Well known to all earthworms constitute a large group of species belonging to different families of oligochaetes.
Our common earthworm, reaching 30 centimeters in length and a centimeter in thickness, belongs to the most fully studied family of Lumbricidae, which includes about 200 species, about a hundred of them are found in Russia.
Types of earthworms
According to the characteristics of the biology of earthworms, earthworms can be divided into two types: the first includes worms that feed on the soil surface, the second - those that feed in the soil. In the first type, litter worms can also be distinguished, which live in the litter layer and under no circumstances (even when the soil dries out or freezes) do not sink into the ground deeper than 5-10 centimeters. This type also includes soil-litter worms that penetrate the soil deeper than 10-20 centimeters, but only under unfavorable conditions, and burrowing worms that make constant deep passages (up to 1 meter or more), which they usually do not leave, but when feeding and mating, only the front end of the body protrudes to the surface of the soil. The second type can be divided into burrowing worms, living in the deep soil horizon, and burrowing worms, which have constant moves, but feed in the humus horizon.
Litter and burrowing worms inhabit places with waterlogged soils - the banks of water bodies, swampy soils, soils of humid subtropics. In the tundra and taiga, only litter and soil-litter forms live, and in the steppes, only soil forms proper. They feel best in conditions of coniferous-deciduous forests: all types of Lumbricidae live in these zones.
Lifestyle of worms
According to the way of life, worms are nocturnal animals, and at night one can observe how they swarm everywhere in large numbers, while remaining with their tails in minks. Stretching out, they rummage around the surrounding space, grab with their mouths (at the same time the throat of the worm turns slightly outward and then retracts back) damp fallen leaves and drag them into minks.
Earthworms are omnivores. They swallow a huge amount of earth, from which they assimilate organic substances, in the same way they eat a large number of all kinds of half-decayed leaves, except for very hard or having an unpleasant smell for them. When keeping worms in pots of earth, one can observe how they eat the fresh leaves of some plants.
Very interesting observations of earthworms were made by C. Darwin, who devoted a large study to these animals. In 1881, his book "The Formation of the Vegetative Layer by the Activity of Earthworms" was published. Charles Darwin kept earthworms in pots of earth and spent interesting experiences to study the nutrition and behavior of these animals. So, in order to find out what kind of food, besides leaves and earth, worms can eat, he pinned pieces of boiled and raw meat on the surface of the earth in a pot and watched the worms picking at the meat every night, and most of pieces were eaten. They also ate pieces of dead worms, for which Darwin even called them cannibals.
Half-rotted or fresh leaves are dragged by worms through the holes of minks to a depth of 6-10 centimeters and eaten there. Darwin observed how worms capture food items. If fresh leaves are pinned to the surface of the earth in a flower pot, then the worms will try to drag them into their burrows. Usually they tear off small pieces, grabbing the edge of the leaf between the prominent upper and lower lip. At this time, a thick, powerful pharynx protrudes forward and thereby creates a fulcrum for the upper lip. If the worm comes across a flat, large surface of a leaf, it acts differently. The anterior rings of the body are slightly drawn into the subsequent ones, due to which the anterior end of the body expands, becomes blunt with a small hole at the end. The pharynx moves forward, is pressed against the surface of the sheet, and then, without detaching, is pulled back and slightly expanded. As a result, a "vacuum" is formed in the hole at the front end of the body, applied to the leaf. The pharynx acts like a piston, and the worm sticks very firmly to the surface of the leaf. If you put a thin fading cabbage leaf on the worm, then on the back of the worm you can see a depression right above the head end of the animal. The worm never touches the veins of the leaf, but sucks out the delicate tissues of the leaves.
Worms use the leaves not only for food, but also plug the entrances to the minks with them. To this end, they also drag pieces of stems, withered flowers, scraps of paper, feathers, and tufts of wool into holes. Sometimes bundles of leaf petioles or feathers protrude from the worm's hole.
