a fly of a palette of colors. After all, almost all species differently perceive certain colors that are familiar to our eyes. Some of them insects do not distinguish at all, others look different to them, in other colors.

By the way, in addition to two compound eyes, the fly has three more simple eyes. They are located in the interval between the faceted ones, on the frontal part of the head. Unlike compound eyes, these three are used by insects to recognize one or another object in close proximity.

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

World view

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

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

And yet these pests tend to perceive well only smaller and moving objects. The insect does not distinguish between such large items like a person, for example. For a fly, this is nothing more than another part of the interior of the environment.

But the approach of a hand to an insect is perfectly captured by its eyes and promptly gives the necessary signal to the brain. Just like any other rapidly approaching danger, it will not be difficult for these rogues, thanks to the sophisticated 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, like all insects, have an amazing visual apparatus, allowing them not to lose vigilance, and in the daytime to keep all-round observational defense one hundred percent.

The sight of the 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.

Insects perceive light in three ways: the entire surface of the body, simple eyes and complex, so-called compound eyes.

As experiments have shown, caterpillars, larvae of water beetles, aphids, beetles (even blind cave beetles), flour worms, cockroaches and, of course, many other insects feel the light on the entire surface of the body. Light penetrates through the cuticle to the head and causes appropriate reactions in the brain cells that perceive it.

The most primitive simple eyes, perhaps, are found in the larvae of some mosquitoes. These are age spots with a small number of photosensitive cells (there are often only two or three of them). In larvae of sawflies (order Hymenoptera) and beetles, the eyes are more complex: fifty or more photosensitive cells covered from above with a transparent lens - a thickening of the cuticle.

Red eyes of a caterpillar. Photo: Jess

On each side of the head of the larvae of the horse beetle there are six eyes, two of which are much larger than the others (they contain 6 thousand visual cells). Do they see well? They are hardly capable of conveying to the brain an impression of the shape of an object. However, the approximate dimensions of what they saw, two large eyes detect well.

The larva sits in a vertical burrow dug in the sand. From a distance of 3-6 centimeters, she notices a victim or an enemy. If an insect crawling close is no more than 3-4 millimeters, the larva grabs it with its jaws. When more, hides in a mink.
Five or six simple eyes on each side of the head of the caterpillars each contain only one "ritinal stick" - a visual element - and are covered from above with a lens capable of concentrating light.

Each eye separately does not give an idea of the shape of the observed object. However, in experiments, the caterpillar showed amazing abilities. She sees vertical objects better than horizontal ones. Of the two pillars or trees, he chooses the higher one and crawls towards it, even if all her simplest eyes are sealed with black paint, leaving only one. In every this moment he sees only a point of light, but the caterpillar turns its head, examining different points of the object in turn with its only eye, and this is enough for an approximate picture of what it saw to form in its brain. Of course, the caterpillar notices the obscure, indistinct, but nevertheless the object shown to it.

Simple eyes are typical of insect larvae; however, many adults also have them. In the latter, the main thing is the so-called complex, or faceted, eyes: on the sides of the head. They are composed of many elongated simple eyes - ommatidia. Each ommatidia contains a light-perceiving cell connected by a nerve to the brain. Above it is an elongated lens. Both, the photosensitive cell and the lens, are surrounded by a light-impervious sheath of pigment cells. Only a hole is left at the top, but there the lens is covered by a transparent cuticular cornea. It is common to all ommatidia, closely adjacent to each other and connected into one compound eye. It can only have 300 ommatidia (female firefly), 4000 ( housefly), 9,000 (floating beetle), 17,000 (butterflies) and 10,000-28,000 in various dragonflies.

The compound eyes of the Monarch butterfly. Photo: Monica R.

