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Animal soil. Soil animals Animals living in the upper layer of the earth

how animal habitat soil very different from water and air. The soil is a loose thin surface layer of land in contact with the air. Despite its small thickness, this shell of the Earth plays a crucial role in the spread of life. The soil is not just a solid body, like most rocks of the lithosphere, but a complex three-phase system in which solid particles are surrounded by air and water. It is penetrated by cavities filled with a mixture of gases and aqueous solutions, and therefore extremely diverse conditions are created in it, favorable for the life of many micro- and macroorganisms. In the soil, temperature fluctuations are smoothed in comparison with the surface air layer, and the presence of groundwater and the penetration of precipitation create moisture reserves and provide a moisture regime that is intermediate between the aqueous and terrestrial environments. The soil concentrates the reserves of organic and mineral substances supplied by dying vegetation and animal carcasses. All this determines high soil saturation with life.

To every animal to live need to breathe. Conditions for breathing in soil are different than in water or in air. Soil contains particulate matter, water and air. Particles in the form of small lumps occupy a little more than half the volume of soil; the remaining volume falls into the share of gaps - pores that can be filled with air (in dry soil) or water (in soil saturated with moisture).

Moisture in the soil present in various conditions:

bound (hygroscopic and film) is firmly held by the surface of soil particles;
capillary occupies small pores and can move along them in various directions;
gravitational fills larger voids and slowly seeps down under the influence of gravity;
vapor is found in soil air.

Composition soil air changeable. With depth, the oxygen content in it drops sharply and the concentration of carbon dioxide increases. Due to the presence of decomposing organic substances in the soil, there may be a high concentration of toxic gases such as ammonia, hydrogen sulfide, methane, etc. When the soil is flooded or intensive plant rot remains rotting, completely anaerobic conditions may occur in places.

Temperature fluctuations cutting only on the surface of the soil. Here they can be even stronger than in the surface layer of air. However, with each centimeter in depth, daily and seasonal temperature changes are becoming smaller and practically no longer visible at a depth of 1-1.5 m.

All these features lead to the fact that, despite the large heterogeneity of environmental conditions in the soil, it acts as fairly stable environment, especially for motile organisms. It is clear that animals can move relatively quickly in the soil only in natural voids, cracks, or previously dug passages. If none of this is in the way, then the animal can advance only by breaking the course and scooping up the ground back or swallowing the ground and passing it through the intestines.

Inhabitants of the soil. The heterogeneity of the soil leads to the fact that for organisms of different sizes, it acts as a different environment. For microorganisms, the huge total surface of soil particles is of particular importance, since the vast majority of the microbial population is adsorbed on them. Due to this soil structure, numerous animals that breathe through the skin. Moreover, in the soil live hundreds of species of real freshwater animalsinhabiting rivers, ponds and swamps. True, these are all microscopic creatures - lower worms and single-celled protozoa. They move, float in a film of water covering the soil particles. If the soil dries up, these animals secrete a protective shell and, as it were, fall asleep, fall into a state of suspended animation.

Among soil animals there are also predators and those that feed on parts of living plantsmainly rooted. There are in the soil, and consumers of decaying plant and animal residues; it is possible that bacteria play a significant role in their nutrition. "Peaceful" moles eat a huge amount of earthworms, snails and insect larvae, they even attack frogs, lizards and mice. Predators are found among almost all groups of invertebrates living in the soil. Large ciliates feed not only on bacteria, but also on simple animals, such as flagella. Predators include spiders and hayfields close to them.

Soil animals find their food either in the soil itself or on its surface. The vital activity of many of them is very useful. Earthworms are especially useful. They drag a huge amount of plant debris into their burrows, which contributes to the formation of humus and returns to the soil substances extracted from it by the roots of plants.

Not only earthworms “work” in the soil, but also their closest relatives:

whitish annelids (enchitreids, or potato worms),
some types of microscopic roundworms (nematodes),
small ticks
various insects
wood lice,
millipedes
snails.

The purely mechanical work of many animals living in it also affects the soil. They make moves, mix and loosen the soil, dig holes. These are moles, marmots, ground squirrels, jerboas, field and forest mice, hamsters, field voles, mole rats. The relatively large passages of some of these animals go 1–4 m deep. In some places, for example, in the steppe zone, a large number of passages are dug by dung beetles, bears, crickets, tarantulas, ants, and termites in the tropics.