Leaves dragged into the burrows of worms are always crumpled or folded into a large number of folds. When the next leaf is pulled in, it is placed on the outside of the previous one, all the leaves are tightly folded and pressed against each other. Sometimes the worm enlarges the hole of its mink or makes another next to it in order to collect even more leaves. The worms fill the gaps between the leaves with moist earth thrown out of their intestines in such a way that the minks are completely clogged. Such clogged minks are especially common in the autumn before the wintering of the worms. The upper part of the passage is lined with leaves, which, according to Darwin, prevents the worm's body from contacting the cold and wet ground near the soil surface.
Darwin also described how earthworms dig holes. They do this either by pushing the earth in all directions, or by swallowing it. In the first case, the worm pushes the narrow front end of the body into the gaps between the particles of the earth, then inflates and contracts it, and thereby the soil particles move apart. The front end of the body works like a wedge. If the earth or sand is very dense, compacted, the worm cannot push the soil particles apart and acts in a different way. It swallows the earth, and, passing it through itself, gradually sinks into the ground, leaving behind a growing pile of excrement. The ability to absorb sand, chalk or other substrates completely devoid of organic matter is a necessary adaptation in the case when the worm, plunging into the soil from excessive dryness or cold, finds itself in front of unloosened dense layers of soil.
Minks of worms go either vertically or a little sideways. Almost always they are lined from the inside with a thin layer of black earth processed by animals. Lumps of earth ejected from the intestines are compacted along the walls of the mink by the vertical movements of the worm. The lining thus formed becomes very hard and smooth and adheres closely to the body of the worm, and the backward-curved bristles have excellent support points, which allows the worm to move forward and backward very quickly in the hole. The lining, on the one hand, strengthens the walls of the mink, on the other hand, protects the body of the worm from scratches. Minks leading down usually end with an extension, or a chamber. Here the worms spend the winter, singly or weaving into a ball of several individuals. The mink is usually lined with small stones or seeds, which creates a layer of air for the worms to breathe.
After the worm swallows a portion of the earth, whether it is done for food or for digging a passage, it rises to the surface to throw the earth out of itself. The discarded earth is saturated with intestinal secretions and, as a result, becomes viscous. After drying, lumps of excrement harden. The earth is thrown out by the worm not randomly, but alternately in different directions from the entrance to the hole. The tail works like a shovel. As a result, a kind of tower of excrement lumps is formed around the entrance to the burrow. Such turrets in worms different types have different shapes and heights.
Earthworm exit
When the worm protrudes from the mink to throw out excrement, it stretches its tail forward, but if it is to collect leaves, it puts out its head. Therefore, worms have the ability to roll over in their burrows. Worms do not always throw excrement on the surface of the soil. If they find some kind of cavity, for example, near the roots of trees, in newly dug up earth, they deposit their excrement there. It is easy to see that the space under stones or fallen tree trunks is always filled with small pellets of earthworm excrement. Sometimes animals fill the cavities of their old minks with them.
Life of earthworms
Earthworms in the history of the formation of the earth's crust played a much more important role than it might seem at first glance. They are numerous in almost all humid areas. Due to the digging activity of the worms, the surface layer of the soil is in constant motion. As a result of this "digging", soil particles are rubbed against each other, new layers of soil brought to the surface are exposed to carbon dioxide and humic acids, which contributes to the dissolution of many minerals. The formation of humic acids is due to the digestion of semi-decomposed leaves by earthworms. It has been established that worms contribute to an increase in the content of phosphorus and potassium in the soil. In addition, passing through intestinal tract worms, earth and plant residues are glued together with calcite, a derivative of calcium carbonate secreted by the calcareous glands of the digestive system of worms. The excrement compressed by contractions of the intestinal muscles is thrown out in the form of very strong particles, which are washed out much more slowly than simple lumps of earth of the same size and are elements of the granular structure of the soil. The amount and mass of excrement produced annually by earthworms is enormous. During the day, each worm passes through its intestines an amount of earth approximately equal to the weight of its body, i.e. 4-5 grams. Every year, earthworms throw a layer of excrement 0.5 centimeters thick onto the surface of the earth. C. Darwin counted them up to 4 tons of dry matter per hectare of pastures in England. Near Moscow, in a field of perennial grasses, earthworms annually form 53 tons of excrement per hectare of land.