Each ommatidium transmits to the brain only one point from the entire complex picture of the world surrounding the insect. From the many individual points seen by each of the ommatidia, a mosaic "panel" of landscape objects is formed in the insect's brain.
In nocturnal insects (fireflies, other beetles, moths), this mosaic picture of optical vision is, so to speak, more blurred. At night, the pigment cells separating the ommatidia of the compound eye from each other, shrinking, are pulled upwards, to the cornea. Rays of light entering each facet are perceived not only by its light-sensitive cell, but also by cells located in neighboring ommatidia. After all, now they are not covered with dark pigment “curtains”. This achieves a more complete capture of light, which is not so much in the darkness of the night.

During the day, pigment cells fill all the gaps between the ommatidia, and each of them perceives only those rays that its own lens concentrates. In other words, the "superpositional" eye of nocturnal insects, as it is called, functions during the day as the "appositional" eye of diurnal insects.

No less important than the number of facets, their other feature is the angle of view of each ommatidium. The smaller it is, the higher the resolution of the eye and the finer details of the observed object it can see. An earwig ommatidium has an angle of view of 8 degrees, a bee has a 1 degree angle of view. It is calculated that for every point in the mosaic picture of what the bee saw with the earwig, there are 64 points. Consequently, the small details of the observed object are captured by the bee's eye ten times better.
But less light enters the eye with a smaller angle of view. Therefore, the size of the facets in the complex eyes of insects is not the same. Larger facets are located in those directions where a brighter visibility is needed and an accurate examination of details is not so necessary. In a horsefly, for example, the facets in the upper half of the eye are noticeably larger than those in the lower.
Some flies also have similar clearly divided arenas with different-sized ommatidia. The bee has a different arrangement of facets: their angle of view in the direction of the horizontal axis of the body is two to three times greater than along the vertical.

Twirl beetles and male mayflies essentially have two eyes on each side: one with large, the other with small facets.
Remember how a caterpillar, examining an object with just one eye (the others were smeared with paint), could, however, form a well-known, though very rough, idea of its shape. She, turning her head, looked at the whole object in parts, and the memory apparatus of the brain added all the points seen at each given moment into a single impression. Insects with compound eyes do the same: when looking at something, they turn their heads. A similar effect is achieved without turning the head when the observed object is moving or when the insect itself is flying. Compound eyes see better in flight than at rest.
A bee, for example, is able to constantly keep in view an object that flickers 300 times per second. And our eye will not notice even six times slower flashing.

Insects see close objects better than far ones. They are very nearsighted. The clarity of what they see is much worse than ours.
An interesting question: what colors do insects distinguish? Experiments have shown that bees and carrion flies see the shortest wavelengths of the spectrum (297 millimicrons) that are only found in sunlight. Ultraviolet - our eye is completely blind to it - is also distinguished by ants, moths and, obviously, many other insects.

Insect eyes. Photo: USGS Bee Inventory and Monitoring Laboratory

Insects have different sensitivity to the opposite end of the spectrum. The bee is blind to red light: it is the same as black for it. The longest waves it still perceives are 650 millimicrons (somewhere on the border between red and orange). Wasps, trained to come for food on black tables, confuse them with red ones. Red is not seen by some butterflies, for example, satyrs. But others (urticaria, cabbage) distinguish red. The record, however, belongs to the firefly: it sees dark red with a wavelength of 690 millimicrons. None of the studied insects was capable of this.
For human eye The brightest part of the spectrum is yellow. Experiments with insects have shown that in some the green part of the spectrum is perceived by the eye as the brightest, in the bee it is ultraviolet, in the drop fly the highest brightness was observed in the red, blue-green and ultraviolet bands of the spectrum.

Undoubtedly butterflies, bumblebees, some flies, bees and other insects that visit flowers distinguish colors. But to what extent and which ones, we still know little. More research is needed.
The most numerous experiments have been carried out with bees in this respect. The bee sees the surrounding world, painted in four primary colors: red-yellow-green (not each of those named separately, but together, together, like a single color unknown to us), then blue-green, blue-violet and ultraviolet. Then how to explain that bees also fly to red flowers, to poppies, for example? They, and many whites and yellow flowers reflect a lot ultraviolet rays so the bee sees them. What color they are painted for her eyes, we do not know.