In addition to the permanent inhabitants of the soil, among large animals we can distinguish a large ecological group of inhabitants of burrows (ground squirrels, woodchucks, jerboas, rabbits, badgers, etc.). They feed on the surface, but breed, hibernate, rest, and escape from danger in the soil. A number of other animals use their holes, finding in them a favorable microclimate and shelter from enemies. Norniki possess structural features characteristic of terrestrial animals, but have a number of devices associated with a burrowing lifestyle. For example, badgers have long claws and strong muscles on the forelimbs, a narrow head, and small ears. In rabbits, in comparison with hares that do not dig holes, the ears and hind legs are noticeably shortened, the skull is stronger, the bones and muscles of the forearms are more developed, etc.

The inhabitants of the soil in the process of evolution developed adaptations to appropriate living conditions:

features of the shape and structure of the body,
physiological processes
reproduction and development,
ability to endure adverse conditions, behavior.

The earthworms, nematodes, most millipedes, the larvae of many beetles and flies have a very elongated flexible body, which makes it easy to move in winding narrow passages and cracked soils. The bristles of earthworms and other annelids, hairs and claws of arthropods allow them to significantly accelerate their movements in the soil and hold firmly in burrows, clinging to the walls of passages. How slowly the worm crawls along the surface of the earth and at what speed, in essence, instantly, it hides in its hole. When laying new passages, some soil animals, such as worms, alternately stretch and contract the body. Moreover, abdominal fluid is periodically pumped into the front end of the animal. It swells violently and pushes soil particles. Other animals, such as moles, clear their way by digging the ground with their front paws, which have turned into special digging organs.

The color of animals constantly living in the soil is usually pale - grayish, yellowish, whitish. Their eyes, as a rule, are poorly developed or completely absent. But the organs of smell and touch have developed very subtly.

When we enter the forest on a summer day, we immediately notice fluttering butterflies, singing birds, jumping frogs, rejoice at a running hedgehog, a meeting with a hare. One gets the impression that it is these clearly visible animals that form the basis of our fauna. In fact, animals that are easy to see in the forest are just an insignificant part of it.

The basis of the population of our forests, meadows, fields is composed of soil animals. At first glance, the soil is so lifeless and unsightly, when closely examined, it is literally crammed with life. If you look closely, unusual paintings will open.

It’s easy to see some inhabitants of the soil. These are earthworms, millipedes, insect larvae, small mites, wingless insects. Others can be examined with a microscope. In the thinnest films of water that envelop the soil particles, rotifers scurry around, flagellates, amoeba crawl, roundworms wriggle. How many real workers are here, indistinguishable to the naked eye, but still doing a titanic job! All these inconspicuous creatures keep our common home - Earth, clean. Moreover, they still warn of the danger that threatens this house when people are unreasonably behaving towards nature.

In the soil of central Russia on 1 m 2 you can find up to 1 thousand species of soil inhabitants that vary greatly in number: up to 1 million ticks and springtails, hundreds of millipedes, insect larvae, earthworms, about 50 million roundworms, but the number of protozoa is even difficult estimate.

This whole world, living according to its own laws, provides for the processing of dead plant debris, the cleaning of soil from them, and the maintenance of a water-resistant structure. Soil animals constantly plow the soil, moving upward particles from the lower layers.

In all terrestrial ecosystems, the vast majority of invertebrates (both in the number of species and in the number of individuals) are inhabitants of the soil or are closely related to the soil at a certain period of their life cycle. According to Boucle's calculations (1923), the number of insect species associated with soil is 95–98%.

By the ability to adapt to living conditions, there are no equal nematodes among animals. In this regard, they can only be compared with bacteria and simple unicellular organisms. Such universal adaptability is largely due to the development of a dense outer cuticle in nematodes, which increases their vitality. In addition, the shape of the body and the nature of the movements of the nematodes proved to be suitable for life in various environments.

Nematodes take part in the mechanical destruction of plant tissues: they “drill” into dead tissue and, with the help of secreted enzymes, destroy cell walls, opening the way for bacteria and fungi to penetrate.