Worms prepare the soil in the best way for the growth of plants: they loosen it so that there is no lump larger than they can swallow, and they facilitate the penetration of water and air into the soil. Dragging the leaves into their burrows, they crush them, partially digest them and mix them with earthen excrement. Evenly mixing the soil and plant residues, they prepare a fertile mixture, like a gardener. The roots of plants move freely in the soil along the paths of earthworms, finding rich nutritious humus in them. It is impossible not to be surprised when you think that the entire fertile layer has already passed through the bodies of earthworms and will pass through them again in a few years. It is doubtful, Darwin believes, that there are still other animals that would occupy such a prominent place in the history of the earth's crust as these essentially lowly organized creatures.
Thanks to the activity of worms, large objects, stones gradually sink deep into the earth, and small fragments of stones gradually grind in their intestines to sand. Darwin, describing how abandoned castles in old England were gradually sinking underground, emphasized that archaeologists should be indebted to earthworms for the preservation of a large number of ancient objects. After all, coins, gold jewelry, stone tools, etc., falling on the surface of the earth, are buried under the excrement of worms for several years and are thus reliably preserved until the earth covering them is removed in the future.
Earthworms, like many other animals, are affected by human activities. Their numbers are declining due to the excessive use of fertilizers and pesticides, cutting down trees and shrubs, and under the influence of overgrazing of livestock. 11 species of earthworms are included in the Red Book of the Russian Federation. Successful attempts have been repeatedly made to relocate and acclimatize worms of different species to those areas where they are not enough. Such activities are called zoological reclamation.
Earthworms are a family of large soil oligochaete worms Lumbricida, which phylogenetically belong to the class of oligochaete worms (Oligochete), subtype of girdle worms (Clitellata), type of annelids (Annelida) The type of annelids, or annelids, covers a significant number of species (about 9000) of higher worms .
The features of their structure are as follows (Fig. 1): The body of annelids consists of a head lobe, a segmented body and a posterior anal lobe. Most of the sense organs are located on the head lobe.
The musculocutaneous sac is well developed.
The animal has a secondary body cavity, or coelom, with each segment corresponding to a pair of coelomic sacs. The head and anal lobes do not have a coelom.
Rice. 1. Anterior end of the body of an earthworm:
A - right side;
B - ventral side;
1 - head blade;
2 - lateral bristles;
3 - female genital opening;
4 - male genital opening;
5 - vas deferens;
6 - belt;
7 - abdominal setae
The mouth opening is located on the ventral side of the first segment of the body. Digestive system, as a rule, consists of the oral cavity, pharynx, middle and posterior intestine, which opens with an anus at the end of the anal lobe.
Most rings have a well-developed closed circulatory system.
The function of excretion is performed by segmental organs - metanephridia. Usually there is one pair of metanephridia in each segment.
The nervous system consists of a paired brain, a pair of near-pharyngeal nerve trunks that go around the pharynx from the sides and connect the brain with the ventral nerve chain. The latter is a pair of more or less contiguous, and sometimes fused together, longitudinal nerve cords, on which paired ganglia are located in each segment - ganglia (with the exception of the most primitive forms).
The most primitive annelids are dioecious; in some annelids, hermaphroditism is expressed. The oligochaetes also have reduced fingers, parapodia, and gills. They live in fresh waters and in the soil.
The body of oligochaetes is strongly elongated, more or less cylindrical. The length of small oligochaetes barely reaches 0.5 mm, the largest representatives - up to 3 m. At the front end there is a small mobile head lobe (prostomium), devoid of eyes, antennae and palps. The body segments are outwardly identical, their number is usually large (from 30...40 to 600), in rare cases there are few segments (7...9). Each segment, except for the anterior one, which bears the oral opening, is provided with small setae protruding directly from the body wall. These are the remains of disappeared paralodia, usually arranged in four bundles (a pair of lateral and a pair of abdominal ones).
The number of setae in the fascicle varies. At the end of the body there is a small anal lobe (pygidium) with powder (Fig. 2).
Rice. 2. Appearance anal lobe (pygidium) of an earthworm:
a, b - Eisenia foetida (respectively, a hybrid and a common dung worm);
c - Lumbricus rubellus
The integumentary epithelium, which forms a thin elastic cuticle on the surface, is rich in mucous glandular cells. Mucous and proteinaceous unicellular glands are especially numerous in the region of the girdle, which is clearly visible during the breeding season of worms. Under the epithelium lie the developed layers of the skin-muscle sac - the outer annular and the more powerful inner longitudinal.