Butterflies apparently have color vision closer to ours than bees. We already know that some butterflies (urticaria and cabbage) distinguish red. They see ultraviolet, but it does not play such a big role for them as in the visual perceptions of bees. These butterflies are most attracted to two colors - blue-violet and yellow-red.
It has been proven by various methods that many other insects also distinguish colors, and in the best way the colors of plants on which they feed or breed. Some hawks, leaf beetles, aphids, swedish flies, land bugs and smooth water bugs are far from complete list such insects. It is interesting that the smoothness has only the upper and rear end eyes has color vision, bottom and front - no. Why so, it is not clear.

In addition to the perception of ultraviolet rays, another property of the insect eye that our eyes lack is sensitivity to polarized light and the ability to navigate by it. Not only compound eyes, but also simple eyes, as shown by experiments with caterpillars and hymenoptera larvae, are able to perceive polarized light. We looked at the eyes of some under an electron microscope, and found in the retinal light-sensitive rod molecular structures that apparently act like a polaroid.

Some Observations recent years convince: nocturnal insects have organs that capture infrared rays.

Flies live less than elephants. There is no doubt about this. But, from the point of view of flies, does their life really seem much shorter to them? That, in fact, was the question posed by Kevin Geely of Trinity College Dublin in an article just published in Animal Behavior. His answer: obviously not. These small fly creatures with fast metabolisms see the world in slow motion. The subjective experience of time is essentially only subjective. Even individual people who can exchange impressions by talking to each other, cannot know for sure whether their own experience with other people's experience.

Flies - the vision of a fly and why it is difficult to kill it

But an objective indicator, which probably correlates with subjective experience, does exist. It is called the critical flicker-fusion frequency CFF, and is the lowest frequency at which flickering light is produced by a constant light source. It measures how quickly an animal's eyes can update images and thus process information.

For humans, the average critical flicker frequency is 60 hertz (that is, 60 times per second). That is why the refresh rate of the image on the television screen is usually set to this value. Dogs have a critical flicker frequency of 80Hz, which is probably why they seem to dislike watching TV. For a dog, a TV program looks like a lot of photo frames that quickly change each other.

A higher critical flicker frequency should mean biological benefits, as it allows faster response to threats and opportunities. Flies with a critical flicker frequency of 250 Hz are notoriously difficult to kill. A folded newspaper, which appears to a person to move rapidly during a strike, appears to flies as if it were moving in molasses.

Scientist Kevin Geely suggested that the main factors that limit the critical frequency of flicker in an animal are its size and metabolic rate. small size means that signals travel a shorter distance to the brain. High speed metabolism means more energy is available to process them. A search in the literature, however, showed that no one had previously been interested in this issue.

Fortunately for Gili, this very search also revealed that many people had studied the critical flicker frequency of a large number species for other reasons. Many scientists have also studied metabolic rates in many of the same species. But data on the size of the species are well known. Thus, all he had to do was to build correlations and apply the results of other studies to his advantage. Which he did.

To facilitate the task for his study, the scientist took data relating only to vertebrate animals - 34 species. At the lower end of the scale was the European eel, with a critical flicker frequency of 14 Hz. It is immediately followed by a leatherback turtle, with a critical flicker frequency of 15 Hz. Reptiles of the tuatara species (tuatara) have a CFF of 46 Hz. Hammerhead sharks, along with humans, have a CFF of 60 Hz, and yellowtip birds, like dogs, have a CFF of 80 Hz.

The first place was taken by the golden gopher, with a CFF of 120 Hz. And when Gili plotted the CFF against animal size and metabolic rate (which are not, admittedly, independent variables, since small animals tend to have higher metabolic rates than large ones), he found exactly the correlations which he predicted.

It turns out that his hypothesis - that evolution makes animals see the world in as slow motion as possible - looks correct. The life of a fly may seem short to humans, but from the point of view of the Diptera themselves, they can live to a ripe old age. Keep this in mind the next time you try (unsuccessfully) to kill another fly.