In our country, crop losses of vegetables, grains and industrial crops due to damage by roundworms sometimes reach 70%.

The formation of tumors - galls - on the roots of the host plant causes another pest - southern gall nematode(Meloidogyne incognita) It causes the greatest harm to vegetable growing in the southern regions, where it is found in open ground. In the north, it is found only in greenhouses, mainly damaging cucumbers and tomatoes. The main harm is done by females, while males, having completed development, go out into the soil and do not feed.

Soil nematodes are notorious: they see primarily pests of cultivated plants. Nematodes destroy the roots of potatoes, onions, rice, cotton, sugarcane, sugar beets, ornamental and other plants. Zoologists are developing measures to combat them in the fields and in greenhouses. A great contribution to the study of this group of animals was made by the famous evolutionary biologist A.A. Paramonov.

Nematodes have long attracted the attention of evolutionists. They are not only extremely diverse, but also amazingly resistant to physical and chemical factors. Wherever these worms begin to be studied, new species unknown to science are everywhere found. In this regard, nematodes seriously claim the second - after insects - place in the animal world: experts believe that there are at least 500 thousand species, but there is reason to believe that the true number of nematodes is much higher.

General characteristics.

Soil - is a product of the vital activity of organisms, including microorganisms, both modern and belonging to the "former biospheres." Soil is the most important component of any ecological system of land, on the basis of which the development of plant communities takes place, which in turn form the basis of the food chains of all other organisms that form the ecological systems of the Earth, its biosphere. People are not an exception here: the well-being of any human society is determined by the availability and condition of land resources, soil fertility.

Meanwhile, over the historical time on our planet, up to 20 million km2 of agricultural land has been lost. For every inhabitant of the Earth today, on average, only 0.35-0.37 hectares, while in the 70s this value was 0.45-0.50 hectares. If the current situation does not change, then in a century, at such a rate of loss, the total area of \u200b\u200bland suitable for agriculture will be reduced from 3.2 to 1 billion hectares.

V.V. Dokuchaev identified 5 main parent factors:

· Climate;

· Mother rock (geological basis);

· Topography (relief);

· alive organisms;

Currently, another factor in soil formation can be called human activities.

Soil formation begins with primary succession, which is manifested in physical and chemical weathering, leading to loosening from the surface of parent rocks, such as basalts, gneisses, granites, limestones, sandstones, and shales. This weathering layer is gradually colonized by microorganisms and lichens, which transform the substrate and enrich it with organic substances. As a result of lichen activity, primary plant nutrients, such as phosphorus, calcium, potassium, and others, accumulate in primary soil. On this primary soil, plants can now settle and form plant communities that define the face of biogeocenosis.

Gradually, deeper layers of the earth are involved in the process of soil formation. Therefore, most soils have a more or less pronounced layered profile, divided into soil horizons. A complex of soil organisms settles in the soil - edafon : bacteria, fungi, insects, worms and burrowing animals. Edafon and plants are involved in the formation of soil detritus, which detritophages - worms and insect larvae - pass through their bodies.

For example, earthworms on a hectare of land process about 50 tons of soil per year.

During the decomposition of plant detritus, humic substances are formed - weak organic humic and fulvic acids - the basis of soil humus. Its content ensures the structure of the soil and the availability of mineral nutrients to plants. The thickness of the humus-rich layer determines soil fertility.

The composition of the soil includes 4 important structural components:

· Mineral base (50-60% of the total soil composition);

· Organic matter (up to 10%);

· Air (15-20%);

Water (25-35%).

Mineral base - an inorganic component formed from the parent rock as a result of its weathering. Mineral fragments vary in size (from boulders to grains of sand and tiny particles of clay). This is the skeletal material of the soil. It is divided into colloidal particles (less than 1 μm), fine soil (less than 2 mm) and large fragments. The mechanical and chemical properties of the soil are determined by fine particles.

The soil structure is determined by the relative content of sand and clay. The soil that contains sand and clay in equal amounts is most favorable for plant growth.

In soil, as a rule, 3 main horizons are distinguished, differing in mechanical and chemical properties:

· Upper humus-accumulative horizon (A) in which organic matter is accumulated and converted, and from which part of the compounds is washed down by washing water.