The digestive system consists of the pharynx, esophagus, sometimes goiter, muscular stomach, middle and hindgut (Fig. 3). On the side wall of the esophagus are three pairs of special calcareous glands. They are densely permeated with blood vessels and serve to remove carbopaths that accumulate in the blood.
Rice. 3. Earthworm Anatomy:
1 - prostomium;
2 - cerebral ganglia;
3 - pharynx;
4 - esophagus;
5 - side hearts;
6 - dorsal blood vessel;
7 - seed bags;
8 - testes;
9 - seed funnels;
10 - seed tube;
11 - dissipations;
12 - metanephridium;
13 - dorso-subneural vessels;
14 - middle intestine;
15 - muscular stomach;
16 - goiter;
17 - oviduct;
18 - egg funnels;
19 - ovary;
20 - seed receptacles.
Roman numerals indicate body segments
Excess lime comes from the glands into the esophagus and serves to neutralize the humic acids contained in the rotting leaves eaten by worms. Invagination of the dorsal wall of the intestine into the cavity of the middle intestine (tiflozol) increases the absorption surface of the intestine.
The circulatory system is arranged according to the same type as that of polychaete worms. In addition to the pulsation of the dorsal blood vessel, circulation is maintained by the contractions of certain annular vessels in the anterior part of the body, called the lateral or annular hearts. Since there are no gills and breathing takes place over the entire surface of the body, a dense network of capillary vessels usually develops in the skin.
The excretory organs are represented by numerous segmentally arranged metanephridia. Chlorogenic cells, also involved in excretion, cover the surface of the midgut and many blood vessels.
The decay products of chlorogenous cells often stick together and merge with each other into more or less large "brown bodies", which accumulate in the body cavity, and then are brought out through unpaired dorsal pores, which are present in many oligochaetes.
The nervous system is composed of a pair of supraesophageal ganglia, peripharyngeal connectives, and the ventral nerve cord (see Fig. 3). Only in the most primitive representatives of the ventral nerve trunks are widely spaced.
The sense organs in oligochaetes are extremely poorly developed.
The eyes are almost always absent. Interestingly, earthworms show light sensitivity, despite the fact that they do not have real visual organs - their role is played by individual light-sensitive cells scattered in large numbers in the skin.
The reproductive system of oligochaetes is hermaphrodite, the sex glands - gonads - are localized in a small number of genital segments (Fig. 4). In segments X and XI of the body of the worm, the seed capsules contain two pairs of testes, which are covered by three pairs of special seed sacs, the latter developing as protrusions of dissipations (see Fig. 1).
Rice. 4. Scheme of the structure of the reproductive system of the earthworm (according to Stephenson):
1- nervous system;
2 - testes;
3 - seminal receptacles;
4 - front and rear seed funnels;
5 - ovary;
6 - egg funnel;
7 - oviduct;
5 - seed tube;
IX... XIV - segments
Sex cells enter the seminal sacs from the seminal capsules after separation from the testes. In the seed sacs, the gums mature, and the mature spermatozoa return to the seed capsules. Special ducts serve for the withdrawal of livestock, namely: against each testis there is a ciliated funnel, from which the excretory channel departs. Both canals merge into a longitudinal vas deferens opening on the ventral side of segment XV.
The female reproductive system is formed by a pair of very small ovaries located in the XIII segment, and a pair of short funneled oviducts in the XIV segment. The posterior dissipation of the female segment forms egg sacs similar to seed sacs. In addition, this system includes two more pairs of deep skin invaginations on the ventral side of segments IX and X. They have no communication with the body cavity and serve as seed receptacles during cross-fertilization.
Finally, numerous unicellular glands, which form an annular thickening on the surface of the body - a belt, are indirectly related to the reproductive system. They secrete mucus, which serves to form a facial cocoon and a proteinaceous fluid, which feeds on the developing embryo.