· Washout horizon or illuvial (B) where substances washed from above settle and transform.

· Maternal breed or horizon (C), material that is converted to soil.

Within each layer, more fractional horizons are distinguished that differ in their properties.

The main properties of the soil as an environmental medium are its physical structure, mechanical and chemical composition, acidity, redox conditions, organic matter content, aeration, moisture capacity and moisture content. Various combinations of these properties form many varieties of soils. In terms of prevalence on Earth, five typological groups of soils occupy a leading position:

soils of moist tropics and subtropics, mainly red earth and yellow earth characterized by rich mineral composition and high mobility of organics;
fertile soils of savannah and steppes - chernozems, chestnut and brown soils with a powerful humus layer;
scarce and extremely unstable soils of deserts and semi-deserts belonging to different climatic zones;
relatively poor soils of temperate forests - podzolic, sod-podzolic, brown and gray forest soils ;
permafrost soils, usually thin, podzolic, wading , glue depleted in mineral salts with a poorly developed humus layer.

Floodplain soils are found along river banks;

A separate group are saline soils: salt flats, salt licks, and etc. which account for 25% of the soils.

Salt marshes - the soil is constantly heavily moistened with salt water up to the surface, for example, around bitter-salty lakes. In summer, the surface of the salt marshes dries, becoming covered with a crust of salt.

Solonetz - the surface is not saline, the top layer is leached, structureless. The lower horizons are densified, saturated with sodium ions, when dried, crack on poles, blocks. The water regime is unstable - in the spring - stagnation of moisture, in the summer - severe drying out.

Salt marshes

Solanchaky salt licks

Saline soil (slightly salted)

Organic matter of the soil.

Each type of soil corresponds to a certain plant, animal world and a combination of bacteria - edafon. Dying or dead organisms accumulate on the surface and inside the soil, forming the organic matter of the soil, called humus . The process of humification begins with the destruction and grinding of organic matter by vertebrates, and then is converted by fungi and bacteria. These animals include phytophages eating tissues of living plants, saprophages consuming dead plant matter necrophages eating corpses of animals coprophages destroying animal excrement. All of them make up a complex system, called saprophilic animal complex .

Humus differs in type, form and nature of its constituent elements, which are divided into humic and non-humic substances. Non-humic substances are formed from compounds included in the tissues of plants and animals, for example, proteins and carbohydrates. When these substances are decomposed, carbon dioxide, water, and ammonia are released. The energy generated by this is used by soil organisms. In this case, the complete mineralization of the batteries occurs. Humic substances as a result of the vital activity of microorganisms are processed into new, usually high molecular weight compounds - humic acids or fulvic acids .

Humus is divided into nutritious, which is easily processed and serves as a source of nutrition for microorganisms and sustainable, which performs physical and chemical functions, controlling the balance of the nutrient, the amount of water and air in the soil. Humus tightly sticks together mineral particles of the soil, improving its structure. Soil structure also depends on the amount of calcium compounds. The following soil structures are distinguished:

· mealy

· powdery

· grainy

· nutty

· lumpy

· clay.

The dark color of humus contributes to better heating of the soil, and its high moisture capacity - to water retention by the soil.

The main property of the soil is its fertility, i.e. ability to provide plants with water, mineral salts, air. The thickness of the humus layer determines the fertility of the soil.

Humidity and aeration.

Soil water is divided into:

· gravitational

· hygroscopic

· capillary

· vaporous

Gravity water is mobile, it is the main type of mobile water, fills wide gaps between soil particles, seeps down under the action of gravity until it reaches groundwater. Plants easily absorb it.

Hygroscopic water in the soil is retained by hydrogen bonds around individual colloidal particles in the form of a thin, strong bound film. It is released only at a temperature of 105 - 110 ° C and is practically inaccessible to plants. The amount of hygroscopic water depends on the content of colloidal particles in the soil. In clay soils it is up to 15%, in sandy soils - 5%.

As the amount of hygroscopic water accumulates, it passes into capillary water, which is held in the soil by surface tension forces. Capillary water easily rises to the surface in pores from groundwater, easily evaporates, and is freely absorbed by plants.

Vaporous moisture occupies all water-free pores.

There is a constant exchange of soil, groundwater and surface water, changing its intensity and direction depending on the climate and seasons.

All moisture-free pores are filled with air. On light (sandy) soils, aeration is better than on heavy (clay) soils. Air and humidity conditions are related to precipitation.

Ecological groups of soil organisms.

On average, the soil contains 2-3 kg / m2 of live plants and animals, or 20-30 t / ha. Moreover, in the temperate zone, plant roots are 15 t / ha, insects 1 t, earthworms - 500 kg, nematodes - 50 kg, crustaceans - 40 kg, snails, slugs - 20 kg, snakes, rodents - 20 g, bacteria - 3 t, mushrooms - 3 t, actinomycetes - 1.5 tons, protozoa - 100 kg, algae - 100 kg.

The heterogeneity of the soil leads to the fact that for different organisms it acts as a different environment. According to the degree of connection with soil as a habitat animalscombine in 3 groups:

· Geobionts - animals constantly living in the soil (earthworms, primary wingless insects).

· Geophylls - animals, part of the cycle of which necessarily passes in the soil (most insects: locusts, a number of beetles, long-legged mosquitoes).

· Geoxenes - animals that sometimes visit the soil for temporary shelter or shelter (cockroach, many semi-rigid, hard-winged, rodents, and other mammals).

Depending on the size of soil inhabitants, it can be divided into the following groups.

· Microbiotype, microbiota - soil microorganisms, the main link of the detrital chain, an intermediate link between plant residues and soil animals. These are green, blue-green algae, bacteria, fungi, protozoa. The soil for them is a system of microcurrents. They live in soil pores. Able to tolerate freezing soil.

· Macrobiotype, Macrobiota - large soil animals, up to 20 mm in size (insect larvae, millipedes, earthworms, etc.). the soil for them is a dense medium that exerts strong mechanical resistance during movement. They move in the soil expanding natural wells by moving soil particles or digging new passages. In this regard, they developed adaptations for digging. Often there are specialized respiratory organs. They also breathe through the integument of the body. In winter and in the arid period, they move into deep soil layers.

· Megabyte, megabyte - large excavations, mainly from mammals. Many of them spend their lives in the soil (gold moles, mole rats, zokors, moles of Eurasia, marsupial moles of Australia, mole rats, etc.). Lay a system of holes and moves in the soil. Their eyes are underdeveloped, a compact, swollen body with a short neck, short thick fur, strong compact limbs, digging limbs, strong claws.

· The inhabitants of the holes - badgers, marmots, ground squirrels, jerboas, etc. They feed on the surface, breed, winter, rest, sleep, and escape from danger in soil burrows. The structure is characteristic of terrestrial ones, however, they have adaptations of norns — strong claws, strong muscles on the forelimbs, a narrow head, and small auricles.

· Psammophiles - residents of loose sand. They have peculiar limbs, often in the form of “skis”, covered with long hairs, horny outgrowths (thin-toed gopher, crested jerboa).

· Gallophiles - residents of saline soils. They have devices for protection against excess salts: dense covers, devices for removing salts from the body (larvae of desert black beetles).

Plants are divided into groups depending on the demands on soil fertility.

· Eutotrophic or eutrophic - grow on fertile soils.

· Mesotrophic - less demanding on soil fertility.

· Oligotrophic - content with a small amount of nutrients.

The following groups are distinguished depending on the demands of plants for individual soil microelements.

· Nitrophils - are demanding on the presence of nitrogen in the soil, settle where there are additional sources of nitrogen - felling plants (raspberries, hops, bindweed), garbage (nettle shiritsa, umbrella), pasture plants.

· Calciophiles - demanding on the presence of calcium in the soil, settle on carbonate soils (venus slipper, Siberian larch, beech, ash).

· Calciophobia - plants avoiding soils with a high calcium content (sphagnum mosses, marsh, heather, warty birch, chestnut).

Depending on the pH requirements of the soil, all plants are divided into 3 groups.

· Acidophils - plants that prefer acidic soils (heather, whitebird, sorrel, small sorrel).

· Basifillas - plants that prefer alkaline soils (coltsfoot, field mustard).

· Neutrophils - plants that prefer neutral soils (meadow foxtail, meadow fescue).