Fertilization of earthworms is cross. Two animals are in close contact with the ventral sides, the heads are turned to each other. The belts of both worms secrete mucus, which envelops them in the form of two clutches, the belt of one worm is located against the openings of the seed receptacles of the other. From the male openings of both worms, sperm is released, which, with the contraction of the abdominal muscles, moves along the surface of the body to the girdle, where it enters the mucous membrane. At the same time, the partner's seminal receptors produce, as it were, swallowing movements and accept the seed entering the clutch. Thus, the seminal receptacles of both individuals are filled with someone else's seed. This is how copulation occurs, after which the worms disperse. Egg laying and fertilization occur much later. The worm secretes a mucous membrane around its body in the region of the girdle, in which eggs are laid. The sleeve slides off the worm through its head end. During the passage of the clutch past the IX and X segments, the seminal receptacles squeeze out into it the alien seed that is in them, with which the eggs are fertilized. The ends of the coupling then close, it is compacted and turns into an egg cocoon.
There is no larval stage in the development of oligochaetes. The eggs develop inside the egg cocoon, from which a fully formed worm emerges. In lower oligochaetes, several embryos develop in one cocoon containing an aqueous liquid. Eggs are rich in yolk, crushing occurs in a spiral type.
In higher oligochaetes, the cocoon contains a nutritious protein liquid, and the eggs are poor in yolk. The resulting embryo is called a "hidden" larva.
Representatives of the type Annelids (rings) are considered the most highly developed worms. This type includes the class Small-bristle worms. What features of the structure and life activity distinguish them from other worms?
Everyone has seen how, after a summer rain, earthworms appear on the surface of the earth (Fig. 18.1). They are driven out of the soil by water that fills all the passages of the worm. It quickly dissolves carbon dioxide, which is released as a result of decay of organic residues in the soil. Feeling a lack of oxygen and an excess of carbon dioxide, the worms crawl to the surface. But they don't stop here. As soon as there is less water in the soil, the worms return to their permanent habitat.
The earthworm spends the day underground, and at dusk it crawls out of the mink for a supply of food. Feeling the fallen leaf, the worm grabs it with its mouth and pulls it into the hole (Fig. 18.2). It feeds on leaves, organic debris and various microorganisms.
The length of the earthworm is 10-13 cm. Its body resembles a hose from washing machine: it consists of segments - dense rings connected by thin elastic ligaments. Thanks to them, the worm can freely fold and stretch. Several segments on the front of its body are thicker and noticeably paler than others. This is the so-called "yasok", which plays an important role in the reproduction of the worm.
The body of the animal is covered with a wet cuticle. If you run your finger over it from the front to the back end, you will feel that it is slippery and smooth, and when you do it in the opposite direction, it will seem rough to you. The fact is that on the body of the worm there are rows of bristles (Fig. 18.3), directed towards its rear end, like the hair of a smooth-haired cat. The slippery cuticle and bristles are adaptations of the worm to life in the soil. To advance in it, you need to have a smooth and slippery body. However, while moving against gravity, an animal with such a body will slide down. To avoid this, the worm and the necessary bristles.
Integument and movement of the earthworm. The earthworm, like all previously studied worms, has a skin-muscular sac covered with a cuticle. Rings have two muscle groups: circular and longitudinal. material from the site
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| Rice. 18.5. The scheme of movement of the earthworm |
How is the movement of an earthworm (Fig. 18.5) related to the work of its muscles? To make a move in the soil, the worm in the anterior segments of the body contracts the annular muscles, and in the segments located farther, the longitudinal ones. The front part of the body becomes thinner, increases in length and penetrates the soil. The next section of the body at this time shortens and thickens, resting against the walls of the passage.
Then the worm relaxes the annular muscles in the anterior region, and contracts the longitudinal ones. So it expands the hole in the soil. At the same time, in the segments of the next part of the body, the circular muscles contract, and the longitudinal muscles relax. Rhythmically contracting the annular and longitudinal muscles in the segments of different parts of the body, the worm makes a move. Sometimes, in order to make a move, the worm swallows lumps of earth that come across in its path.
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Many people underestimate the importance of the work of earthworms. These representatives of the invertebrate kingdom are best known for crawling out of the ground in large numbers after heavy rain. They are often used as bait by numerous fishing enthusiasts. Darwin also noted the fact that worms perform an important function in nature, acting as a kind of agricultural technicians. In the process of creating an extensive system of tunnels that the earthworm breaks through, excellent aeration is formed through the flow of air to the inner layers of the soil.