Plants growing on saline soils are called halophytes (European soleros, sarsazan cone), and plants that cannot withstand excessive salinization - glycophytes . Halophytes have high osmotic pressure, which allows the use of soil solutions, are capable of secreting excess salts through the leaves or accumulating them in your body.

Plants adapted to loose sand are called psammophytes . They are able to form subordinate roots when they are covered with sand, subordinate buds form on the roots when they are exposed, often have high shoot growth rates, flying seeds, strong covers, have air chambers, parachutes, propellers - devices for not filling with sand. Sometimes a whole plant is able to break away from the ground, dry and, together with the seeds, be transported by wind to another place. Shoots sprout quickly, arguing with the dune. There are adaptations for the transfer of drought - covers on the roots, root sampling, strong development of lateral roots, leafless shoots, xeromorphic foliage.

Plants growing in peat bogs are called oxylophytes . They are adapted to high soil acidity, strong moisture, anaerobic conditions (ledum, sundew, cranberries).

Plants that live on stones, rocks, talus rocks belong to lithophytes. As a rule, these are the first settlers on rocky surfaces: autotrophic algae, scale lichens, leaf lichens, mosses, lithophytes from higher plants. They are called crevice plants - hasmophytes . For example, saxifrage, juniper, pine.

T.V. Lukarevskaya

In the soil of central Russia per 1 m2, you can see up to 1 thousand species of soil inhabitants that vary greatly in number: up to 1 million ticks and springtails, hundreds of millipedes, insect larvae, earthworms, about 50 million roundworms, but the number of protozoa is difficult to estimate .

Centipede

Earthworm

Nematodes take part in the mechanical destruction of plant tissues: they "drill" into dead tissue and, with the help of secreted enzymes, destroy cell walls, opening the way for bacteria and fungi to penetrate.

In our country, crop losses of vegetables, grains and industrial crops due to damage by roundworms sometimes reach 70%.

Nematode

The formation of tumors - galls - on the roots of the host plant causes another pest - the southern gall nematode (Meloidogyne incognita). It causes the greatest harm to vegetable growing in the southern regions, where it is found in open ground. In the north, it is found only in greenhouses, mainly damaging cucumbers and tomatoes. The main harm is done by females, while males, having completed development, go out into the soil and do not feed.

Around us: on earth, in grass, on trees, in the air - life boils everywhere. Even a resident of a big city, never having ever delved into the forest, often sees birds, dragonflies, butterflies, flies, spiders and many other animals around him. Well known to all and the inhabitants of the reservoirs. Everyone, at least occasionally, had to see schools of fish near the shore, water beetles or snails.

But there is a world hidden from us, inaccessible to direct observation - a peculiar world of animal soil.

There is eternal darkness, you cannot penetrate there without destroying the natural structure of the soil. And only some randomly noticed signs show that under the surface of the soil, among the roots of plants, there is a rich and diverse world of animals. This is sometimes indicated by mounds above mole minks, ground squirrel holes in the steppe or shore swallow holes in a cliff above the river, heaps of land on paths thrown out by earthworms, and they themselves, crawling out after the rain, unexpectedly literally from the ground, masses of winged ants or the fat larvae of May beetles that come across when digging the ground.

Soil is usually called the surface layer of the earth's crust on land, formed during the weathering of the parent rock under the influence of water, wind, temperature fluctuations and the activity of plants, animals and humans. The most important property of soil that distinguishes it from a barren mother breed is fertility, that is, the ability to produce plants (see art. "").

As an animal habitat, the soil is very different from water and air. Try to wave your hand in the air - you will not notice almost no resistance. Do the same in water - you will feel significant resistance to the environment. And if you lower your hand into the pit and fill it with earth, even pulling it out will be difficult, not like moving it from side to side. It is clear that animals can move relatively quickly in the soil only in natural voids, cracks, or previously dug passages. If none of this exists, then the animal can advance only by breaking through the course and scooping up the earth back, or by “eating through” the course, that is, by swallowing the ground and passing it through the intestines. The speed of movement will, of course, be negligible.

Digging animals and their moves in the soil: 1 - toad; 2 - cricket; 3 - field mouse; 4 bears; 5 - shrew; 6 - mole.

Every animal needs to breathe in order to live. Conditions for breathing in soil are different than in water or in air. Soil contains particulate matter, water and air. Solid particles in the form of small lumps occupy a little more than half of its volume; the rest falls on the gaps — pores that can be filled with air (in dry soil) or water (in soil saturated with moisture). As a rule, water covers all soil particles with a thin film; the rest of the space between them is occupied by air saturated with water vapor.

Due to this soil structure, numerous animals breathing through the skin can live in it. If they are removed from the ground, they quickly die from drying out. Moreover, hundreds of species of real freshwater animals live in the soil - the very ones that inhabit rivers, ponds and swamps. True, these are all microscopic creatures - lower worms and single-celled protozoa. They move, float in a film of water covering the soil particles.

If the soil dries, they release a protective shell and cease to be active for a long time.

Soil air receives oxygen from the atmosphere: its amount in soil is 1-2% less than in atmospheric air. Oxygen is consumed in the soil by animals, microorganisms, and plant roots. All of them emit carbon dioxide. In the soil air it is 10-15 times more than in the atmosphere. Free gas exchange between soil and atmospheric air can occur only if the holes between the solid particles are not completely filled with water. After heavy rains or in spring, after snow melts, the soil is saturated with water. There is not enough air in the soil, and many animals tend to leave the soil under the threat of death. This explains the appearance of earthworms on the surface after heavy rains.

Among the soil animals there are predators, and eating parts of living plants, mainly roots. There are also consumers of decomposing plant and animal residues in the soil - it is possible that bacteria play a significant role in their nutrition.

Soil animals find their food either in the soil itself or on its surface. The vital activity of many of them is very useful. The activity of earthworms, which drag a huge amount of plant debris into their burrows, is especially useful: this contributes to the formation of humus and returns to the soil substances extracted from it by the roots of plants.

In forest soils, invertebrates, especially earthworms, process more than half of all fallen leaves. For a year on each hectare they throw to the surface up to 25-30 T of the land they cultivated, turned into good, structural soil. If you distribute this land evenly over the entire surface of a hectare, you get a layer of 0.5-0.8 cm. Therefore, earthworms are not in vain considered the most important soil formers.

Not only earthworms “work” in the soil, but also their closest relatives - smaller whitish annelids (enchitreids, or potato worms), as well as some types of microscopic roundworms (nematodes), small mites, various insects, especially their larvae, and finally, wood lice, millipedes, and even snails.

The purely mechanical work of many animals living in it also affects the soil. They make moves in the soil, mix and loosen it, dig holes. All this increases the number of voids in the soil and facilitates the penetration of air and water into its depths.

Such “work” involves not only relatively small invertebrate animals, but also many mammals - moles, shrews, woodchucks, ground squirrels, jerboas, field and forest mice, hamsters, voles, mole rats. The relatively large passages of some of these animals penetrate the soil to a depth of 1 to 4 m.

The passages of large earthworms go even deeper: in most worms they reach 1.5–2 m, and in one southern worm even up to 8 m. These passages, especially in denser soils, are constantly used by plant roots penetrating deep into them.

In some places, for example, in the steppe zone, a large number of passages and burrows in the soil are dung beetles, bears, crickets, tarantula spiders, ants, and termites in the tropics.

Many soil animals feed on roots, tubers, and plant bulbs. Those that attack cultivated plants or forest stands are considered pests, such as the chafer. Its larva lives in the soil for about four years and pupates there. In the first year of life, it feeds mainly on the roots of herbaceous plants. But, growing up, the larva begins to feed on the roots of trees, especially young pines, and causes great harm to the forest or forest stands.

The larvae of nutcracker beetles, black beetles, weevils, pollen eaters, caterpillars of some butterflies, for example, gnawing scoops, the larvae of many flies, cicadas and, finally, root aphids, such as phylloxera, also feed on the roots of various plants, greatly harming them.

A large number of insects that damage the aerial parts of plants - stems, leaves, flowers, fruits - lay eggs in the soil; here, the larvae that emerged from the eggs hide for a period of drought, winter, pupate.

Soil pests include some types of ticks and millipedes, naked slugs and extremely numerous microscopic roundworms - nematodes. Nematodes penetrate from the soil into the roots of plants and disrupt their normal functioning.