Thanks to excellent aeration, the respiratory activity of many plants is facilitated. Feeding on organic matter and waste, worms ensure the grinding of soil components, while enriching them with their secretions. Amazing Ability representatives of this species is the ability to disinfect huge areas of soil, sterilizing it from harmful bacteria. Thanks to countless burrows that form a semblance of a capillary system, perfect drainage and ventilation of the soil is ensured.
The body of an earthworm can reach three meters in length. However, on the territory of Russia, there are mainly individuals whose body length does not exceed 30 centimeters. In order to move, the worm uses small bristles that are located on different parts of the body. Depending on the variety, there can be from 100 to 300 segments. The circulatory system is closed and very well developed. It consists of one artery and one central vein.
The structure of the earthworm is very unusual. Breathing is realized with the help of special supersensitive cells. The skin produces a protective mucus with a sufficient amount of natural antiseptics. The structure of the brain is quite primitive and includes only two nerve nodes. According to the results of laboratory experiments, earthworms have confirmed their outstanding ability to regenerate. A severed tail grows back after a short period of time.
The genital organs of the earthworm are also arranged in a very unusual way. Each individual is a hermaphrodite. She also has male organs. According to biological factors, all such worms can be divided into several subgroups. Representatives of one of them are looking for food on the surface of the soil layer. Others use the soil itself as food and are extremely rarely shown from the ground.
Earthworm belongs to the ring type. Under the skin layer is a developed system of muscles, consisting of muscles of various shapes. The mouth opening, from which food enters the esophagus through the pharynx, is located on the front of the body. From there it is transported to the area of the enlarged goiter and the small size of the muscular stomach.
Burrowing and litter earthworms live in places with loose and moist soil. Preference is given to wet soils of the subtropics, swampy lands and the banks of various reservoirs. In the steppe territories, soil varieties of worms are usually found. Litter species live in the taiga and forest-tundra. The coniferous broad-leaved strip can boast of the highest concentration of individuals.
What kind of soil do worms like?
Why do earthworms love sandy and loamy soils? Such soil is characterized by low acidity, which is best suited for their life. The level of acidity above pH 5.5 is detrimental to the organisms of these representatives of the annular type. Moist soils are one of the prerequisites for population expansion. During dry and hot weather, worms go deep underground and lose the ability to reproduce.
The nature and lifestyle of the earthworm
The active and productive life of the earthworm falls on the dark time of the day. As soon as night falls, many individuals crawl out to the surface of the ground in search of food. However, the tail usually remains in the ground. By morning, they return to their burrows with prey, dragging pieces of food into them and masking the entrance to their shelter with blades of grass and foliage.
The role of earthworms in nature is difficult to overestimate. The worm literally passes through itself an incredible amount of soil mixture, enriching it with useful enzymes and killing harmful substances and bacteria. The worm moves by crawling. Pulling in one end of the body and clinging with bristles to the roughness of the earth, it pulls up the rear part, making its many passages in this way.
How do earthworms survive winter?
During the winter period, the vast majority of individuals hibernate. A sharp drop in temperature can instantly destroy the worms, so they try to burrow into the soil in advance to a depth often exceeding one meter. Earthworms in the soil perform the most important function of its natural renewal and enrichment with various substances and microelements.
Benefit
In the process of digesting semi-fermented leaves, the body of the worms produces specific enzymes that contribute to the active generation of humic acid. The soil that has been loosened by earthworms is optimal for a wide variety of representatives of the plant kingdom. Thanks to the system of intricate tunnels, excellent aeration and ventilation of the roots is provided. Thus, the movement of the earthworm is an important factor in the task of restoring the useful qualities of the soil.
The earthworm is in fact very useful for humans. It makes the soil layers fertile and enriches them with all sorts of nutrients. However, the total number of individuals in many regions of Russia is rapidly declining. This happens due to the uncontrolled introduction of pesticides, fertilizers and mineral mixtures into the soil. Numerous birds, moles, and various rodents also prey on earthworms.
What do earthworms eat?