Many predators live in the soil. "Peaceful" moles and shrews eat a huge amount of earthworms, snails and insect larvae, they even attack frogs, lizards and mice. They eat almost continuously. For example, a shrew per day eats the amount of living creature equal to its own weight!

Predators are among almost all groups of invertebrates living in the soil. Large ciliates feed not only on bacteria, but also on simple animals, such as flagellates. The ciliates themselves prey on some roundworms. Predatory mites attack other ticks and tiny insects. Thin, long, pale-colored millipede geophiles living in cracked soils, as well as larger dark-colored drupes and scolopendra, which are kept under stones, in stumps, in forest litter, are also predators. They feed on insects and their larvae, worms and other small animals. Predators include spiders and hayfields close to them (“mow-mow-leg”). Many of them live on the surface of the soil, in the litter or under objects lying on the ground.

Many predatory insects live in the soil: ground beetles and their larvae, which play a significant role in the extermination of insect pests, many ants, especially larger species that destroy a large number of harmful caterpillars, and, finally, the famous ant lions, so named because their larvae hunt for ants. The ant lion larva has strong sharp jaws, its length is about 1 cm.The larva digs in a dry sandy soil, usually on the edge of a pine forest, a funnel-shaped fossa and burrows at its bottom in the sand, exposing only its wide open jaws. Small insects falling on the edge of the funnel, most often ants, roll down. The ant lion's larva grabs them and sucks them.

In some places in the soil there is a predatory ... mushroom! The mycelium of this fungus, bearing a tricky name - the didimozoophage, forms special hunting rings. Small soil worms, nematodes, fall into them. With the help of special enzymes, the fungus dissolves the rather strong shell of the worm, grows inside its body and eats it clean.

In the process of adapting to living conditions in the soil, a number of features were developed among its inhabitants in the form and structure of the body, in physiological processes, reproduction and development, in the ability to endure adverse conditions and in behavior. Although each type of animal has peculiarities unique to it, the organization of various soil animals has common features common to entire groups, since the living conditions in the soil are basically the same for all its inhabitants.

The earthworms, nematodes, most millipedes, the larvae of many beetles and flies have a very elongated flexible body, which allows them to easily move in winding narrow passages and cracked soils. The bristles of earthworms and other annelids, hairs and claws of arthropods allow them to significantly accelerate their movements in the soil and hold firmly in burrows, clinging to the walls of passages. See how slowly the worm crawls along the surface of the earth and at what speed, in essence, instantly, it is hiding in its hole. Paving new moves, many soil animals alternately stretch and contract the body. Moreover, abdominal fluid is periodically pumped into the front end of the animal. Is he. strongly swells and pushes soil particles. Other animals make their way, digging the ground with their front legs, which have turned into special digging organs.

The color of animals constantly living in the soil is usually pale - grayish, yellowish, whitish. Their eyes, as a rule, are poorly developed or completely absent, but their organs of smell and touch are very finely developed.

Scientists believe that life originated in the primeval ocean and only much later spread from here to land (see art. ""). It is quite possible that for some terrestrial animals the soil was a transitional medium from life in water to life on land, since the soil is a habitat, intermediate in its properties between water and air.

There was a time when only aquatic animals existed on our planet. After many millions of years, when land had already appeared, some of them fell ashore more often than others. Here, fleeing from drying out, they buried themselves in the ground and gradually adapted to permanent life in the primary soil. Millions of years have passed. The descendants of some soil animals, who developed devices for protection against drying out, finally got the opportunity to go to the surface of the earth. But they probably could not stay here for the first time for long. And they must have come out only at night. Until now, the soil has provided shelter not only for “its own,” soil animals living in it permanently, but also for many that come into it only temporarily from ponds or from the surface of the earth to lay eggs, pupate, go through a certain stage of development , escape from heat or cold.

The animal world of the soil is very rich. It includes about three hundred species of protozoa, more than a thousand species of round and annelid worms, tens of thousands of species of arthropods, hundreds of mollusks and a number of vertebrate species.

Among them are both useful and harmful. But the majority of soil animals are still listed in the “indifferent” section. Perhaps this is the result of our ignorance. Studying them is the next task of science.

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