At night, the earthworm crawls to the surface and pulls the half-decayed remains of plants and leaves into its shelter. Also, his diet includes soil rich in humus. One representative of the species can process up to half a gram of soil per day. Considering that up to several million individuals can be located simultaneously on an area of one hectare, they are able to act as indispensable soil converters.
After the rain, a large number of worms can be seen on the asphalt and soil surface, what makes them crawl out? Even the name "earthworms" indicates that they are very fond of moisture and become more active after rain. Consider a few possible causes why do earthworms crawl out after rain to the surface of the earth.
soil temperature
It is believed that the worms crawl to the surface in search of warmth, since after rain the soil temperature drops by several degrees, which causes discomfort for them.
Change in acid-base balance
Another theory says that the worms come to the surface due to a change in the acid-base balance of the soil after rain, it becomes more acidic, which negatively affects these diggers. According to the researchers, emergency evacuation to the soil surface saves them from death in an acidic environment.
Lack of air
The third theory explains that after rain, there is more oxygen in the upper layer of the soil, so the worms crawl out en masse. Water enriches the upper layers of the earth with oxygen, and many types of worms love moisture and vitally need enough oxygen. And through the surface of the body, oxygen is absorbed best in a humid environment.
Trips
British scientist Chris Low suggested that worms come to the surface of the earth during rain in order to make an extended journey to new territory. On the surface, worms can crawl much further than underground, and dry soil causes discomfort when moving, strong friction is created, grains of sand stick to the surface of the worm's body, injuring it. And after the rain, the surface of the earth is highly moistened, which allows them to freely travel to new areas of soil.
Sounds of the rain
Another scientist, Professor Joseph Gorris from the USA, suggested that earthworms are frightened by the sound of rain, since the vibrations that it creates are similar to the sound of the approach of their main enemy, the mole. That is why some fishermen use a technique to lure the bait to the surface: they insert a stick into the ground, fix a sheet of iron on its surface and pull it in such a way as to create vibration, while the short is transmitted to the ground through the stick. Frightened, the worms get to the surface of the earth and become easy prey for experienced fishermen.
Reproduction and lifespan of earthworms
The earthworm is a hermaphrodite. It has both female and male reproductive organs. However, he is not capable of self-fertilization. With the onset of warm temperatures required for reproduction climatic conditions individuals crawl in pairs, attaching to each other with the abdominal region, and produce a kind of seed exchange. After that, the clutch is transformed into a cocoon, in which the eggs develop.
Some varieties differ asexual reproduction. The body of the worm is divided in two, with one of the parts regenerating the anterior end, and the other regenerating the posterior end. There are also species of worms that reproduce without seed receptacles by laying spermatophores. The lifespan of worms can exceed ten years.
External structure
Body
The rain-howl, or earthworm (Fig. 51) has an elongated body 10-16 cm long. In cross section, the body is rounded, but, unlike roundworms, it is divided into 110-180 segments by annular constrictions. Each segment has 8 small elastic bristles. They are almost invisible, but if you run your fingers from the back end of the worm's body to the front, then we will immediately feel them. With these bristles, the worm rests when moving against the unevenness of the soil or against the walls of the passage.
Regeneration in earthworms is well expressed.
body wall
If we take the worm in our hands, we will find that the wall of its body is wet, covered with mucus. This mucus facilitates the movement of the worm in the soil. In addition, only through the moist wall of the body does the penetration into the body of the worm of oxygen necessary for breathing.
The body wall of the earthworm, like all annelids, consists of a thin cuticle, which is secreted by a single-layer epithelium. Under it is a thin layer of circular muscles, under the annular - more powerful longitudinal muscles. Contracting, the circular muscles lengthen the body of the worm, and the longitudinal muscles shorten it. Thanks to the alternating work of these muscles, the movement of the worm occurs.
Habitat
During the day, earthworms stay in the soil, making passages in it. If the soil is soft, then the worm penetrates into it with the front end of the body. In doing so, he first compresses the front end of the body, so that it becomes thin, and pushes it forward between the lumps of soil. Then the front end thickens, pushing the soil apart, and the worm pulls up the back of the body. In dense soil, the worm can eat its own way, passing the earth through the intestines. Lumps of soil can be seen on the surface of the soil - they are left here by worms. After a heavy rain that flooded their passages, the worms are forced to crawl out to the surface of the soil (hence the name - rain). In summer, the worms stay in the surface layers of the soil, and for the winter they dig minks up to 2 m deep.
Digestive system
The mouth is located at the anterior end of the body of the earthworm; the anus is in the back.
The earthworm feeds on decaying plant debris, which it swallows along with the earth. It can also drag fallen leaves from the surface. Food is swallowed as a result of contraction of the muscles of the pharynx. The food then enters the intestines. Undigested residues, together with the earth, are ejected through the anus at the posterior end of the body.
The intestine is surrounded by a network of blood capillaries, which ensures the absorption of nutrients into the blood.
Circulatory system
All secondary cavitary animals have a circulatory system, starting with annelids. Its occurrence is associated with a mobile lifestyle (compared to flat and primary cavity worms). The muscles of annelids work more actively and therefore require more nutrients and oxygen, which blood brings to them.
The earthworm (Fig. 52) has two main blood vessels: the dorsal, through which blood moves from the rear end of the body to the front, and the abdominal, through which blood flows in the opposite direction. Both vessels in each segment are connected by annular vessels.
Several thick annular vessels are muscular, due to their contraction, the movement of blood occurs. Muscular vessels ("hearts"), located in 7-11 segments, push blood into the abdominal vessel. Valves in the "hearts" and spinal vessels prevent backflow of blood. Thinner ones depart from the main vessels, branching then into the smallest capillaries. In these capillaries, oxygen enters through the surface of the body, and nutrients from the intestines. From the capillaries branching in the muscles, carbon dioxide and decay products are released. Blood moves all the time through the vessels and does not mix with the cavity fluid. Such a circulatory system is called a closed one. Blood contains hemoglobin, which is able to carry more oxygen; she is reddish.
A closed circulatory system allows you to significantly increase the metabolic rate. In annelids, it is twice as high as in flatworms that do not have a blood pumping system.
Respiratory system
The respiratory system of the earthworm is absent. Absorption of oxygen is carried out through the surface of the body.
excretory system
The excretory system of an earthworm consists of paired tubes in each segment of the body (with the exception of the terminal ones) (Fig. 53).
At the end of each tube there is a funnel that opens as a whole, through which end products of vital activity (represented mainly by ammonia) are brought out.
Nervous system
The nervous system of the earthworm (Fig. 52) is of a nodular type, consisting of a peripharyngeal nerve ring and an abdominal nerve chain.
In the abdominal nerve chain there are giant nerve fibers that, in response to signals, cause contraction of the muscles of the worm. Such a nervous system ensures the coordinated work of the muscle layers associated with the burrowing, motor, food and sexual activity of the earthworm.
Behavior
Reproduction and development
Earthworms are hermaphrodites. In the process of copulation of two individuals, mutual fertilization occurs, that is, the exchange of male gametes, after which the partners diverge.
The ovaries and testicles are located in different segments at the anterior end of the body. The location of the reproductive organ system is shown in Figure 51. After copulation, a belt is formed around each worm - a dense tube that secretes the cocoon shell. Nutrients enter the cocoon, which the embryos will subsequently feed on. As a result of the expansion of the rings located behind the cocoon, it is pushed forward to the head end. At this time, 10-12 eggs are laid through the opening of the oviduct into the cocoon. Further, when the cocoon moves, spermatozoa from the seed receptacles received from another individual during copulation enter it, and fertilization occurs. After that, the cocoon slides off the worm and its holes quickly close. This prevents the eggs it contains from drying out.
The development of earthworms is direct, that is, they do not have larvae, a young worm hatches from the egg.
Value (role) in nature
Making passages in the soil, earthworms loosen it and contribute to the penetration of water and air into the soil, which are necessary for the development of plants. The mucus secreted by the worms sticks together the smallest particles of the soil, thereby preventing its spraying and erosion. Dragging plant residues into the soil, they contribute to their decomposition and the formation of fertile soil.
Position in systematics (classification)
Earthworms are classified as annelids, class Belt worms, subclass Small-bristle worms (Oligochetes).
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